About the Sunny 16 rule
The Sunny 16 rule is a decades-old rule of thumb: on a bright sunny day, setting your aperture to f/16 and your shutter speed to roughly 1/ISO gives a correctly exposed photo. Its lesser-known variants extend the same idea to overcast and shaded conditions at wider apertures (f/11, f/8, f/5.6, f/4). This calculator applies the same stop-for-stop math our exposure triangle calculator uses to adjust the baseline for whatever ISO and aperture you actually want to shoot at.
How the calculation works
For each lighting condition the calculator starts from a baseline aperture (sunny f/16, slight overcast f/11, overcast f/8, heavy overcast f/5.6, open shade or sunset f/4) with a shutter speed of about 1/100 s at ISO 100. It then recalculates the shutter speed, stop for stop, for the aperture and ISO you choose.
Opening the aperture by one stop halves the shutter time, and so does raising ISO by one stop. The calculator applies both in turn to reach the final value.
Worked examples
- In sunny conditions (f/16) at ISO 100 and f/16, the shutter speed is about 1/100 s. This is the classic Sunny 16 rule.
- In sunny conditions at ISO 400 and f/8, it is about 1/1600 s. Opening two stops and raising ISO two stops makes the shutter four stops faster.
- In sunny conditions at ISO 100, opening to f/5.6 gives about 1/800 s. It shows how fast the shutter has to be when you open up for a blurrier background.
- On an overcast day (f/8) at ISO 400 and f/2.8, the result is about 1/3200 s.
- In open shade (f/4) at ISO 100 and f/4, it is about 1/100 s, and at ISO 800 with f/2 it is about 1/3200 s.
When to use it
Use it as a quick reference with film cameras that have no meter, when shooting in manual exposure, or when your camera's auto exposure looks off. It is also good practice to memorize rough starting values for each lighting condition before heading outdoors.
Limits and common mistakes
- The values are estimates for typical outdoor daytime light. They may not hold for low sun in the morning or evening, strong reflections from snow or sand, or backlit scenes.
- If your subject is unusually dark or bright, check with your camera's meter or a test shot and apply exposure compensation if needed.
- Choosing the wrong lighting condition shifts the result by a stop or two. Judging by how sharp the edges of shadows are can help.
- If the shutter speed comes out too slow, camera shake can appear. Raise ISO or open the aperture.
- The displayed shutter speed is rounded to a near standard step. On a real camera, pick the closest available value.
Guides that pair well with this calculator
An estimate for typical outdoor daylight conditions — always check your camera's meter or a test shot when it matters.
Frequently Asked Questions
Does the Sunny 16 rule still matter with modern light meters?+
It's mainly useful as a sanity check, for manual-exposure film cameras without a working meter, or when you want a fast starting point before fine-tuning.
Why do the overcast variants use different apertures?+
Each stop of the aperture roughly corresponds to a lighting condition letting in about half as much light as the one before it, so the rule widens the aperture by one stop per condition to keep the same shutter speed reasonable.
What if I want a specific shutter speed instead of a specific aperture?+
Pick the aperture that gives you a shutter speed close to what you want — since the underlying math is stop-for-stop, you can also work backward from a target shutter speed using our exposure triangle calculator.