Sunny 16 Calculator | Expose Film Without a Light Meter
Shoot a meterless film camera with confidence: pick a lighting condition, your ISO and an aperture, and get the shutter speed that lands a correct exposure. Five conditions cover bright sun through open shade, and the exact exposure time updates as you open or close down.
💡 About this tool
Plenty of classic film cameras have no built-in meter, or the old meter has long since died. The Sunny 16 rule is the field trick that fills that gap: in bright sun, set f/16 and a shutter speed equal to the reciprocal of your film speed (1/100 for ISO 100, which rounds to 1/125 on most dials).
This calculator starts from the base aperture for the condition you choose — f/16 sunny, f/11 slight overcast, f/8 overcast, f/5.6 heavy overcast, f/4 open shade or sunset — and re-times the exposure for whatever aperture you actually want to shoot. Open up one stop and the shutter has to speed up one stop; the tool handles that reciprocity with exposure = (1 / ISO) × (chosen f-stop ÷ base f-stop)², so you never count stops in your head. It also rounds to the nearest standard shutter step (1/125, 1/250 and so on) and shows the scene's EV at ISO 100.
Because the rule is built on incident light rather than reflected light, it sidesteps the metering errors that very bright or very dark subjects cause — snow, a black cat, or a backlit portrait won't fool it the way an in-camera meter would.
🧐 Frequently asked questions
Does Sunny 16 work for both negative and slide film? Negative film has wide latitude, so the rule's estimate gives clean results even if you are a stop off. Slide (reversal) film has narrow latitude and shows exposure errors immediately, so meter carefully for slides when the shot matters.
How do I tell sunny from overcast? Read the shadows. Hard-edged, dark shadows mean bright sun (f/16); slightly soft shadows mean slight overcast (f/11); diffuse shadows mean overcast (f/8); barely any shadow means heavy overcast (f/5.6).
What about snow or a bright beach? Highly reflective snow or sand adds roughly a stop of light, so stop down further (around f/22) or use a one-stop faster shutter than the sunny value. The aperture menu includes f/22 for exactly this.
Why is the shutter speed rounded? The exact exposure time is continuous, but real shutters only offer fixed steps (1/125, 1/250, and so on). The recommended value is rounded to the nearest standard step, and the exact time is shown separately.
What does the EV figure mean? EV at ISO 100 is a single number for how bright the scene is. Any aperture-and-shutter pair with the same EV gives the same exposure, which is why you can trade one for the other.
📚 Why the same f/16 works everywhere on Earth
Midday direct sun delivers roughly the same intensity — about 100,000 lux — whether you are in Brooklyn, Tokyo or Nairobi, which is why a single rule travels so well. That global constant is what let film boxes print one little exposure chart that worked for everyone. Carry a meterless rangefinder or a plastic toy camera and the math here is the same back-of-the-hand estimate photographers leaned on for decades; it has simply moved from the inside of a film box to your screen.