Enter the f-number and the exposure time (shutter speed) into the calculator to determine the exposure value.

Exposure Value Formula

The following formula is used to calculate an exposure value.

EV = log2 (N2 / t )

  • Where EV is the exposure value
  • N is the f-number value
  • t is the exposure time/shutter speed (seconds)

Exposure Value Definition

What is an exposure value?

Exposure value is a metric used in photography that represents a combination of f-number and shutter speed such that all combinations that yield the same exposure have the same exposure value.

Example Problem

How to calculate an exposure value?

  1. First, determine the f-stop/f-number value.

    In this example, the f-number is 3.

  2. Next, determine the total exposure time.

    The exposure time for this example problem is measured to be 1.23 seconds.

  3. Finally, calculate the exposure value.

    Using the formula above, the exposure value is calculated to be:
    EV = log2 (N2 / t )
    EV = log2 (3^2 / 1.23 )
    EV = 2.871