Sunny 16 rule chart

The rule and its variants

Each kind of light has a base aperture; the shutter speed is always 1 ÷ ISO. Judge the light by the shadows: the harder their edges, the brighter the sun.

Each row is one stop from the next (f/22 to f/16 is 0.92 stops, because f-numbers are rounded). The exposure values follow from EV = log₂(N² ÷ t): f/16 at 1/100 s is EV 14.6, a third of a stop below the textbook "EV 15" for full sun, which assumes 1/125 s.

Sunny 16 shutter speeds by ISO

Full sun at f/16, plus the same exposure at wider apertures. "Film dial" is the nearest full-stop speed on a mechanical camera.

Shutter speed at f/8 in every kind of light

f/8 is a common working aperture for street and travel photography. For each light, the shutter time is (1 ÷ ISO) × (8 ÷ base aperture)²:

Equivalent exposures in full sun

All of these give the same exposure as f/16 at 1 ÷ ISO. Pick the aperture for the depth of field you want and read the shutter speed:

Worked example: ISO 400 film on a sunny day

The rule gives f/16 at 1/400 s; a film camera’s nearest speed is 1/500 s. For a portrait at f/5.6 you open up three stops, so the shutter must be three stops faster: (1 ÷ 400) × (5.6 ÷ 16)² = 1/3265 s, set as 1/3200 s. If your camera tops out at 1/1000 s, solve for the aperture instead: N = 16 × √(400 ÷ 1000) = f/10.1, so use f/11 at 1/1000 s — or load ISO 100 film, which brings f/5.6 down to 1/800 s.

Looney 11: the same idea for the Moon

The full Moon is a sunlit landscape, so a similar rule works for it: f/11 at 1 ÷ ISO — f/11 at 1/100 s at ISO 100, or f/16 at 1/50 s. Expose for the Moon this way and the night sky around it goes black; a crescent Moon needs one to two stops more.

When the rule needs adjusting

• Backlit and side-lit subjects: the rule assumes the sun is behind you. For a backlit face in the shade of its own head, give one to two stops more (use the "open shade" row).
• Low sun: within an hour or two of sunrise and sunset the light is weaker even when shadows are crisp; use f/8–f/4.
• Bright surroundings: snow, sand and white walls reflect light into the shadows, so close down to f/22.
• Negative vs slide film: colour and black-and-white negative film tolerate over-exposure well — when in doubt, give more light. Slide film and digital RAW files protect highlights best when you are exact.

FAQ

What is the sunny 16 rule?

On a sunny day with hard-edged shadows, set the aperture to f/16 and the shutter speed to 1 ÷ ISO: f/16 at 1/100 s for ISO 100, 1/400 s for ISO 400. Use the nearest speed your camera offers, such as 1/125 s for ISO 100 on a film-era dial.

What are the variants of sunny 16?

Open up one stop for each step down in light: f/11 for hazy sun with soft shadows, f/8 for overcast, f/5.6 for heavy overcast and f/4 for open shade or sunset — always with a shutter speed of 1 ÷ ISO. For snow or sand in full sun, close down to f/22.

How do I use sunny 16 at a wider aperture?

Keep the exposure value the same: each full stop wider halves the shutter time. At ISO 100 in full sun, f/8 needs 1/400 s, f/5.6 about 1/800 s and f/2.8 about 1/3200 s. The general formula is t = (1 ÷ ISO) × (N ÷ 16)².

Does sunny 16 work for digital cameras?

Yes. The rule describes the light, not the medium. On digital it is a quick sanity check when the meter is fooled by a bright sky, snow or a dark subject, and on mechanical film cameras without a working meter it is often all you need, because negative film tolerates a stop or two of error.

Need the third side of the triangle? The equivalent exposure calculator solves for shutter speed, aperture or ISO from any metered setting, and the exposure triangle explained covers stops and EV.