Aperture Calculator: EV, F-Stop and Exposure Value
Exposure value (EV) is a single number that summarises how much light a camera setting combination lets through to the sensor. It is calculated from two of the three exposure triangle controls: aperture (f-stop) and shutter speed. A third control, ISO, adjusts how sensitive the sensor is to that light, and this calculator accounts for all three. The formula is EV = log2(N^2 / t), where N is the aperture f-number and t is the shutter speed in seconds. The resulting EV is referenced to ISO 100 by convention; at ISO 200 you effectively gain one stop of sensitivity, so the ISO-adjusted EV rises by log2(ISO / 100). Knowing a scene's EV helps you choose settings: bright sunlight is typically EV 15, an overcast day around EV 12, and a typical indoor room around EV 7. Each whole number change in EV represents a halving or doubling of light. A higher f-stop number (such as f/16) gives a smaller aperture opening and a higher EV for a given shutter speed, meaning the lens is letting in less light than at f/2.8. Select your f-stop, shutter speed and ISO below to see the exact EV and an approximate scene description.
EV at ISO 100: -- | EV adjusted for ISO: --
How EV is calculated
The exposure value formula combines aperture and shutter speed into one quantity. It was standardised in ISO 2720:1974 and is used in camera metering systems worldwide.
EV = log2(N^2 / t)
EV_ISO = EV + log2(ISO / 100)
Where N is the aperture f-number and t is the shutter speed in seconds. The ISO adjustment adds stops of effective sensitivity on top.
Worked example
Settings: f/4, 1/125 s (0.008 s), ISO 400:
- N^2 = 4^2 = 16
- N^2 / t = 16 / 0.008 = 2,000
- EV = log2(2000) = 10.97 (approximately 11.0 at ISO 100)
- ISO gain = log2(400 / 100) = log2(4) = 2.00 stops
- EV adjusted = 10.97 + 2.00 = 12.97 (approximately overcast daylight)
EV reference: common scenes at ISO 100
| Scene | Typical EV (ISO 100) |
|---|---|
| Bright sunlight on snow or sand | 16 |
| Full sunlight | 15 |
| Slightly overcast | 13 to 14 |
| Overcast or open shade | 11 to 12 |
| Heavily overcast | 10 |
| Indoor bright office lighting | 7 to 8 |
| Indoor home lighting | 5 to 6 |
| Candlelit interior | 3 to 4 |
| Night: well-lit street | 1 to 3 |
| Night: moonlit landscape | -2 to 0 |
Source: Cambridge in Colour, Understanding Camera Exposure. Values are approximate and vary with conditions.
Aperture, shutter speed and ISO: the exposure triangle
Every exposure is a balance between three controls. Aperture (f-stop) controls depth of field as well as light. A wide aperture (low f-number) blurs the background and lets in lots of light. A narrow aperture (high f-number) gives a deep, sharp field of view but requires more light or a slower shutter speed.
Shutter speed controls motion: fast shutter speeds freeze action while slow speeds blur motion. ISO amplifies the sensor signal: higher ISO values allow shooting in low light but introduce noise (grain). The skill of exposure is balancing all three to get a correctly lit image with the depth of field and motion rendering you want.
EV is a convenient shorthand: once you know a scene's EV, you can choose any combination of f-stop and shutter speed that gives the same EV, and let the artistic needs (depth of field, motion) guide which combination you pick.
Aperture calculator: frequently asked questions
What is exposure value (EV)?
Exposure value (EV) is a single number that combines aperture (f-stop) and shutter speed into one quantity representing the amount of light reaching the sensor. EV 0 corresponds to f/1.0 and a 1-second exposure at ISO 100. Each whole EV step doubles or halves the light. It is defined as EV = log2(N^2 / t), where N is the f-number and t is the shutter speed in seconds. EV is commonly used in photographic light meters and scene-luminance tables.
How does aperture affect exposure?
Aperture controls how wide the lens iris opens. A wider aperture (lower f-number, such as f/1.4) lets in more light, while a narrower aperture (higher f-number, such as f/16) lets in less. Each full f-stop change doubles or halves the light reaching the sensor. For example, changing from f/2.8 to f/4 is one stop less light, requiring you to double your shutter speed or raise ISO to maintain the same exposure.
What is a stop in photography?
A stop is a unit of measurement for light in photography. One stop represents a doubling or halving of the amount of light. In aperture, moving one stop wider (e.g. f/8 to f/5.6) doubles the light. In shutter speed, doubling the time (e.g. 1/250 s to 1/125 s) is one stop more light. In ISO, doubling the value (e.g. ISO 400 to ISO 800) is one stop more sensitivity. The exposure triangle (aperture, shutter speed, ISO) is all about balancing these stops.
What are common EV values for everyday scenes?
Typical EV values at ISO 100 are approximate guides: Bright sunlight (EV 15), Lightly overcast (EV 12 to 13), Heavy overcast or open shade (EV 11 to 12), Indoor office lighting (EV 7 to 8), Indoor home lighting (EV 5 to 6), Candlelit scene (EV 3 to 4), Night street with lights (EV 1 to 3), Night without artificial lighting (EV -2 to 0). These are starting points; actual brightness varies with season, latitude and subject reflectance.
How does ISO affect exposure value?
The standard EV formula assumes ISO 100. When you use a higher ISO, your sensor becomes more sensitive and can achieve the same apparent exposure with less light. The ISO-adjusted EV is: EV_ISO = EV100 + log2(ISO / 100). For example, at ISO 400 you gain 2 stops of effective sensitivity, so an EV 12 scene can be shot at the same settings as an EV 14 scene at ISO 100. This calculator shows both EV at ISO 100 and EV adjusted for your chosen ISO.
Official sources
- Cambridge in Colour, Camera Exposure tutorial: Understanding Camera Exposure.
- Wikipedia, Exposure value: Exposure value (ISO 2720:1974).
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology. General information only.