Metering in Photography: How Your Camera Measures Light

Metering is how your camera measures light to decide how bright the picture should be. Every time you half-press the shutter, the meter reads the scene and suggests an exposure: a mix of aperture, shutter speed and ISO. It matters because the meter makes the same assumption every time, and that assumption is wrong for snow, white dresses, black dogs, stages and night streets. Once you know what it assumes, you can predict when it will miss and by how much.

The whole subject rests on one idea: a meter makes whatever it reads come out middle gray. It does not know what your subject is or what color it should be. The modes, the compensation dial, the gray card and the histogram are all ways of working with that one fact.

What a camera meter actually measures

The meter in your camera is a reflected light meter, which is why camera metering is also called reflective metering. It reads the light coming back from the scene through the lens, adds it up across the part of the frame it is told to look at, and works out the settings that would turn that amount of light into a medium tone in the file. That medium tone is middle gray, the tone halfway between black and white as your eye judges it.

Think of the meter as a light counter with no eyes. Point it at a sheet of white paper, a sheet of black paper and a gray card, each filling the frame, and it will recommend three exposures that make all three look roughly the same gray. The white paper gets less exposure, the black paper gets more, and the meter reports success every time. It cannot tell a white thing in dim light from a gray thing in bright light, because both send the same amount of light to the lens.

Most scenes are a mix of light and dark parts that average out to something close to middle gray, which is why the meter is right so often. The trouble starts when the frame is mostly bright or mostly dark for a real reason. Then the meter “corrects” something that was never wrong.

Is middle gray 18 percent?

You will often read that meters are set for 18 percent gray, the reflectance of a standard gray card. In practice most camera meters are calibrated a little lower, closer to 12 or 13 percent. The gap between 18 and 12.5 percent works out to about half a stop (18 divided by 12.5 is 1.44, and a stop is a factor of 2, so it is log base 2 of 1.44, or 0.53 stops). That is small enough to ignore most of the time, and it explains why a careful reading off a gray card sometimes looks a touch dark.

Why snow turns gray and black dogs turn gray

Fill the frame with sunlit snow and the meter sees a lot of light. It assumes the scene is an average scene in very bright light, so it cuts the exposure until the snow lands at middle gray. The result is dull gray snow, usually one to two stops too dark. The same happens with white sand, a white wall, fog, a bride’s dress filling the frame, or a page of text.

Point the same meter at a black dog, a dark suit or a coal pile and it does the opposite. It sees little light, assumes an average scene in dim light, and adds exposure until the black becomes gray. Black fur turns charcoal, shadows go muddy, and any bright edges around the subject clip to pure white.

The fix is the same in both cases: tell the camera the truth with exposure compensation. A bright subject needs plus compensation, so the white goes back to white. A dark subject needs minus compensation, so the black stays black. The direction feels backwards at first, because you are adding light to a scene that already looks bright. You are not brightening the scene; you are undoing the meter’s correction.

Try it in the simulator: in Aperture, Shutter or Auto mode with Evaluative metering, use exposure compensation until the snow comes out white instead of gray.

Not sure which way to turn the dial or by how much? Exposure compensation works through it scene by scene.

Reading the meter scale in your viewfinder

Most cameras show the meter as a scale running from about minus 3 to plus 3 with a mark at zero, usually in third-stop ticks. Zero means one thing only: “at these settings, the part of the frame I am reading will come out middle gray.” Each tick to the left or right is a third of a stop darker or brighter than that.

A centered needle is a statement about tone, not about quality. If the meter is reading snow and the needle sits at zero, the snow will be gray. If you want the snow white, you want the needle at about plus 2 while the meter reads the snow. Once you see the scale as “how far from middle gray,” every reading becomes useful, including the ones that look wrong.

How the scale behaves depends on your shooting mode:

• In aperture priority, shutter priority or program, the camera keeps the needle at whatever compensation you set, adjusting the setting it controls. Plus 1 compensation means “make the metered area one stop brighter than middle gray.”
• In manual, the needle simply reports where your chosen settings fall. You move it by changing aperture, shutter speed or ISO. On most cameras the compensation dial does nothing in full manual; on some it shifts the zero point of the scale, so the needle shows your settings against the meter’s reading plus your compensation.
• In manual with auto ISO, the camera picks the ISO to hit the meter’s target, so compensation starts working again on most bodies.

One thing the mode never does is change what a given exposure looks like. A frame shot at f/8, 1/125 and ISO 100 is identical whether the camera was set to spot, matrix or center-weighted. The metering mode only changes the advice. That is why switching metering modes in manual seems to do nothing until you act on the new reading.

Meter a tone, not the scene

The most reliable way to use any meter is to aim it at something whose tone you know, then place that tone where it belongs. If you meter something that really is mid-toned and set the needle to zero, everything else in the same light falls into place on its own: whites go white, blacks go black. If you meter something lighter or darker, you shift the needle by a known amount.

These offsets are approximate starting points, not laws. Surfaces vary, and so does how much headroom your camera has above middle gray before highlights clip (somewhere around 2.5 to 3.5 stops, depending on the camera and its settings). Use them, then check the result on the histogram.

Tone you metered	Where it should sit	Set the needle or compensation to
Sunlit snow with texture	About 2 stops above middle gray	+2 (up to +2 1/3)
White shirt or paper, with detail	About 2 stops above	+2
Light skin in even light	About 1 stop above	+2/3 to +1
Weathered wood, gray stone, green grass in sun, blue sky away from the sun	Close to middle gray	0
Dark foliage, dark denim	About 1 stop below	-1
Black fur or a black coat, with detail	About 2 stops below	-2
Black with no detail needed	3 stops or more below	-3 or less

Skin deserves a note of its own. Skin comes in every tone from very light to very dark, and a spot reading turns any of them into middle gray. Lighter skin usually needs plus 2/3 to plus 1; deeper skin may need no change or minus compensation. Meter the face, then adjust for the face you are actually looking at. Photographing skin tones goes further into getting both exposure and color right.

Where would the spot land? A worked example

Look at the swan and ducks at the top of this page. It was shot at f/8, 1/640 and ISO 100, and the swan and snow keep their white with feather and crust detail. Here is what a spot meter, followed blindly with the needle at zero, would have done from different points in that frame. Each figure assumes the same f/8 and ISO 100 and moves only the shutter speed, in third-stop steps.

• Spot on the sunlit snow or the swan’s back (about 2 stops above middle gray): the meter asks for 2 stops less light, 1/2500 instead of 1/640. The swan and the snow come out middle gray, the ducks go murky.
• Spot on a hen mallard’s brown back (close to middle gray in sun): the reading lands near the exposure that was used, around 1/640. This is “meter a tone” working as intended.
• Spot on the shaded underside of a drake (about 2 stops below): the meter asks for 2 stops more light, 1/160. The ducks look fine, but the swan now sits about 4 stops above middle gray and blows to flat white with no feathers.

Same scene, same light, a 16 times difference in shutter speed (1/2500 to 1/160 is four stops), all from where one small circle happened to land. That is why spot metering gives you control, not correctness. It does exactly what you point it at, and the thinking is yours. The Zone System is this same idea worked out in full for black and white film.

Now place the spot yourself: in the simulator, switch to Spot metering in an auto mode, tap the performer on the dark stage to put the spot there, and get a good exposure.

Want to place tones one at a time with a tiny circle? Spot metering walks through it step by step.

Metering modes decide where the meter looks

A metering mode is the setting that tells the meter which part of the frame to read and how much weight to give each part. Every metering mode makes the same middle-gray assumption. What changes is which part of the frame it reads and how it weighs it. Exact areas vary by camera, so check your manual for yours.

• Matrix or evaluative: What it reads: The whole frame in many zones, compared against patterns, often weighted toward the focus point or detected faces. Good for: Everyday shooting, changing scenes, when you have no time to think. Watch out for: Hard to predict; small changes in framing can shift the result.
• Center-weighted: What it reads: The whole frame, with most of the weight (often around three quarters) given to a circle in the middle. Good for: Centered subjects; consistent readings across a series. Watch out for: An off-center subject is read as background; bright sky or dark ground at the edges still counts a little.
• Partial: What it reads: A central area of roughly 6 to 10 percent of the frame. Good for: A face or subject against a much brighter or darker background. Watch out for: Not offered on every camera.
• Spot: What it reads: A small circle of about 1 to 5 percent of the frame, at the center or at the active focus point. Good for: Placing one known tone; stages; small subjects in big contrast. Watch out for: Makes whatever it reads middle gray, including a white shirt.
• Highlight-weighted: What it reads: The whole frame, biased to keep the brightest areas from clipping. Good for: Stage light, sunlit subjects against shade. Watch out for: Leaves the rest of the frame dark; plan to lift shadows later.

Matrix is a sensible default because it was designed to spot the scenes that fool a simple average, like a bright sky over a darker landscape. It is good, but it is not a mind reader. It will still often gray down a frame full of snow, and it can still blow out a small face against a dark stage. Spot and partial are tools for scenes where you know which tone matters. Center-weighted is the predictable middle ground, and the way most film cameras metered for decades.

Center-weighted metering, up close

Center-weighted metering (also written centre-weighted, or center-weighted average) reads the whole frame but takes most of its answer from a circle in the middle. A common split is about three quarters of the weight from that circle and a quarter from everything else, and some cameras let you choose how big the circle is. It uses no scene recognition, so the same framing in the same light gives the same reading every time. That makes it useful for a run of product or catalog shots that must match, and its errors are easy to predict: a white subject filling the middle needs plus compensation, about plus 1 to plus 2, and a black one about minus 1 to minus 2.

It works best when the subject sits in the middle and the edges are much brighter or darker, such as a head-and-shoulders portrait against a bright window or a centered subject against a dark wall, because the edges count for much less. A small subject in a big frame is different: it fills too little of the circle, and the background still decides the reading. The weakness is the other side of the same coin: it meters whatever is in the center, so a subject placed off to one side gets an exposure set by whatever happens to be behind the middle of the frame. Meter with the subject centered, lock the exposure, then recompose.

Pick a mode and a sample scene below, and watch which part of the frame each mode reads and how the exposure it chooses changes.

A practical point that catches people out: on some cameras, matrix or evaluative metering with single-shot autofocus locks the exposure when you half-press, while other modes keep measuring until the shutter fires. If your exposure seems to “stick” after you recompose, that is why. When you want to choose the moment the reading is taken, use exposure lock: meter the tone you care about, press AE-L, then recompose.

Reflected readings versus incident readings

Your camera’s meter reads reflected light, so the subject’s own tone changes the reading. An incident light meter works the other way: you hold it at the subject, its white dome facing the camera, and it measures the light falling on the subject before anything reflects it. A white dress and a black suit standing side by side give the same incident reading, and the exposure it suggests renders both correctly. That is the reason studio, film and cinema photographers still carry a handheld meter.

You can get close to an incident reading without one:

• A gray card held in the same light as the subject and filling the spot or partial circle gives you a known mid tone to meter. It is a reference for that light only. It does not “calibrate” the camera, and the reading is wrong as soon as you meter a card in sun for a subject in shade.
• The Sunny 16 rule skips the meter entirely: in full sun, f/16 at a shutter speed of 1 over your ISO. At ISO 100 that is f/16 at 1/100, or the same exposure as f/8 at 1/400. Like an incident reading, it ignores the subject’s tone, which is why it handles snow and black dogs without compensation. The swan and the dog on this page were both shot within about two thirds of a stop of it.
• Your palm, metered in the same light as the subject, is a reasonable stand-in. For lighter skin, set the needle to about plus 1.

Checking the meter’s answer after the shot

The meter is a prediction made before you shoot. Several tools tell you what actually happened, and they are more trustworthy than a glance at the rear screen, whose brightness depends on its setting and the light around you.

• The histogram shows how the tones in the file are spread. A snow scene should bunch toward the right without climbing the right wall. A night street should bunch to the left.
• Highlight warnings flash the areas that have clipped to pure white. They are the fastest check when a bright subject matters.
• Zebras and the live preview on mirrorless cameras and in live view show highlight levels and a brightness preview before you press the shutter. With exposure preview on, what you see is close to the file you will get.

Two cautions. The middle of the histogram is not middle gray: in a standard sRGB file an 18 percent gray lands near 118 on the 0 to 255 scale (the encoding is not linear), and each camera’s picture style shifts it again. And the histogram and blinkies are drawn from the JPEG preview, even when you shoot raw, so a raw file usually holds a little more highlight detail than the warning suggests.

Underexposure and overexposure are not equal mistakes. A raw file a little too dark can usually be brightened later, at the cost of some noise. A highlight that clipped to pure white holds no detail at all. That is why many photographers bias tricky scenes slightly toward protecting highlights, and why exposing to the right means pushing exposure up only as far as the highlights allow.

Metering in tricky light, scene by scene

• Snow or a white beach: matrix plus 1 to plus 2, or spot on the snow and set plus 2. Check that the snow is not blinking.
• Backlit portrait: spot or partial on the face and adjust for the skin tone, or matrix plus 1 to plus 2. The bright background will clip, and that is usually fine. If you want to keep some of the background, light the face with fill flash instead. For more on light from behind, see working with backlighting.
• Fog or mist: bright and low in contrast, so the meter darkens it. Add plus 2/3 to plus 1 1/3 to keep it light and airy. Fog photography covers the rest.
• Night street: the meter tries to turn night into gray dusk. Minus 1 to minus 2 keeps it dark and protects lit signs. Watch for clipped lights on the histogram. More in night street photography.
• Stage or concert: a small lit performer on a black stage fools averaging modes into overexposing. Spot on the performer’s face or use highlight-weighted, and let the background go black. Concert photography goes further.
• Bright sky over a dark foreground: no single reading holds both. Meter for the part that matters most, or bracket and merge into HDR. The scene is wider than your camera’s dynamic range.
• A deliberately light or dark picture: the meter pulls a bright, airy frame down and a dark, moody one up. Add plus compensation for high key and minus for low key, and judge by the histogram. High key and low key photography covers both.
• Silhouette: meter the bright sky beside the subject, never the sun itself, and set the needle at zero or a little below. The subject drops to black because it is several stops darker than the sky.

In the sunset photo above, the exposure belongs to the sky. The trees are far darker than the clouds behind them, so once the sky is placed near middle gray, they fall to black with no extra work. Had the meter read the trees, it would have added several stops of light and washed the sky to white. That is the whole technique behind a silhouette: choose the tone you want to keep and let the rest follow.

Is the scene simply too bright and too dark at once for any reading? Dynamic range explains why, and what to do about it.

Backlight is where the meter most often guesses wrong. One of these two photos was metered for the subject and one for the bright background. Pick the one metered for the subject.

Which photo metered for the subject rather than the background?

A B

Common mistakes with metering

• Believing the meter measures the subject. It measures whatever is in its area. Recompose from tight to wide and the reading changes even though the subject did not.
• Expecting spot metering to be “correct”. Spot makes the spot middle gray. Spot a white shirt and center the needle, and the shirt comes out gray.
• Treating a centered needle as a good exposure. Zero means middle gray for what was read, nothing more.
• Assuming matrix knows snow is white. It is better than a plain average, but frame-filling bright or dark scenes still fool it.
• Changing metering mode in manual and expecting the photo to change. The mode moves the needle; your settings decide the exposure.
• Metering a gray card in different light from the subject. The card is only a reference for the light it sits in.
• Judging exposure from the rear screen. Use the histogram and highlight warnings instead.
• Switching metering modes for every shot. It slows you down and makes a series inconsistent. Leave one mode set, correct with compensation, and change mode only when one tone clearly matters.
• Forgetting to reset compensation or spot mode. Plus 2 for snow is a disaster in the next room. Make zero and your default mode part of the walk away.

Try this: white, black and gray in ten minutes

Find a sheet of white paper, something black with a little texture (a sweater or a camera bag), and something mid-toned (a gray card, a brown cardboard box or faded jeans). Put all three in the same even light, near a window or outside in open shade.

1. Set aperture priority, compensation at zero, and spot or center-weighted metering. Fill the frame with the white paper and shoot. Do the same with the black item, then the mid-toned one. Note the shutter speed the camera chose each time.
2. Look at the three frames together. They will all be close to the same gray, and the shutter speeds for the white and the black frames will be about four stops apart (a factor of 16), even though the light never changed.
3. Switch to manual. Meter the mid-toned item, set the needle to zero, and leave the settings alone. Now shoot all three items at that one exposure.
4. Compare. This time the paper is white, the black is black and the middle is middle. Check the histograms: the paper should sit well to the right without touching the edge, the black well to the left.

On a phone, tap the white paper to meter it and watch the screen darken, then tap the dark item and watch it brighten. That tap is a spot meter, and the sun or brightness slider next to it is exposure compensation. You have done it right if you can predict, before each tap, which way the picture will move.

Want to try the same thing with no camera in hand? The Camera Simulator lets you change settings and see the exposure move.

Want to check you can predict when the meter will miss, and which way to correct it? The camera metering quiz covers metering modes, snow, black subjects and exposure compensation.

Questions about metering

Which metering mode should I leave my camera in?

Matrix or evaluative is the most forgiving default for general shooting. Switch to spot or partial when one tone matters and the background is much brighter or darker, then switch back. Whatever mode you use, compensation and the histogram do most of the correcting.

Why did my face shot come out dark when I spot metered the face?

Because spot metering made the face middle gray, and most lighter skin sits about a stop above that. Add plus 2/3 to plus 1. For deeper skin, zero or a little minus may be right.

What is the difference between spot and partial metering?

Only the size of the circle. Spot reads about 1 to 5 percent of the frame and partial about 6 to 10 percent. Spot is more precise but a small aiming error can land it on the wrong tone; partial is a little more forgiving, which suits a face that does not fill the frame.

Does the metering mode matter in manual mode?

It changes what the needle reads, not the photo. The exposure is whatever aperture, shutter speed and ISO you set. With auto ISO in manual, the mode and compensation matter again, because the camera is choosing the ISO from the meter.

Why do the meter and the histogram disagree?

They answer different questions. The meter predicts the brightness of the area it read; the histogram shows every tone in the finished file. A snow scene metered at plus 2 should show a histogram crowded to the right, and that is correct.

Do I need a handheld light meter?

Usually not. The camera meter, compensation and the histogram cover most work. A handheld incident meter earns its place with film, studio flash and video, where you want readings that ignore the subject’s tone.

Want to see what one stop, two stops or a third of a stop really means in numbers? Exposure value puts every combination on one scale.