Exposure Stops Calculator
See the net exposure change in stops when you move aperture, shutter speed and ISO from one setting to another — brighter or darker, and by how much.
How it works
aperture stops = 2·log₂(f_from ÷ f_to) · shutter stops = log₂(t_to ÷ t_from) · ISO stops = log₂(ISO_to ÷ ISO_from) · net = sum · light factor = 2^net
A "stop" is one doubling or halving of the light reaching the sensor, and every exposure control is measured in the same stops so they trade off cleanly. Aperture is the odd one out: because the f-number is a ratio of focal length to aperture diameter and light scales with area, one stop is a change of √2 in the f-number — which is why the stop change carries a factor of two on the logarithm. Add up the stop change from each of the three controls and you get the net brightness shift; a positive result is a brighter image, and you can cancel it out by moving another control the opposite way to keep the exposure balanced.
Worked example
Opening from f/8 to f/4 is 2 × log₂(8 ÷ 4) = 2 × 1 = +2 stops of light. If shutter and ISO are unchanged, the net is +2 stops, meaning the sensor gets 2² = 4× the light — so you would shorten the shutter by two stops (e.g. 1/125 s → 1/500 s) to keep the same exposure.
Frequently asked questions
Why does aperture have a factor of 2 but shutter and ISO do not?
Light passing the lens scales with the aperture area, which goes as the square of the diameter, while the f-number is inversely proportional to diameter. That squares into a factor of two on the log, so one stop is a √2 change in f-number, not a doubling.
What does a positive result mean?
Positive stops mean a brighter image — more light reaches the sensor. Negative means darker. To keep exposure constant, offset a change on one control with an equal and opposite change on another.
How is this different from an EV calculator?
An EV calculator gives a single exposure value for one set of settings. This one compares two sets and reports the difference between them in stops, which is what you need when adjusting settings on the fly.
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This calculator is for educational purposes. Double-check important results before acting on them.