Camera Exposure Calculator
Exposure value, or EV, packs aperture and shutter speed into one number so photographers can reason about light in stops. This calculator computes EV from the three pillars of the exposure triangle: the aperture f-number, the shutter time in seconds, and the ISO. It uses the standard APEX exposure relationship, where each whole EV is one stop, a doubling or halving of light. Enter your settings and it returns the base-ISO-100 EV, the EV at your chosen ISO, and the equivalent number of stops of ISO gain so you can balance the exposure triangle.
Exposure value formula
EV (ISO 100) = log2( aperture^2 / shutter time )
ISO gain (stops) = log2( ISO / 100 )
EV (at chosen ISO) = EV (ISO 100) + ISO gain
(one EV step = one stop = factor of 2 in light)
This is the standard APEX exposure relationship. The aperture squared over shutter time captures the optical exposure, and the base-two logarithm turns the light ratio into stops. ISO shifts the working point by its own base-two logarithm relative to ISO 100.
Photography context
- One stop is a doubling or halving of light, equal to one EV.
- The exposure triangle trades aperture, shutter speed, and ISO against one another for the same exposure.
- EV 15 is roughly bright sunlight; EV 0 is a one-second exposure at f/1.0 at ISO 100.
- Doubling ISO adds one stop of effective exposure but can increase image noise.
- The APEX system underlies the EV scale used on light meters and in camera firmware.
Camera exposure: frequently asked questions
What is exposure value (EV)?
Exposure value is a single number that combines aperture and shutter speed to describe how much light reaches the sensor or film. Each whole step of EV represents a doubling or halving of light, one stop. It lets photographers compare and trade off aperture and shutter settings on one scale.
What is the exposure value formula?
At base ISO 100, EV equals the base-two logarithm of the aperture (f-number) squared divided by the shutter time in seconds. ISO adjusts this: EV at the chosen ISO is the base-100 EV plus the base-two logarithm of ISO divided by 100. This is the standard APEX exposure relationship.
What does one stop mean?
One stop is a doubling or halving of the light reaching the sensor, a change of one EV. Opening the aperture by one stop, halving the shutter time, or doubling the ISO each add one stop of exposure. Photographers think in stops because the eye responds to light roughly logarithmically.
How does ISO affect exposure value here?
Raising ISO makes the sensor more sensitive, so a given scene needs less light for the same brightness. In this calculator, doubling the ISO from 100 adds one to the EV figure at that ISO, reflecting one extra stop of effective exposure. The aperture and shutter define the optical EV; ISO shifts the working point.
Is a higher EV brighter or darker?
A higher EV corresponds to a brighter scene or more restrictive camera settings, meaning a smaller aperture or faster shutter is needed. EV 15 is roughly bright daylight, while EV 0 corresponds to a one-second exposure at f/1.0. Each EV step is one stop, a factor of two in light.
Official sources
- International Organization for Standardization: ISO 12232 photographic exposure.
- NIST: SI units, the second.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.