Camera Sensor Sizes Explained

Sensor size is the physical size of the light-sensitive chip in a camera, from medium format (about 44 x 33 mm) through full frame (36 x 24 mm), APS-C (about 23.5 x 15.6 mm), Micro Four Thirds (17.3 x 13 mm) and 1-inch type (13.2 x 8.8 mm) down to phone sensors a few millimetres across. It matters because it decides how much of a lens’s image you record, how easily you can blur a background, how much light each picture is built from, and how big and heavy the lenses have to be.

The night sky above shows the stakes. Fifteen seconds is about as long as a 14mm lens can stay open before the stars start to streak, and f/1.8 is as wide as the lens goes. With shutter and aperture both used up, the amount of light a single exposure like this is made from, and so how clean it looks, comes down to how many square millimetres of sensor sit behind the lens.

One idea explains almost everything on this page: a smaller sensor records a crop from the middle of the picture a larger one would record, and that crop is then enlarged more to reach the same viewing size. The exposure on each square millimetre is the same on every format. What changes is the size of the crop, and everything else (field of view, depth of field, noise, reach, lens size) follows from that. Full frame versus crop sensor sets the two most common formats, full frame and APS-C, side by side. This page covers the whole range.

The common sensor formats, with dimensions and crop factors

Full frame is the reference because it matches the 36 x 24 mm frame of 35mm film, the format most lenses and focal lengths were described in for decades. The crop factor of any other format is the full frame diagonal (43.3 mm) divided by that format’s diagonal.

Exact dimensions differ by a fraction of a millimetre between manufacturers, which is why the APS-C figures say “about”. Some studio cameras use a larger medium format sensor of about 54 x 40 mm, with a crop factor near 0.65x. The secondary cameras on a phone (ultra-wide and telephoto) are usually smaller than its main sensor. The last column is total light across the whole sensor at the same f-number and shutter speed, explained below.

Diagonals are used because the formats do not all share one shape. Full frame, APS-C and 1-inch sensors are 3:2, while Micro Four Thirds, most phone sensors and 44 x 33 mm medium format are 4:3, squarer. That makes a crop factor a slightly rough guide when the shapes differ. Micro Four Thirds is 2.08 times narrower than full frame but only 1.85 times shorter, so a 25mm lens on it frames a little tighter than a 50mm on full frame from side to side and a little looser from top to bottom. Aspect ratio covers what the shape of the frame does to a composition.

Want the full frame equivalent of every lens you own without doing the sums? The crop factor calculator gives equivalent focal lengths and apertures for each format.

Why a “1-inch” sensor is not an inch across

A 1-inch type sensor measures 13.2 x 8.8 mm, with a diagonal of 15.9 mm, against 25.4 mm in an inch. The name is inherited from video camera tubes, which were used before solid-state sensors existed. A tube was sold by the outside diameter of its glass envelope, and the usable picture area inside was much smaller, with a diagonal of roughly two thirds of that diameter. When chips replaced tubes, the industry kept the old sizes as labels so that lenses could be matched to them. A “1-inch type” sensor is one with about the imaging area of a one-inch tube.

The same convention explains the fractions used for small sensors. A 1/2.3-type sensor is not 1/2.3 of an inch (11 mm) across; its diagonal is about 7.7 mm. As a working rule, multiply the nominal figure by about two thirds to estimate the real diagonal, and remember that with fractions a bigger number under the line means a smaller sensor: 1/1.3-type is considerably larger than 1/2.5-type.

Other names have their own histories. “Four Thirds” refers to the 4/3-inch type designation of that sensor, again far larger than its real 21.6 mm diagonal. “APS-C” comes from the “classic” frame of the Advanced Photo System film format, which was close to the same size. For video, the APS-C frame is close in size to the Super 35 film format used in cinema, so it gives a field of view and depth of field near that standard. Since the inch-type names mislead, compare sensors in millimetres or by crop factor.

Field of view: the same lens on different sensors

A lens projects a circular image, and the sensor records a rectangle from the middle of it. A smaller sensor records a smaller rectangle, so the picture shows a narrower view. The lens has not changed and neither has its focal length: a 50mm lens is a 50mm lens on any camera. Only the amount of its image that is used has changed.

Any sensor smaller than full frame is called a crop sensor for exactly this reason: it records only the central portion of the image a lens projects, as if the middle of a full frame picture had been cropped out. On full frame, a 50mm lens is called a normal lens because its focal length is close to the sensor’s 43 mm diagonal, so the view looks natural. On each format, the normal lens is the one whose focal length is near that format’s diagonal: about 28mm on APS-C and about 22mm on Micro Four Thirds.

To describe the view in familiar terms, multiply the focal length by the crop factor. A 50mm lens gives the view of a 75mm lens on 1.5x APS-C, 80mm on 1.6x APS-C and 100mm on Micro Four Thirds. On 44 x 33 mm medium format it gives the view of about 40mm. In the other direction, to get the view of a 24mm lens on full frame you need 16mm on APS-C, 12mm on Micro Four Thirds and about 9mm on a 1-inch sensor.

Perspective, the way near and far things relate in size, depends only on where the camera stands, so from the same spot the smaller sensor’s frame matches a crop from the larger one exactly.

If the crop factor does not change perspective, why do long lenses seem to flatten a scene? Lens compression runs the crop test and shows that distance does it, not the lens.

The narrower view is welcome for distant subjects: a 300mm lens gives the view of a 450mm lens on 1.5x APS-C, which is why wildlife and sport photographers often use smaller formats with a telephoto lens. The cost falls on wide-angle work, where a 16mm lens frames like a 24mm, so smaller-format systems offer dedicated ultra-wide lenses to compensate.

Try it: put the same lens on each sensor and see how much of the scene each one records, and what lens and aperture would give the same picture on full frame.

Does the narrower view mean you need a faster shutter speed to avoid shake? The hand-holding rule has a chart for full frame and crop sensors.

Depth of field at the same framing

Sensor size does not change depth of field through some property of the chip. It changes the lens you need. To frame a subject the same way from the same position, a larger sensor needs a longer focal length. At the same f-number, a longer lens has a physically wider opening, and a wider opening gives a shallower zone of sharpness and more background blur.

The size of the difference follows the crop factor. For the same framing and distance, f/2.8 on full frame gives about the depth of field of f/1.8 on APS-C, f/1.4 on Micro Four Thirds and f/1.0 on a 1-inch sensor. Read the other way, f/2.8 on Micro Four Thirds looks like f/5.6 on full frame.

“Small sensors have more depth of field” is only true at the same framing, and it is worth knowing why. Keep the same lens, the same spot and the same f-number, and swap a full frame body for an APS-C one. The smaller sensor records a crop of the very same image, with exactly the same blur in it. Viewed at the same size, that crop is enlarged 1.5 times more, so its blur looks a little larger, not smaller. The deep focus of small formats comes entirely from the shorter lens they use to get the same picture.

This cuts both ways. A large sensor makes soft backgrounds easy and deep focus harder. A small sensor does the reverse: a phone keeps a whole scene sharp without effort, and cannot blur a background optically unless the subject is very close, which is why phones simulate the effect in software. For close-up work and landscapes, deep focus at a moderate f-number is an advantage.

The phone above used a 4mm lens at f/2.6, an opening about 1.5 mm across. A full frame camera framing the same scene would use roughly a 28mm lens, whose opening at f/2.6 is about 11 mm. That difference in opening is why the phone kept everything sharp. The depth of field calculator works out the zone of sharpness for any lens, distance and f-number.

Try it: set a view and an f-number, then switch between full frame, APS-C and a phone sensor. The framing stays the same, and you can watch how much of the row of figures stays sharp on each.

Total light, noise and dynamic range

An exposure setting such as f/4 at 1/100 second puts the same amount of light on every square millimetre of any sensor. That is why the same settings give the same brightness on every format, and why a light meter does not care what camera it is used with. But a larger sensor has more square millimetres, so it collects more light in total, in proportion to its area.

Total light is what governs noise in the finished picture. Light arrives as individual photons, with a natural randomness that shows as grain, and the more of them a picture is built from, the smoother it looks. When pictures from two formats are viewed at the same size, the one made from more light is cleaner. The last column of the format table turns the area ratios into stops:

• Full frame gathers about 1.2 stops more than APS-C, about 2 stops more than Micro Four Thirds and about 3 stops more than a 1-inch sensor.
• In ISO terms, the noise of a full frame camera at ISO 1600 is roughly matched by APS-C at about ISO 700, Micro Four Thirds at ISO 400 and a 1-inch sensor at about ISO 220.

Dynamic range follows the same logic. A larger sensor can hold more light in total before its highlights clip, so its shadows are built from more light and stay cleaner when you lift them. For sensors of similar design the gap stays roughly the same across the ISO range, close to the area difference in stops. Dynamic range explained goes further into how ISO and sensor design shape it.

Two cautions keep these numbers honest. First, they assume sensors of similar design. Differences between sensor generations and designs can be worth up to a stop or so in either direction, so a well designed small sensor can match an older or simpler large one. Second, the advantage only exists when the larger sensor is allowed to gather more light, which the next section explains.

Equivalence in one rule

Equivalence is the method for finding settings on two formats that produce the same picture: same framing, same depth of field, same motion blur and about the same noise, viewed at the same size. The rule is short.

Multiply both the focal length and the f-number by the crop factor to get the full frame equivalent. Keep the shutter speed the same. For matching noise, multiply the ISO by the crop factor squared.

So a 25mm f/1.4 lens on Micro Four Thirds (2x) behaves like a 50mm f/2.8 lens on full frame. A 35mm f/1.8 lens on 1.5x APS-C behaves like about 53mm f/2.7. The table shows one full frame picture and its equivalents.

Every row has the same angle of view and the same lens opening, about 18 mm across (50 divided by 2.8, or 25 divided by 1.4). The same opening, pointed at the same scene for the same time, collects the same total light. That is the real lesson of equivalence: the width of the lens opening does the work, and the sensor behind it decides which lenses are practical. An f/1.0 lens for a 1-inch sensor is rarely made, so in practice the larger formats can reach looks and light levels the smaller ones cannot.

Three things equivalence does not say:

• The f-number for exposure does not change. f/1.4 is f/1.4 on every format when you are setting shutter speed and ISO. The multiplied figure describes depth of field and total light only.
• The lens does not change. Its focal length and its maximum aperture are fixed properties, whatever body it is mounted on.
• A bigger sensor is not automatically cleaner. If you need the same depth of field on both formats, you stop the larger one down and raise its ISO, and the noise advantage disappears.

The simple rule also assumes the subject is well beyond close-up range. At macro distances a lens’s working f-number rises as it focuses closer, by different amounts for the longer and shorter lens, so the multiplied figures become a rough guide there.

Finding a phone’s crop factor from its own numbers

Phones rarely list their sensor dimensions, but most record two focal lengths in each photo’s details: the real one, a few millimetres, and a “35mm equivalent”. Divide the second by the first and you have the crop factor. A main camera listed as 4.2mm with a 26mm equivalent has a crop factor of about 6.2. Its f/1.8 lens is then about f/11 on full frame for depth of field and total light (1.8 times 6.2), which is why its backgrounds stay recognisable and why it leans on merging many frames in dim light. It still exposes as f/1.8.

Pixel size versus sensor size

Pixel size is set by two things: how big the sensor is and how many pixels are on it. Divide the sensor’s width by the number of pixels across it to get the pixel pitch: the distance from the center of one pixel to the center of the next, measured in micrometres (thousandths of a millimetre). Pixel pitch and pixel size are usually used to mean the same thing, though the light-sensitive part of each pixel is a little smaller than the pitch. Pitch is not resolution: resolution is the number of pixels, and pitch is how tightly they are packed, so the same pixel count gives a larger pitch on a larger sensor.

It is tempting to read this as a ranking of quality. For a single pixel it is: a larger pixel catches more light and is less noisy. But pictures are not viewed one pixel at a time. When two images are shown at the same size, the noise you see depends mostly on the total light gathered by the sensor, not on how finely it was divided. A 45-megapixel full frame sensor has smaller pixels than a 24-megapixel one, yet at the same print size the two are close in noise, and the 45-megapixel file holds more detail. Very small pixels do lose a little in the deepest shadows and at very high ISO, where electronic noise added per pixel starts to count.

So judge noise by sensor size first, and treat pixel count as a question of detail and cropping room. How image sensors work goes into what happens inside each pixel, and the megapixel table turns pixel counts into print sizes.

Pixel density also settles the question of “reach”. A smaller sensor behind the same lens does not magnify anything; it records the middle of the picture, exactly as if you had cropped it later. Whether that crop holds more detail depends on how tightly its pixels are packed. A 24-megapixel APS-C sensor packs its pixels as tightly as a full frame sensor of about 56 megapixels would. With the same lens, it puts more pixels on a distant bird than a 24-megapixel full frame camera, whose central APS-C area holds only about 10 megapixels. Against a 45-megapixel full frame body, whose central APS-C area holds about 19 megapixels, the lead shrinks to a small margin. The advantage comes from pixel density, not from the sensor being small, and it only holds if the lens is sharp enough to feed those pixels.

Lens size, image circles and diffraction

A lens must project an image circle big enough to cover the sensor, and for a given angle of view its focal length grows with the format. Both make lenses for larger sensors longer, wider and heavier. A 300mm f/4 lens for full frame and a 150mm f/4 lens for Micro Four Thirds give the same view and the same exposure, but the first has a 75 mm opening and the second a 37.5 mm one, and the glass is sized to match.

Equivalence explains the catch. The 150mm f/4 lens is the equal of a 300mm f/8 on full frame for depth of field and total light. The smaller system is lighter because it gathers less light, not because of a trick. When that trade suits your subjects, it is a real benefit.

Image circles also decide which lenses work on which bodies. A lens made for full frame covers an APS-C sensor easily, with room to spare. A lens made for APS-C, mounted on a full frame body, leaves the corners dark or black, because its circle is too small; many cameras respond by switching to a crop mode that uses only the APS-C area. A related belief is that a full frame lens performs better on APS-C because only its sharp centre is used. The centre is usually the sharpest part, but the smaller frame is enlarged 1.5 times more to reach the same print, which magnifies every flaw of the lens by the same amount. There is no free gain in either direction.

Can a lens made for a smaller sensor go on a full frame body of the same make? Lens mount covers mounts shared by different sensor sizes and what happens when you adapt between them.

Diffraction, the softening that appears at small apertures, scales the same way. Its effect on the finished picture is about equal at f/16 on full frame, f/11 on APS-C, f/8 on Micro Four Thirds and f/5.6 on a 1-inch sensor. Smaller formats therefore have a narrower range of useful f-numbers, though their depth of field is already deep, so they need small apertures less often.

When sensor size changes your pictures, and when it does not

Often less than the discussion around it suggests, and occasionally a great deal. The differences between neighbouring formats are one to two stops. That is real, but it is also the size of the difference between an f/2.8 zoom and an f/1.8 prime, or between a steady hand and a tripod. An APS-C camera with an f/1.8 lens gathers about as much total light as a full frame camera with an f/2.8 lens.

Sensor size matters most when:

• You photograph moving subjects in dim light (indoor events, sport under floodlights, street scenes at night) and cannot lengthen the exposure.
• You want very shallow depth of field from normal working distances, as in many portraits.
• You photograph the night sky, where exposures are limited by the movement of the stars and every bit of light counts, as in the picture at the top of this page. Astrophotography covers the settings.
• You make large prints from files with heavy shadow recovery.

It matters least when:

• There is plenty of light, or the camera is on a tripod and the subject is still. At base ISO every format from 1-inch upward produces a clean file.
• You need deep focus, as in close-up work or landscapes with a near foreground. The larger sensor has to stop down further, which hands back its light advantage.
• The pictures are seen on phone and laptop screens, where a one-stop difference in noise is invisible.
• Weight decides whether the camera comes along at all.

Phones show how far the principle can be stretched. A phone sensor gathers a small fraction of the light of a large one in a single exposure, so phones take many frames and merge them, which is a way of collecting more total light over time. It works well for still scenes and less well for anything that moves. The comparison is taken further in smartphone versus camera.

How does a phone turn a burst of dark, noisy frames into one clean night picture? Computational photography explains night mode, multi-frame capture and synthetic background blur.

Common mistakes with sensor size

• Taking “1-inch” literally. The name suggests a sensor 25 mm across when its diagonal is under 16 mm, and with fractional sizes 1/1.7-type is larger than 1/2.5-type, not smaller. Fix: compare dimensions in millimetres or crop factors.
• Converting the focal length but not the f-number. Calling a 25mm f/1.4 lens on Micro Four Thirds “a 50mm f/1.4” overstates its background blur by two stops. Fix: multiply both by the crop factor when comparing looks.
• Converting the f-number for exposure. The opposite slip: thinking f/1.4 on a small sensor exposes like f/2.8. Fix: set exposure with the f-number printed on the lens, on any format.
• Thinking the crop factor changes the lens. The focal length and perspective stay the same; only the recorded area changes. Fix: think of a smaller sensor as a crop from the middle of the larger one’s picture.
• Believing small sensors always give deeper focus. With the same lens and position they record the same blur, enlarged more. Fix: remember the deeper focus comes from the shorter lens used for the same framing.
• Blaming megapixels for noise. High-resolution files look noisier pixel by pixel and about the same at the same print size. Fix: compare at the same output size.
• Expecting a larger sensor to fix deep-focus work. Stopped down to match depth of field, the formats perform alike. Fix: choose the format for the light and depth of field you actually use.

Try this: measure your phone against your camera in ten minutes

1. Take a picture with your phone’s main camera and open its details. Divide the 35mm equivalent focal length by the real one to get the crop factor, and multiply the phone’s f-number by it to get its equivalent f-number. Then divide the real focal length by the f-number to get the width of the lens opening in millimetres. Write both down.
2. If you have a camera, do the same for its lens wide open: the f-number times the crop factor from the table above, and the focal length divided by the f-number.
3. Put a mug on a table with a busy background, such as a bookshelf or a string of lights, at least three metres behind it. Photograph the mug with the camera wide open, then with the phone in normal photo mode (not portrait mode), moving so the mug is the same size in both frames.

Judge it this way: the picture taken through the wider opening should show the more blurred background, and with a distant background the out-of-focus highlights grow in proportion to the opening. A 33mm lens at f/1.8 on APS-C has an opening of about 18 mm; a phone lens of 4.2mm at f/1.8 has one of about 2.3 mm, so the camera’s highlights should be roughly eight times wider. When the two cameras share the same equivalent focal length, the same ratio falls out of their equivalent f-numbers. If you have no camera, repeat step 3 with the phone’s main and telephoto cameras: the one with the larger real opening gives the softer background.

Frequently asked questions about sensor size

Is a bigger sensor always better?

No. A bigger sensor can gather more light and blur backgrounds more, at the price of larger, heavier lenses and shallower focus. When you need deep depth of field or have plenty of light, a smaller sensor gives an equally good picture from a lighter kit.

What is the crop factor of each sensor size?

Full frame is 1.0x. APS-C is 1.5x or 1.6x, Micro Four Thirds is 2.0x, 1-inch type is 2.7x and 44 x 33 mm medium format is about 0.79x. Phone main cameras are roughly 3.5x to 6x.

Does a crop sensor make my lens longer?

No. The focal length is unchanged; the sensor records a smaller part of the lens’s image, so the view is narrower. Multiply by the crop factor to find the full frame lens that would give the same view.

Do I need different exposure settings on a smaller sensor?

No. A given f-number, shutter speed and ISO give the same brightness on every format, so a hand-held light meter or an exposure chart works on any camera. Sensor size changes how clean that exposure looks, not how bright it is.

Does sensor size affect megapixels?

Not directly. Any pixel count can be put on any size of sensor. For the same count, a larger sensor has larger pixels, and at the same output size it produces less noise because it gathered more light overall.

Why do phone photos have everything in focus?

Phone sensors are tiny, so their lenses are only a few millimetres long with openings a few millimetres wide at most. That gives a depth of field similar to a full frame lens at around f/6 to f/11, which keeps near and far sharp together.