What is the Sunny-16 rule?

On a bright sunny day, set your aperture to f/16 and your shutter speed to the reciprocal of your ISO. At ISO 100 that is f/16 at 1/100 s, which gives a correct exposure for front-lit subjects without a meter.

How does the rule change for cloudy weather?

Each step toward cloudier conditions opens the aperture one stop: slight overcast is f/11, overcast f/8, heavy overcast f/5.6, and open shade f/4. The shutter stays near one over the ISO.

What about snow or sand?

Highly reflective scenes like bright snow or white sand bounce extra light, so close down one stop to f/22, often called Sunny-22. This prevents the whites from blowing out.

Can I swap aperture for shutter speed?

Yes. The equivalent exposure list keeps brightness constant while trading aperture for shutter. Use a wider aperture for shallow depth of field or a faster shutter to freeze motion, adjusting the other to match.

Is Sunny-16 accurate enough?

For negative film and digital with latitude it is reliably close, often within half a stop. Slide film and tricky backlight benefit from a real meter, but Sunny-16 is an excellent fallback and a great way to learn exposure.

Sunny-16 Exposure Rule Calculator

Before light meters, photographers exposed by eye using the Sunny-16 rule. It still works: on a bright day, f/16 at one over your ISO gives a correct exposure. This calculator extends the rule across seven common lighting conditions and lists equivalent settings so you can shoot confidently without metering.

How it works

The base rule fixes the shutter at the reciprocal of the ISO and sets the aperture by the light:

Bright sun: f/16, shutter ≈ 1 ÷ ISO

Each cloudier condition opens the aperture one full stop, letting in twice the light to compensate for the dimmer scene:

Condition	Aperture
Bright snow or sand	f/22
Bright / hard sun	f/16
Slight overcast	f/11
Overcast	f/8
Heavy overcast	f/5.6
Open shade / sunset	f/4
Golden hour	f/2.8

Once the base aperture and shutter are set, the tool holds the exposure value constant (N² ÷ t) and lists every equivalent aperture and shutter pair, so you can trade depth of field for motion control freely.

Example and tips

At ISO 400 on a lightly overcast day, the rule gives f/11 at about 1/400 s. Want a blurred background instead? Open to f/2.8 and the equivalent list pushes the shutter to roughly 1/6400 s — same brightness, shallow focus.

Remember the rule assumes front lighting. Backlit or strongly side-lit subjects need one to two extra stops of exposure, and very reflective scenes like snow need one stop less. Treat Sunny-16 as a dependable starting point and bracket when the light is unusual.