Sunny 16 Exposure Calculator
Meter-free daylight exposure: the Sunny 16 rule gives you a shutter speed for any ISO, aperture and sky condition.
How it works
Shutter = (1 ÷ ISO) × (f-number ÷ 16)² × 2^(condition stops), where 1/ISO is the sunny-day speed at f/16
The Sunny 16 rule is a field trick for exposing without a meter: in bright sun at f/16, the correct shutter speed is one over the ISO. From that anchor, changing the aperture rescales the time by the square of the f-number ratio (since exposure follows the area of the aperture), and softer light adds stops — one for slight overcast, two for full overcast, and more for shade. It is remarkably reliable and is the basis every film photographer falls back on when a battery dies.
Worked example
At ISO 100 in bright sun, f/16 gives 1/100 s. Open up to f/8 (two stops brighter) and the shutter must speed up by the square of 8 ÷ 16 = 0.25, to 1/400 s to keep the same exposure.
Frequently asked questions
Does Sunny 16 still work with digital cameras?
Yes. It is a property of daylight, not of film, so it gives a solid starting exposure on any camera. Digital shooters can then chimp the histogram and fine-tune, but the rule usually lands within a stop.
What if it is not sunny?
Open the aperture by the number of stops the sky is dimmer — one stop for hazy sun, two for overcast, three for heavy cloud — or pick the matching condition here and the shutter is adjusted for you.
Why is the shutter based on ISO?
It is the rule’s clever shortcut: at f/16 in bright sun, sensor or film of a given ISO is correctly exposed at a shutter speed of one over that ISO. So ISO 200 wants 1/200 s, ISO 400 wants 1/400 s, and so on.
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This calculator is for educational purposes. Double-check important results before acting on them.