Exposure Value (EV) Calculator
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Exposure value (EV) from aperture, shutter speed, and ISO — the APEX exposure formula.
Exposure settings
Enter shutter speed in seconds, e.g. 0.008 for 1/125s.
Exposure value (EV)
12.97
f/8 · 1/125s · ISO 100
- Shutter speed
- 1/125s
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Exposure value (EV)
Exposure value (EV) is a single number that summarizes how much light reaches the sensor for a given aperture, shutter speed, and ISO combination, using the APEX system: EV = log₂(N² / t) − log₂(ISO / 100), where N is the f-number and t is the shutter speed in seconds.
Many different aperture/shutter/ISO combinations can produce the same EV and therefore the same overall exposure — this is the basis of the "exposure triangle." Each full stop change in any one setting shifts EV by exactly 1.
Example: the classic "Sunny 16" rule (f/16, 1/125s, ISO 100) works out to EV ≈ 14.97, a typical value for bright daylight. Opening up to f/8 at the same shutter speed and ISO drops EV to about 12.97 — 2 stops brighter, since f/16 to f/8 is a 2-stop change in aperture.
Common questions
Why would I calculate EV instead of just using my camera's meter?
EV is useful for comparing exposures across cameras or lighting conditions, cross-checking a light meter reading, or working with EV-based flash and studio lighting guides.
Does doubling my shutter speed change EV by exactly 1?
Yes — halving the shutter time (a full stop faster) increases EV by 1, and doubling it (a full stop slower) decreases EV by 1, all else being equal.