Camera Sensor Sizes Explained

Sensor size is the physical size of the light-sensitive chip in a camera. The common formats run 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. Size sets the field of view a lens gives, how easily backgrounds blur, how much light is gathered, and how big the lenses must be.

This guide lists the formats with their dimensions and crop factors, explains what a change of size does and does not alter, and gives one rule for comparing lenses across formats. The individual formats have their own short entries at full frame, APS-C and crop sensor, and full frame versus crop sensor compares those two directly. This page covers the whole range and the reasoning behind it.

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. 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.

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.

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. An inch is 25.4 mm.

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. 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.

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.

The picture is otherwise the same as the centre of the larger format’s picture. Perspective depends on where the camera stands, so from the same spot the smaller sensor’s frame matches a crop from the larger one. Whether a smaller format gives more “reach” depends on pixels, which is covered further down.

Depth of field at the same framing

Sensor size does not change depth of field by 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.

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.

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. 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. At base ISO, a larger sensor can hold more light before its highlights clip, which leaves cleaner shadows to lift in editing. The gap narrows as ISO rises.

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. 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.

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.

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.

Pixel density also settles the question of “reach”. 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. The advantage comes from the pixel density, not from the sensor being small, and it only holds if the lens is sharp enough to feed those pixels.

Lens size, weight 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.

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.

Does sensor size matter for your photography?

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.
• 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.

Common mistakes

• Taking “1-inch” literally. The name suggests a sensor 25 mm across when its diagonal is under 16 mm. 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, and neither when setting exposure.
• 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.
• Judging noise at 100 percent. High-resolution files look noisier pixel by pixel and no noisier 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

Take fifteen minutes with your own camera and a phone. First, find your camera’s sensor dimensions in its manual, work out the diagonal, and divide 43.3 by it to get the crop factor. Multiply the focal length and maximum f-number of each lens you own by that figure and write the full frame equivalents down. Second, place a small object on a table about a metre from a busy background. Photograph it with the camera at its widest aperture and again with the phone’s main camera, moving so that the object is the same size in both frames. Compare the backgrounds. Then compare your written equivalents with what you see: the phone’s lens, at a full frame equivalent of roughly f/6 to f/11, keeps the background recognisable, while the camera’s does not.

Frequently asked questions

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.

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 stopped well down, which keeps near and far sharp together.

Related guides

• Full frame versus crop sensor: the two most common formats compared in detail.
• Crop factor: the multiplier and how to use it.
• Crop factor calculator: equivalent focal lengths and apertures without the arithmetic.
• How image sensors work: from photons to pixels, and the designs that change sensor performance.
• Depth of field: what controls the zone of sharpness.
• Medium format: the formats larger than full frame.
• Dynamic range explained: how sensors handle bright and dark in one frame.