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Exposure Value (EV) Calculator

Find the exposure value of a camera setting.

How it is calculated

The tool computes two numbers:

EV = log2(N² / t) and EV100 = EV − log2(ISO / 100)

N is the f-number (aperture), t is the shutter time in seconds, and ISO is the sensitivity. The first value is the EV for the aperture and shutter pair; the second restates it as if the ISO were 100, which is the usual way light levels and exposure tables are quoted. Both must have aperture and shutter above zero or nothing is shown. If ISO is left empty or is not positive, 100 is assumed. Results have two decimals; one EV step equals one stop.

Worked example

Aperture f/8, shutter 1/125 s (enter 0.008), ISO 400.

  1. N² = 64, and 64 / 0.008 = 8000
  2. EV = log2(8000) ≈ 12.97
  3. ISO 400 is two stops above 100, so EV100 = 12.97 − 2 = 10.97

The scene light level is about EV 10.97 at ISO 100.

Try this example →

Common mistakes

  • Typing the shutter as 125 or 1/125: the field wants seconds, so enter 0.008. A fraction such as 1/125 is not understood and gives no result.
  • Comparing the plain EV of shots taken at different ISOs: the first value includes the ISO you entered, so compare EV100 instead.
  • Entering the aperture as the lens size in millimetres: use the f-number, such as 2.8 or 8.
  • Forgetting that a higher EV means less exposure (a brighter scene or a faster setting), not more light in the camera.

About this calculator

This calculator computes exposure value (EV) from aperture (f-stop), shutter speed, and ISO using EV = log₂(N²/t), then normalizes it to ISO 100 with an ISO correction term, following the standard APEX (Additive System of Photographic Exposure) system used since the 1960s.

Photographers use EV to compare exposure settings across different aperture/shutter/ISO combinations that all produce the same brightness, to apply the "sunny 16" rule and exposure tables, or to match settings between cameras. Enter the aperture, shutter speed, and ISO to get the exposure value.

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