Sunny 16 Exposure Calculator
The Sunny 16 rule is a classic exposure guideline used by film and digital photographers when no light meter is available. In direct bright sunlight, the correct exposure is f/16 at a shutter speed of 1/ISO seconds. At ISO 200, that means 1/200 s at f/16. If you change aperture, the shutter speed adjusts by one stop for each stop of aperture change. Different lighting conditions subtract exposure value (EV) stops from the sunny baseline. This calculator takes your ISO, aperture, and lighting condition to give you the recommended shutter speed in seconds and milliseconds.
Sunny 16 formula
Shutter (s) = (f / 16)^2 / (ISO * 2^(EVoffset))
At f/16 in full sun (EV offset 0 from Sunny 16 baseline), shutter = 1/ISO. Opening aperture from f/16 to f/8 is 2 stops, so shutter becomes 1/(ISO x 4). Each EV offset step doubles or halves the required shutter time.
Lighting condition reference
- Bright snow or sand in sun: EV 16, use EV +1 offset
- Bright sun (Sunny 16 baseline): EV 15
- Slightly overcast: EV 14, one stop slower
- Overcast: EV 13, two stops slower
- Heavy overcast: EV 12, three stops slower
- Dusk or window light: EV 11, four stops slower
Sunny 16 calculator: frequently asked questions
What is the Sunny 16 rule?
The Sunny 16 rule states that in bright sunlight, the correct exposure is achieved at f/16 with a shutter speed of 1/ISO. For example, at ISO 100, use 1/100 s (or the nearest standard value, 1/125 s) at f/16.
How does aperture affect the calculation?
When you change aperture from f/16, you compensate with shutter speed. Each stop you open the aperture (e.g., f/11) doubles the shutter speed needed (halves the exposure time). This calculator adjusts automatically for any f-number.
What EV adjustments apply to different lighting conditions?
Slight overcast (open shade): subtract 1 EV (1 stop slower shutter). Overcast: subtract 2 EV. Heavy overcast: subtract 3 EV. Open shade: subtract 3 EV. Dusk/indoor bright: subtract 4-5 EV. The Sunny 16 baseline EV is 15 at ISO 100.
Why does the rule use 1/ISO as the base shutter speed?
At ISO 100 in bright sun, a correct exposure requires EV 15. At f/16, shutter 1/125 s achieves this. 1/ISO is a handy approximation because it stays within a third-stop of correct across all standard ISO values.
Is the Sunny 16 rule accurate enough for film and digital?
Yes. It is accurate to within roughly one stop, which is sufficient to place the exposure in a usable zone. It is used as a backup when a light meter is unavailable and as a sanity check for metered exposures.
Official sources
- ISO 12232:2019: Photography, Digital still cameras, Determination of exposure index. ISO.org.
- ANSI PH2.7-1986: American National Standard for Photography, Photographic Exposure Guide. Referenced by the Sunny 16 formulation. ANSI via NIST.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.