Calculate Exposure Value (EV) from ISO, aperture, and shutter speed.
Calculator verified • Last updated: August 2026
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EV combines aperture and shutter speed, normalized to ISO 100 — any combination of settings that produces the same EV gives the same overall exposure.
Exposure Value combines aperture and shutter speed into one number, then adjusts for ISO. A narrower aperture (larger f-number) or a faster shutter speed (larger denominator, shorter time) both raise EV; a higher ISO lowers it, since less light is needed at higher ISO for the same result.
$$EV = \log_2\left(\frac{N^2}{t}\right) - \log_2\left(\frac{ISO}{100}\right)$$
N: aperture (f-number).
t: shutter time, in seconds — equal to 1 divided by the entered denominator.
ISO: sensor sensitivity setting.
At ISO 100, f/8, and a shutter speed of 1/125 second: N squared is 64, divided by t (1/125, or 0.008 seconds) gives 8,000; log base 2 of 8,000 is about 12.97. Since ISO is exactly 100, the ISO term is zero, so the exposure value works out to about EV 12.97 — a typical outdoor daylight exposure.
Because EV combines all three settings, different combinations can produce the identical EV and therefore the identical overall exposure. Doubling ISO effectively doubles sensitivity, so the shutter time can be cut in half (shutter speed denominator doubled) at the same aperture and still land on the same EV — useful for freezing motion in lower light without opening the aperture further, at the cost of more noise from the higher ISO.
Confusing the shutter speed denominator with the actual time is a frequent source of error — a "shutter speed of 250" means 1/250 second, not 250 seconds, and typing the raw denominator anywhere a time value is expected inverts the result.
Assuming EV alone determines whether a photo looks correctly exposed is another — EV describes the camera's settings, not the scene's actual light level. The same EV can look correctly exposed for one scene and badly over- or under-exposed for another with different actual brightness; EV needs to be matched to the scene's metered light, not treated as a universal target.
Exposure Value (EV) — a single number combining aperture and shutter speed (normalized to ISO 100) that describes how much light a given combination of settings lets through.
Stop — a doubling or halving of light; each whole EV step, and each full ISO/aperture/shutter adjustment on a standard scale, represents one stop.
Reciprocity — the principle that aperture, shutter speed, and ISO trade off against each other to produce the same total exposure, which is what makes equivalent-exposure combinations possible.
Exposure Value (EV) is a single number that combines aperture and shutter speed (normalized to ISO 100) into one measure of how much light reaches the sensor. Different combinations of aperture and shutter speed that produce the same EV result in the same overall exposure.
Equivalent exposure means different combinations of ISO, aperture, and shutter speed that all produce the same EV and therefore the same overall brightness — for example, doubling ISO lets you use a shutter speed twice as fast (half the exposure time) while keeping the same exposure.
A higher EV number corresponds to less light reaching the sensor per the settings used (a narrower aperture and/or a faster shutter speed) — EV is a measure of the camera's exposure settings, not the scene's actual brightness, though the two are linked when correctly exposing a given scene.