The Sunny 16 rule: in bright sun, set f/16 and the shutter speed to 1/ISO (ISO 100 → 1/100s at f/16) for a correct exposure without a meter. The scale for other conditions and how to use it in practice are below.
Quick Summary
- The Sunny 16 Rule is a guideline for setting exposure in bright sunlight without a light meter.
- The basic principle: set the aperture to f/16 and the shutter speed to the reciprocal of the ISO.
- For example, with ISO 100, use a shutter speed of 1/125s (the closest standard speed to 1/100).
- For other lighting conditions, keep the shutter speed the same and adjust the aperture (see the chart and calculator below).
- It was useful before built-in light meters became standard, and still has practical uses for film cameras without working meters and as a sanity check on modern cameras.
The Sunny 16 Rule turns up on photography T-shirts, mugs, and even the occasional bumper sticker. But one place it doesn’t turn up much anymore is when actually taking photos.
That wasn’t always the case. The rule was a staple of teaching photography back when built-in light meters weren’t yet universal, and it featured prominently in guides like Kodak’s ubiquitous (and remarkably useful) field pamphlets. These days it’s mostly a curiosity — but it still has its uses, and it’s worth knowing if you shoot film, use older cameras with broken meters, or just want a sanity check on what a modern camera’s meter is telling you.
The rule itself goes:
In bright sunlight, set the aperture to f/16 and the shutter speed to the reciprocal of the ISO.
So with ISO 100 film (or sensor setting), you’d use 1/125s — the closest standard shutter speed to 1/100.1 It replaced two earlier systems: the American ASA scale (arithmetic — doubling the number means doubling the sensitivity) and the European DIN scale (logarithmic — adding 3° means doubling the sensitivity). The “200/24°” notation you sometimes see on older film boxes pairs the arithmetic ISO/ASA value with its logarithmic DIN equivalent. Both numbers describe the same sensitivity.))
The “reciprocal” part sounds technical, but it’s really not. Just put “1/” in front of the ISO and round to the nearest standard shutter speed your camera offers:
- ISO 100 → 1/125s (closest standard speed)
- ISO 200 → 1/250s
- ISO 400 → 1/500s (closest standard speed)
- ISO 800 → 1/1000s (closest standard speed)
And so on. The reason it’s not always exact is that camera shutter dials have traditionally moved in 1-stop increments — 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000 — so the closest available speed is sometimes a touch faster or slower than the strict reciprocal.
Adjusting for different lighting conditions
Sunny 16 is really just a baseline, and an approximate one at that. Most photographs aren’t taken in cloudless midday sun. The rule extends naturally to other lighting conditions by keeping the shutter speed fixed at the reciprocal of the ISO and opening the aperture to compensate for less light.
Sunny 16 chart
| Scene Lighting | Aperture |
|---|---|
| Bright sun on snow or light sand | f/22 |
| Bright sun with distinct shadows | f/16 |
| Hazy sun (soft shadows) | f/11 |
| Cloudy bright (no shadows) | f/8 |
| Heavy overcast | f/5.6 |
| Open shade (subject in shade, lit by open sky) | f/5.6 |
| Backlit subject in bright sun | f/5.6 |
| Sunset / golden hour | f/4 |
Each row drops the aperture by roughly one stop from the row above (give or take, since f-stops aren’t perfectly linear). For all of these, you’d keep your shutter speed at 1/ISO.
The rule has obvious limits. It gives you no control over depth of field — if you want shallower focus, Sunny 16 doesn’t help directly. And for fast-moving subjects that need a faster shutter speed, you’d need to recalculate the equivalent exposure (open the aperture by the same number of stops you’ve made the shutter faster). At that point the rule has stopped being a useful shortcut and started being a way to do basic exposure math in your head.
Sunny 16 calculator
Pick your ISO and the lighting condition, and the calculator returns the suggested aperture and shutter speed. As above, these are starting points — actual conditions vary, and you’ll want to bracket exposures (or take a test shot if you’re shooting digital) to confirm.
Is the Sunny 16 Rule still useful?
The Sunny 16 Rule is a throwback to early film SLR days. Built-in light meters became standard from roughly the mid-to-late 1960s onward, and they’ve been universal in digital cameras from the start. So for most modern photography, the camera’s meter handles the job better than any rule of thumb can.
That said, it does still come up in a few legitimate situations:
- Older film cameras without meters. Cameras like the Leica M3, Nikon F (without the Photomic head), Pentax K1000 with a dead battery, or any number of vintage rangefinders and SLRs. Sunny 16 is the working photographer’s fallback.
- Cameras where the meter is broken or unreliable. Old selenium meters that have lost sensitivity, or CdS meters with mercury battery issues, can give wildly wrong readings. The rule lets you keep shooting.
- Pinhole and large-format cameras. Many of these have no meter at all, by design.
- As a sanity check on your modern camera. If your meter is suggesting an exposure that seems wildly off — usually because of an unusual scene with mostly very bright or very dark tones — Sunny 16 gives you a back-of-the-envelope check on what the right ballpark is.
- As a way to learn the relationships between aperture, shutter, and ISO. Working through Sunny 16 mentally builds intuition about how exposure works, which is useful even if you never actually shoot meterless.
So it’s not just a curiosity, even if it isn’t an everyday tool for most photographers anymore.
And it does still make for a pretty good T-shirt.
Notes & References:
- ISO is the modern international standard for film and sensor sensitivity, published in 1974 as ISO 6 and refined over the following decades. ((https://en.wikipedia.org/wiki/Film_speed [↩︎]
