Photography Exposure Calculator
Exposure value from aperture, shutter speed, and ISO, with the light level named.
What it does
Every exposure is a trade among three dials: how wide the lens opens, how long the shutter stays open, and how much the sensor amplifies what little light arrives. The exposure value, EV, compresses the aperture and shutter pair into a single number, and EV100 tells you how much light is actually there.
The tool above takes an aperture, a shutter time, and an ISO. It returns the EV of the setting itself, the light level as EV100, and a plain language name for that light, from bright daylight down to candlelit.
The default setting is the classic Sunny 16 rule: f/16, 1/125 s, ISO 100 reads 15.0 EV, bright daylight. Drop to f/11 and the same light reads 13.9 EV; open up to f/2.8 at ISO 800 under shade and the dial reads 5.9 EV.
The math follows the ISO 2720 exposure value definition and a NASA exposure reference: EV equals log base 2 of the aperture squared divided by the shutter time, with ISO folded in as a log base 2 of the speed ratio.
How to use
- Enter the aperture as an f-number, like 8 or 2.8.
- Enter the shutter time as a fraction or decimal seconds.
- Enter the ISO you plan to shoot.
- Press Calculate for EV100 and the light level name.
- Change one dial and watch how EV moves in stops.
Formula
- N
- Aperture as an f-number, the focal length divided by the entrance pupil.
- t
- Shutter time in seconds; 1/125 s enters as 0.008.
- EV
- Exposure value of the aperture and shutter pair at any ISO.
- ISO
- Sensor speed; doubling ISO adds one stop and lifts EV100 by one.
Each whole EV step is one stop: doubling the light halves EV. EV100 is the useful one for comparing scenes because it strips out your chosen ISO; the ISO 2720 standard defines the arithmetic, and the NASA reference tabulates typical scene values from starlight to bright sun.
Worked example
Example: sunny 16 and two variations
Defaults: f/16, shutter 1/125, ISO 100.
- Aperture squared: 16 x 16 = 256.
- Divide by shutter: 256 / 0.008 = 32,000.
- EV = log2(32000) = 14.97, shown as 15.0 EV.
- ISO 100 adds no shift, so EV100 is also 15.0, bright daylight.
- At f/11, 121 / 0.008 = 15,125, so EV100 is 13.9.
- At f/2.8, 1/60 s, ISO 800: EV 8.88 minus 3 stops of ISO gives 5.9 EV, indoor light.
Reference table
| Scene | EV100 | Sunny 16 setting |
|---|---|---|
| Bright daylight | about 15 | f/16 at 1/125 s |
| Bright daytime, slightly overcast | about 13 | f/16 at 1/500 s |
| Cloudy or open shade | about 12 | f/8 at 1/500 s |
| Indoor bright, stage lit | about 9 | f/4 at 1/125 s |
| Typical indoor, gym | 6 to 7 | f/2 at 1/60 s |
| Twilight, candlelight | 1 to 3 | tripod needed |
Limits
- Names the light; does not meter it.
- Film reciprocity effects are ignored.
- Diffraction and motion blur are not judged.
- EV assumes a standard lens transmission.
Common mistakes
- Reading EV100 as the setting EV when ISO is not 100.
- Typing 1/125 with spaces or letters.
- Thinking a higher EV means a brighter photo; it means brighter light.
- Forgetting ISO shifts EV by whole stops.
- Treating the bands as exact; scenes vary.
Try it yourself
Quick checks. Answers sit tucked under each question.
f/8, 1/250 s, ISO 100?
EV = 13.0, bright daytime; 64 / 0.004 = 16,000.
f/4, 1/60 s, ISO 400?
EV 8.9, EV100 about 6.9 with the two stop ISO shift.
Same light, f/8 at 1/125 vs f/5.6 at 1/250?
Equal EV: one stop wider over one stop faster keeps the exposure.
Questions
What is EV?
A single number for an aperture and shutter pair; equal EV means equal light energy on the sensor for a given scene brightness.
Why logs with base 2?
Photography counts in stops, and one stop is a doubling, which is exactly what log base 2 measures.
How does ISO enter?
Raising ISO from 100 to 800 is three doublings, so EV100 drops three from the setting EV.
What is Sunny 16?
On a sunny day set f/16 and a shutter near 1/ISO seconds; ISO 100 lands near 1/125 s, which reads about 15 EV.
Can I get the same exposure many ways?
Yes; all settings along one EV line look equally bright, differing only in depth of field, motion blur, and noise.
Is EV the same across cameras?
By definition yes, though tiny lens transmission differences add a fraction of a stop in practice.