Exposure value (EV) reduces the whole exposure triangle to a single number, making it easy to compare scene brightness and swap between equivalent camera settings. This calculator computes EV from any aperture, shutter, and ISO, then lists every aperture and shutter pair that produces the same exposure.
How it works
Exposure value is defined from aperture and shutter speed:
EV = log₂(N² ÷ t)
where N is the f-number and t is the shutter time in seconds. Each whole step
of EV equals one stop of light. Because light meters reference ISO 100, the tool
normalizes to EV100:
EV₁₀₀ = EV − log₂(ISO ÷ 100)
Raising ISO makes the sensor more sensitive, so the same brightness corresponds to a higher EV — the normalization lets you compare scenes regardless of ISO.
Equivalent exposures
Two settings are equivalent when they let the same total light reach the sensor.
Opening the aperture one stop doubles the light, and shortening the shutter one
stop halves it, so the two cancel. The tool holds N² ÷ t constant and solves for
the shutter time at each standard aperture:
t = N² ÷ 2^EV
Worked example
A meter reading of f/8 at 1/250 s and ISO 100 gives:
EV = log₂(8² × 250) = log₂(64 × 250) = log₂(16,000) ≈ 13.97 — essentially EV 14.
The equivalent exposure at f/2.8 would solve to approximately 1/2000 s. Brightness is identical, but you have gained:
- A shallower depth of field from the wider aperture
- Frozen motion from the faster shutter
Or, if you wanted to slow the shutter to blur water at f/22, the equivalent would be roughly 1/15 s — four stops slower than 1/250 s, matching the four-stop aperture change from f/8 to f/22.
Common EV reference values
| Scene | Typical EV100 |
|---|---|
| Direct sunlight (Sunny 16) | 15 |
| Lightly overcast | 13–14 |
| Open shade | 12 |
| Bright interior | 7–9 |
| Candlelit room | 4–5 |
| Night street scene | 3–5 |
These reference values help you cross-check whether your meter reading is plausible for the light around you.
When to use equivalent exposures
The most common scenario is depth of field control: you want a specific aperture for creative reasons (wide open for a blurred background, stopped down for sharp landscapes) but the meter suggests a different aperture. Use the equivalent list to find the shutter speed that compensates, keeping the same EV.
A second scenario is motion rendering: a sports shot may need 1/1000 s minimum to freeze action. If your current EV means 1/1000 s requires f/2, but your lens only goes to f/2.8, you need to raise ISO — increasing EV at the sensor level — until 1/1000 s becomes achievable at f/2.8. EV normalization makes this arithmetic immediate.
The EV system also makes light-meter readings portable across camera systems, since a spot reading in EV means the same thing on any camera, regardless of manufacturer.