Exposure Value Calculator
Computes the Exposure Value (EV) from your aperture and shutter speed, giving a single number that represents the total light entering the camera. Use it to compare exposure settings or match lighting conditions across different scenes.
About this calculator
Exposure Value (EV) is a base-2 logarithmic scale that combines aperture and shutter speed into a single dimensionless number representing the amount of light reaching the sensor. The formula is EV = log₂(N² / t), where N is the aperture f-number and t is the shutter speed in seconds. EV 0 is defined as f/1 at 1 second. Each increase of 1 EV represents half as much light (one stop). At ISO 100, EV 15 corresponds to bright sunlight, while EV 0 corresponds to very low light. EV is useful for understanding exposure equivalence — multiple combinations of aperture and shutter speed can yield the same EV, giving photographers flexibility to prioritize depth of field or motion blur.
How to use
Suppose you shoot at f/8 and a shutter speed of 1/125 s (0.008 s). Apply the formula: EV = log₂(8² / 0.008) = log₂(64 / 0.008) = log₂(8,000). Since log₂(8,000) = ln(8,000) / ln(2) ≈ 8.987 / 0.693 ≈ 12.97, your EV is approximately 13. EV 13 at ISO 100 corresponds to a slightly overcast bright day. You could achieve the same exposure at f/5.6 and 1/250 s, or f/11 and 1/60 s, all giving EV ≈ 13.
Frequently asked questions
What does Exposure Value (EV) mean in photography?
EV is a standardized number that describes the total luminous exposure of a camera setting independent of ISO. It combines aperture and shutter speed into one figure so photographers can quickly compare or communicate lighting conditions. An EV difference of 1 always represents a factor of 2 in exposure — exactly one stop. Because EV is logarithmic, adding 1 EV halves the exposure time needed for the same result, making it a compact way to describe a very wide range of lighting situations.
How do aperture and shutter speed combine to determine EV?
In the EV formula, the aperture f-number is squared before being divided by the shutter speed in seconds. Squaring the aperture is necessary because the area of the lens opening — and therefore the light admitted — scales with the square of the diameter, which is inversely proportional to the f-number. Shutter speed appears in the denominator, so a faster shutter speed (smaller t) raises EV, meaning less light. Both controls have equal weight per stop: opening the aperture one stop or doubling the shutter speed both change EV by exactly 1.
How is EV related to ISO and correct exposure?
The EV scale as calculated from aperture and shutter speed is calibrated to ISO 100. To find the 'correct' EV for a scene at a different ISO, you add log₂(ISO/100) to the scene's luminance EV. For example, shooting at ISO 400 (two stops above ISO 100) effectively increases your camera's sensitivity by 2 EV, allowing you to use settings two stops darker. Light meters and in-camera metering systems use this relationship to recommend aperture-shutter combinations that match the measured scene EV at the selected ISO.