ISO Exposure Calculator
Changing ISO Means Something Else Has to Change Too
Raise ISO and a camera needs less light to produce the same exposure — but "the same exposure" only holds if shutter speed or aperture compensates for the change. This calculator handles that trade explicitly: given a shift in ISO, it computes exactly how much faster the shutter speed can go, or how much the aperture can close down, while keeping total exposure equivalent.
The Formula
New Shutter Speed = Current Shutter Speed ÷ 2^Stops (aperture held constant)
New Aperture = Current Aperture × 2^(Stops ÷ 2) (shutter speed held constant)
The aperture relationship uses a square root of the stop factor because f-numbers scale with the square root of light-gathering area — each full stop of aperture change (f/2.8 to f/4, for example) is a factor of √2 in f-number, not a factor of 2.
Where This Calculation Matters
- Low-light shooting — working out exactly how much shutter speed you gain by raising ISO, to freeze motion that a lower ISO couldn't.
- Manual mode transitions — moving from a tripod-based low-ISO setup to handheld shooting without recalculating exposure by trial and error.
- Flash and studio work — matching ambient exposure to a fixed flash-determined aperture by adjusting ISO and shutter together.
- Noise-versus-blur tradeoffs — quantifying the exact shutter speed gained by accepting a specific increase in sensor noise from higher ISO.
ISO Stops Relative to ISO 100
| ISO | Stops above ISO 100 |
|---|---|
| 100 | 0 |
| 200 | 1 |
| 400 | 2 |
| 800 | 3 |
| 1600 | 4 |
| 3200 | 5 |
| 6400 | 6 |
Going from ISO 100 to ISO 1600 (4 stops) lets you use a shutter speed 16 times faster (2⁴) at the same aperture, or close the aperture by 4 stops at the same shutter speed.
How to Use This Calculator
- Choose what to solve for: Shutter Speed or Aperture.
- Enter the current ISO and the new ISO you're changing to.
- In shutter mode, enter the current shutter speed in seconds. In aperture mode, enter the current aperture f-number.
- Select Calculate to get the equivalent-exposure setting for the new ISO.
Related Calculations
To see the full exposure value behind any settings combination, use the Camera Exposure Calculator. For how aperture also affects depth of field, not just exposure, see the Depth of Field Calculator.