Exposure Value Calculator

Enter the f-number, shutter time and ISO to get the exposure value (EV) and EV100. From an EV100 you can also find the f-number or the shutter time.

What do you want to find?

F-number

Shutter time (seconds; a fraction such as 1/125 is allowed)

ISO

Decimal places of the EV

EV (exposure value at that ISO) —

EV and EV100
EV (at the ISO you entered)	—
EV100 (converted to ISO 100)	—

F-number
F-number	—

Shutter time
Shutter time (seconds)	—
As a fraction	—

EV = log₂(N² ÷ t) (N: f-number, t: shutter time in seconds), and EV100 = EV − log₂(ISO ÷ 100). At ISO 100, EV = EV100. EV is a number for a combination of camera settings, not the brightness (luminance or illuminance) itself.

F-numbers such as 2.8 and 5.6 are rounded labels. The tool calculates with the number you type, so the EV is not exactly a whole number (for example, f/2.8 at 1 second gives about 2.97).

EV (exposure value) and EV100

EV (exposure value) expresses a combination of aperture (f-number) and shutter time as a single number, on a base-2 logarithmic scale.

EV = log₂(N² ÷ t) (N: f-number, t: shutter time in seconds)

Combinations with the same EV give the same exposure (for example, stopping down one stop and making the shutter time one stop longer). Multiplying the f-number by √2, or doubling the shutter time, changes the EV by 1.

EV100 is the EV converted to ISO 100. The relation between the EV at an ISO S and EV100 is

EV_S = EV100 + log₂(S ÷ 100), that is, EV100 = EV_S − log₂(S ÷ 100)

At ISO 100, EV = EV100. Doubling the ISO lets the same EV setting handle a scene one stop darker (an EV100 one lower). For example, setting EV 11 at ISO 400 suits a scene with an EV100 of 9.

Three calculations

EV from the settings: finds the EV and EV100 from the f-number, shutter time and ISO.
Find the f-number: from EV100, ISO and shutter time (N = √(t × (ISO ÷ 100) × 2^EV100)).
Find the shutter time: from EV100, ISO and f-number (t = N² ÷ ((ISO ÷ 100) × 2^EV100)).

Precision and "exact values"

Logarithms and powers are calculated with floating-point numbers and then rounded to 12 significant digits. A result is labeled an "exact value" only when the number inside the logarithm (N² ÷ t and so on) is an integer power of two. This is decided with fractions and integers, not from the floating-point result; every other result is a "rounded value". You can choose 0 to 3 decimal places for the EV (the default is 2).

Examples

Input	Result
f/1, 1 second, ISO 100	EV 0 (exact value)
f/4, 1 second, ISO 100	EV 4 (exact value)
f/8, 1/125 second, ISO 100	EV about 12.97 (EV100 is the same)
f/2, 1/60 second, ISO 400	EV about 7.91, EV100 about 5.91

Notes

Nominal f-numbers (2.8, 5.6 and so on) are rounded labels. The tool calculates with the number you type and does not correct it.
EV is not luminance or illuminance (brightness) itself. The tool does not handle the reflectance assumption of a light meter, reciprocity failure, exposure compensation or flash.
The ISO and shutter time ranges are limited (ISO 1 to 1,000,000, shutter time up to 100,000 seconds, EV100 from −30 to 50). Use a period as the decimal separator; commas are accepted only as thousands separators.
For ND filter stops, see the ND Filter Calculator. For shutter angle, see the Shutter Angle Calculator.

Frequently asked questions

What is the difference between EV and EV100?

EV is the value at the ISO you are using. EV100 is the value converted to ISO 100, which describes how bright the scene is regardless of the ISO. At ISO 100 they are the same.

What happens to the EV when I stop down one stop?

Multiplying the f-number by √2 (about 1.414) increases the EV by 1.

Why is the result a "rounded value"?

Logarithms and powers usually do not divide exactly. Only when the number inside the logarithm is an integer power of two is the result shown as an "exact value".