The Sunny 16 Rule: Correct Exposure Without a Light Meter

Before light meters existed, how did photographers find their exposure? The answer came printed on the little slips of paper inside film boxes, and it fit in one sentence: in bright sun, set the aperture to f/16 and the shutter to the inverse of your ISO. This is the Sunny 16 rule — and even in the age of AI-assisted metering it’s worth learning, because it gives you something no camera ever will: the ability to read light with your own eyes.

The rule: f/16 + 1/ISO

Plain and simple: under a cloudless sky, with the sun reasonably high (roughly mid-morning to mid-afternoon), for a subject in direct sunlight:

• Aperture: f/16
• Shutter: 1 / ISO (the nearest value)

At ISO 100, f/16 + 1/125; at ISO 200, f/16 + 1/250; at ISO 400, f/16 + 1/500. That’s all. No metering, no histogram, no test frame — on a sunny midday these settings drop you within a whisker of correct exposure, every time.

If that sounds too simple, let’s look at why it works.

Why it works: the sun is a remarkably consistent lamp

The distance between us and the Sun is so vast that the intensity of light reaching the ground on a clear day barely changes from day to day or city to city. A July noon in Istanbul and a June noon in Berlin are, exposure-wise, the same lamp. Scenes change; the light doesn’t.

Your camera’s meter works on the opposite principle: it reads the light reflected off the subject and assumes every scene averages out to middle grey. That’s why it darkens snow toward grey and brightens a black cat toward grey — the systematic bias we covered in the exposure compensation guide.

When the weather changes: read the shadow, shift the aperture

The rule isn’t only for blazing sun; you read the sky and slide the aperture. The shutter stays fixed at 1/ISO — the only thing that moves is the f-number, and the most reliable gauge is the quality of the shadows on the ground:

• Harsh sun on snow or pale sand → f/22 (the ground bounces extra light onto the subject; close down a stop)
• Bright sun, crisp dark-edged shadows → f/16 (the rule’s home)
• Slightly overcast, shadow edges gone soft → f/11
• Overcast, shadows barely visible → f/8
• Heavy overcast, no shadows at all → f/5.6
• Subject in open shade, or close to sunset → f/4

You don’t have to shoot at f/16: equivalent exposures

What the rule gives you isn’t a fixed pair of settings but an amount of light. f/16 + 1/125 + ISO 100 is just the starting point; you can trade stops to convert the same light into whatever character you want:

• f/16 — 1/125 → a landscape that wants deep focus
• f/8 — 1/500 → everyday shooting, the street sweet spot
• f/4 — 1/2000 → a motion-freezing sports frame
• f/2.8 — 1/4000 → a shallow portrait (mind your shutter ceiling in daylight)

Every line produces the same brightness; the difference is which rung of the f-stop ladder you start from. Think of Sunny 16 not as “the f/16 rule” but as “the sunny-day exposure value”: it anchors the light, and you slide around the triangle from there.

The Moon’s cousin: Looney 11

The rule has a lesser-known relative: the full moon in the middle of the night is also a sunlit surface, so it has its own rule — f/11 + 1/ISO. The details, and the full “the Moon is not a night subject” lesson, are in the moon photography guide. The two rules are children of the same idea: when the light source is constant, exposure can be memorized.

Where it fails: the rule’s honest limits

Sunny 16 is a daylight rule, and knowing its limits matters as much as knowing the rule:

• Low sun: During golden hour the light both changes fast and travels a long path through the atmosphere — the rule collapses stop by stop; near sunset you’re down to f/4, and minutes later even that is stale.
• Indoors and at night: The source is no longer the sun; the constant lamp the rule depends on is gone. Here metering and the histogram take over.
• Harsh mixed light: In a scene half in sun, half in shade, the rule only lets you choose which half to sacrifice — that’s not a flaw, it’s the nature of exposure.
• Very low winter sun: At high latitudes the winter sun is weak even at noon; opening up half a stop to a stop may be needed.

Who needs this rule in 2026?

With hardly a meterless frame shot anymore, four real scenarios keep Sunny 16 alive:

1. Meterless film cameras: On analog bodies with a dead battery or no meter at all, the rule is your only exposure tool — it’s why film shooters still know it by heart.
2. Scenes that fool the meter: In snow, on the beach, against backlight, the meter pulls toward grey; Sunny 16 doesn’t. If the meter’s suggestion sits two stops from the rule, the one that’s wrong is probably the meter — the rule is a lie detector you carry in your pocket.
3. Manual-mode training: Shooting by the rule forces you to think about exposure before the camera does. Play “guess first, then meter” for a few weeks: when your guesses start landing within a stop of the meter, your exposure intuition has become permanent.
4. Understanding light: A photographer who can think “a cloud came over, I just lost a stop” moves all three arms of the exposure triangle deliberately. The rule is the multiplication table of light literacy.

Common mistakes

• Applying the rule at golden hour: Sunny 16 is a high-sun rule; open up stop by stop as the sun drops, and abandon it entirely at sunset.
• Changing ISO and forgetting the shutter: The rule’s two halves are linked — if you moved to ISO 400, the shutter must move to 1/500, or the frame blows out by two stops.
• Staying at f/16 in snow: Snow and pale sand bounce light up onto the subject; without closing a stop (f/22, or one shutter step faster) the snow detail burns away.
• Expecting laboratory precision: Sunny 16 drops you in the right neighbourhood; your RAW margin and the histogram find the exact door. A half-stop drift is the weather’s character, not the rule failing.
• Judging the sky instead of the shadow: Estimating cloud cover by eye misleads; the sharpness of the shadow at your feet is a far more reliable light thermometer.