Calculator
Exposure Calculator
Enter a correctly exposed baseline, then change ISO and/or aperture to see the shutter speed (or whichever setting you pick) needed to keep the exposure equivalent.
Original (correctly exposed) settings
New settings
Result
New shutter speed
1/122
This keeps the total exposure equivalent to your original settings — the same amount of light reaches the sensor, just distributed differently across ISO, aperture, and shutter speed.
The exposure triangle
Every exposure is controlled by three settings, and they trade off against each other:
- ISO — sensor sensitivity. Higher ISO needs less light, but adds noise.
- Aperture (f-number) — how wide the lens opening is. A lower f-number lets in more light, and also produces a shallower depth of field.
- Shutter speed — how long the sensor is exposed. Slower shutter speeds let in more light, but risk motion blur or camera shake.
"Equivalent exposure" means changing two of these settings together so the total amount of light reaching the sensor stays the same, even though each setting is doing something different to the final look of the photo.
Why this is useful
Say you metered a shot at ISO 100, f/2.8, 1/250s for a shallow-depth-of-field portrait. Now you want f/8 instead, to keep a group shot sharp front-to-back. Without recalculating, you'd either underexpose the shot or need to guess a new shutter speed. This calculator does that math for you instantly, for any two of the three settings.
How to use this calculator
Enter your original, correctly-exposed settings. Choose which setting you want to solve for — usually shutter speed, since ISO and aperture are more often the creative choices you're making on purpose. Enter your new values for the other two settings, and the calculator returns the setting you need to keep the exposure equivalent.
FAQ
Does "equivalent exposure" mean the photo will look identical? No — the brightness will match, but depth of field (from aperture), motion blur (from shutter speed), and noise level (from ISO) will all be different. Equivalent exposure only balances the amount of light, not the creative side effects of each setting.
Why enter shutter speed as a fraction like "1/250"? That matches how shutter speed is displayed on virtually every camera. For exposures of a full second or longer, just enter the number of seconds (e.g. "2" for 2 seconds).