Exposure Calculator

Calculator for the ISO Exposure Equation.

$\frac{N^{2}}{t} = \frac{L S}{K}$

Enter values for three of the four main exposure variables: Relative Aperture, Exposure Time, Average Scene Luminance, and ISO Speed. The default value for Meter Calibration Constant is 12.5.

Note: For Exposure Time you may enter seconds (e.g. "0.02"), milliseconds (e.g. "200ms"), or a fraction (e.g. "1/50").
For Aperture you may enter a decimal (e.g. "3.2") or use the "base+fraction" format (e.g. "2.8+1/3").

Relative Aperture (N):

Exposure Time (t):

Note: For Average Scene Luminance you can either enter the luminance directly (in cd/m²) or leave it blank and instead supply the Scene Illuminance (in lux) plus the Average Scene Reflectance (in percent, default is 16%, see here). If a luminance value is entered, the illuminance/reflectance inputs are ignored.

Average Scene Luminance (L): cd/m²

Scene Illuminance (E): lux

Average Scene Reflectance (R): %

ISO Speed (S):

Meter Calibration Constant (K):