Photography Calculators

Exposure & light

Exposure Value Calculator

EV is the single number a handheld meter shouts. The aperture/shutter pair alone, log2(N²/t), is the EV at the ISO you set. EV100 refers that same light back to ISO 100, so it sits one lower for every stop of ISO above 100. Same scene, same light — settings that expose it correctly at different ISOs all give the same EV100.

Inputs

Units
f/

Taking f-number.

s

Time in seconds. 1/100 is 0.01, 1/250 is 0.004.

Working ISO, not the camera’s dual-gain sweet spot unless that is what you set.

Results

EV at ISO 100
12.64

Light level referred to ISO 100; Sunny 16 is about 15 at any ISO.

EV at working ISO
12.64

log2(N²/t) at your ISO; above ISO 100 it is higher than EV100.

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Example products

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Calculation method

EV at your working ISO is the base-2 log of f-number squared divided by shutter time in seconds; that is all the aperture/shutter pair can say. EV100 refers the same light to ISO 100 by subtracting log2(ISO/100): a higher ISO needs less light, so the same settings suit a darker scene. Two settings with the same EV100 give the same image brightness of one scene, and Sunny 16 is about EV100 15 whatever ISO you shoot it at. A one-stop change in aperture or shutter moves both numbers by one; a one-stop ISO change moves only EV100.

Exact formula

EV_ISO = log2(N²/t). EV100 = log2(N²/t) − log2(ISO/100), so EV_ISO = EV100 + log2(ISO/100). Limits: Incident vs reflected, ND, flash contribution and metering pattern omitted; it is the photographic triangle only.

Video people

Cinematographers often talk 180° shutter and T-stops. Convert angle to time with the shutter-angle calculator, then drop that time in here as shutter seconds.

Log profiles

A log picture profile does not change EV. It changes how the file is encoded. Expose for the highlight budget of that profile, then map EV as usual.

Frequently asked questions

Is EV100 what my meter shows?

Depends on the meter. Some always show EV at ISO 100; compare that with EV100 here. Others show EV at the ISO you dialled; compare that with EV at working ISO. The two differ by log2(ISO/100), two stops at ISO 400, so do not mix them.

Why isn’t 1/100 at f/8 ISO 100 equal to 15?

Sunny 16 is f/16 at 1/ISO, which is EV 15. f/8 at 1/100 is two stops more exposure than f/16 at 1/100, so EV 13. The numbers only look ‘off’ if you expected sunny 16.

Does an ND filter change EV?

On the sensor, yes — you need more time or ISO. This calculator does not know about filters. Add the ND stops on the ND calculator, then come back.

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