About the Exposure Value Calculator
This exposure value (EV) calculator turns an aperture and shutter speed into a single exposure number, adjusts it for ISO, and then finds equivalent settings that give exactly the same exposure. Enter a working combination — for example from your camera meter or a test shot — then choose the aperture and ISO you would rather use, and it returns the shutter speed you need, both exactly and rounded to the nearest standard 1/3-stop setting.
It is handy for switching to a wider aperture for background blur, stopping down for depth of field, adding an ND filter or flash, or working with a hand-held light meter. The table lists every full-stop aperture from f/1.4 to f/22 with the matching shutter speed, so you can see the trade-off between motion blur and depth of field at a glance.
EV here follows the standard APEX definition, EV = log₂(N² ÷ t). The light level is also expressed as EV at ISO 100 (EV₁₀₀), which describes the scene itself and is matched to typical lighting conditions such as full sun (about EV 15) or an evening interior (about EV 5). Shutter values use the nominal markings you see on cameras.
With the default inputs, the exposure value (ev) of these settings is 12.97. Change any value above to recalculate instantly.
How to use the exposure value calculator
- 1Enter an aperture, shutter speed and ISO that give a correct exposure (from your meter or a test shot).
- 2Read the EV and the typical lighting it corresponds to.
- 3Enter the aperture you would like to use instead.
- 4Change the ISO too if you want to trade noise for speed.
- 5Use the equivalent shutter speed, or pick another row from the table.
Formula and method
Exposure value combines aperture and shutter speed into one number: every +1 EV halves the light reaching the sensor. Because light through the lens scales with the square of the f-number, opening up by one full stop (f/8 to f/5.6) lets you halve the exposure time for the same result. EV₁₀₀ subtracts the ISO effect so the number describes the brightness of the scene itself.
To keep exposure identical, the new shutter time is scaled by the square of the f-number ratio and inversely by the ISO ratio. The illuminance estimate uses the incident-light meter equation with calibration constant C = 250, giving lux ≈ 2.5 × 2^EV₁₀₀. Nominal camera markings (f/5.6, 1/125) are rounded from exact powers of two, so results can differ by a few percent from the marked values.
- N
- Aperture f-number
- t
- Shutter time in seconds
- EV
- Exposure value at the shooting ISO
- EV₁₀₀
- Exposure value normalised to ISO 100 (scene brightness)
Worked examples
f/8 at 1/125 s, ISO 100 → open up to f/4
EV = log₂(8² ÷ (1/125)) = log₂(8000) ≈ 12.97, a bright overcast scene. Opening from f/8 to f/4 admits 2 stops more light, so the shutter must be 4× faster: 1/125 ÷ 4 = 1/500 s.
Sunny 16 at ISO 200, switching to f/2.8 for blur
The sunny 16 rule gives f/16 at 1/200 s for ISO 200, which is EV 15.64 (about EV 14.6 at ISO 100). Moving to f/2.8 needs (2.8/16)² = 0.0306 times the exposure — about 1/6,530 s, so the nearest setting is 1/6400 s.
Indoor: f/2.8, 1/30 s, ISO 1600 → f/4 at ISO 3200
The EV of f/2.8 at 1/30 s is log₂(7.84 × 30) ≈ 7.88, or about EV 3.9 at ISO 100 — a dim room of roughly 37 lux. Stopping down to f/4 costs about one stop, which doubling the ISO to 3200 cancels, so the shutter works out to 1/29.4 s and the nearest setting is still 1/30 s.
Frequently asked questions
What is exposure value (EV)?+
EV is a single number for a combination of aperture and shutter speed: EV = log₂(N²/t). Every combination with the same EV lets in the same amount of light, so f/8 at 1/125 s and f/5.6 at 1/250 s are both about EV 13.
Is a higher EV brighter or darker?+
A higher EV setting lets in less light, so it is used for brighter scenes. Full sun is around EV 15 at ISO 100, while a typical living room at night is around EV 5.
How does ISO change EV?+
Doubling ISO lets you use settings one EV higher for the same scene. The calculator shows both the EV of your settings and EV at ISO 100, which describes the scene brightness independent of ISO.
What is the sunny 16 rule?+
In bright sun, set the aperture to f/16 and the shutter speed to roughly 1 ÷ ISO — for example 1/100 s at ISO 100. That corresponds to about EV 15 at ISO 100.
Why does my camera show 1/125 instead of 1/128?+
Camera markings are rounded for readability. Exact full stops would be 1/128, 1/256 and so on, and f-numbers are rounded powers of √2 (f/5.6 is really f/5.657), so calculated values can differ slightly from the dial.
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