Sunny 16 Calculator — Quick Exposure Estimates

On a sunny day with distinct shadows, set your aperture to f/16 and your shutter speed to 1/ISO. For example, at ISO 100, use f/16 at 1/100s. Adjust the aperture for different lighting conditions: f/11 for slight overcast, f/8 for overcast, f/5.6 for heavy overcast, f/4 for shade.

It is surprisingly accurate for outdoor daylight photography, typically within half a stop of a meter reading. It has been used reliably since the early days of photography and remains useful as a quick sanity check even with modern metering systems.

Yes, but there are two distinct ways to do it. (a) DIMMER light: when conditions are cloudier, open the aperture and keep the shutter at 1/ISO — this is what the calculator does when you pick f/11, f/8, f/5.6 or f/4, because the wider aperture compensates for the weaker light. (b) SAME light, equivalent exposure: in the same bright sun you can trade aperture for shutter — open one stop and halve the time, so f/16 at 1/100s equals f/11 at 1/200s, f/8 at 1/400s and f/5.6 at 1/800s. Case (a) changes the lighting assumption; case (b) keeps the total exposure identical while changing depth of field or motion blur.

Yes, though the UK often has softer light than tropical regions. In typical British conditions, you might find yourself using f/11 or f/8 more often than f/16. The rule still provides an accurate starting point.