How to use the equivalent exposure calculator
- Enter the aperture (the number after f/), the shutter speed such as 1/125, and the ISO of your settings.
- Choose which setting to keep fixed: ISO, aperture or shutter speed.
- Choose the step size: full stops, half stops or third stops. Open More options to change how many stops the table covers each way.
- Read the table. Every row has the same exposure as your settings, which are highlighted in the middle.
Formula
EV (at ISO 100) = log2(N^2 / t) - log2(ISO / 100)
one stop narrower aperture = N x sqrt 2 and lets in half the light
one stop slower shutter = t x 2 and lets in twice the light
N is the f-number and t the shutter time in seconds. Every row keeps EV the same. The table shows exact values and the nearest value marked on a camera, because cameras label f/5.6 for 5.657 and 1/125 for 1/128.
f/8, 1/125 s, ISO 100
The exposure value is log2(64 x 125) = 12.97 at ISO 100. Keeping ISO 100, the same exposure is f/4 at 1/500, f/5.6 at 1/250, f/11 at 1/60 and f/16 at 1/30, because each stop of aperture is traded for a stop of shutter time.
Keeping the aperture at f/8, the equivalents are 1/500 at ISO 400, 1/250 at ISO 200 and 1/60 at ISO 50. Another set, f/2.8 at 1/60 and ISO 400, has an exposure value of 6.88.
The exposure triangle
Aperture, shutter speed and ISO together set how bright the picture is. If you change one, you must change another in the opposite way to keep the same brightness. The table makes these trades for you in steps of whole, half or third stops.
Equal exposure does not mean an equal picture. A wider aperture gives a shallower depth of field, a slower shutter blurs motion and a higher ISO adds noise. Choose the setting to keep fixed by what matters most for the shot. To see how aperture changes the zone in focus, use the Depth of Field Calculator.
Filters and long exposures
A neutral density filter cuts light by a known number of stops, so you can treat it as a change in exposure. The ND Filter Exposure Calculator works out the new shutter time. Very long exposures may need more time than the table shows because of reciprocity effects in film, which this page does not model. The Crop Factor Calculator relates apertures and focal lengths across sensor sizes.
More hobby and sport tools
For other hobbies, sports and music, try the Key Finder, Maidenhead Locator Converter and Poker Chip Distribution Calculator.
Assumptions and limits
- The scene lighting does not change, and the meter reading you started from was right.
- Aperture values are f-numbers, and shutter speeds are in seconds (1/125 means 0.008).
- Full stops change the light by a factor of 2; half and third stops by the square root and cube root.
- Nominal values in the table are the nearest marked values and may differ slightly from the exact ones.
Frequently asked questions
What is EV?
Exposure value is a single number for the combination of aperture and shutter speed at ISO 100. A higher EV means a brighter scene or less light let in. Equivalent settings share one EV.
Why is f/5.6 written when the exact value is 5.657?
The marked numbers are rounded to two digits for convenience. The table shows the exact values for calculation and the marked values you set on a lens.
How do I enter a shutter speed longer than a second?
Write it in seconds, such as 2 or 30. You can add an s. Fractions such as 1/2 and decimals such as 0.5 also work.
What does the step size change?
Full stops give coarse rows, and third stops give rows for the in-between settings most cameras allow. The exposure is the same in every row either way.