How to use it
- Type the Aperture as an f-number, such as 16, and the Shutter time (seconds) as a decimal, such as 0.008 for 1/125 second.
- Type the ISO of your settings.
- Read the Exposure value (EV) at this ISO and the EV at ISO 100.
- Use the Equivalent exposures table to find another aperture with the shutter time that gives the same EV.
How the exposure value is calculated
The Exposure value article on Wikipedia defines EV as the base-2 logarithm of the f-number squared divided by the exposure time in seconds. EV 0 is one second at f/1.0, and each increase of 1 EV is one stop: twice the light, or half of it when the value falls.
At an ISO S, the settings give EV_S, and the EV at ISO 100 is EV_100 = EV_S − log2(S / 100). A sensitivity of ISO 800 is three stops above ISO 100. So at ISO 800 the same settings suit a scene three EV darker, and the same scene needs settings three EV higher.
EV = log2(N² ÷ t)
EV at ISO 100 = EV − log2(ISO ÷ 100)
Equivalent time for another aperture: t = N² ÷ 2^EVTypical lighting, as EV at ISO 100
The article's Table 2 gives the EV at ISO 100 of common lighting. Its values are taken from the ANSI exposure guides PH2.7-1973 and PH2.7-1986, which the article says are guidelines to be used with caution; a range shows where the two guides differ. Side lighting lowers the EV by 1 and back lighting by 2, as the article's footnote states.
| Lighting | EV at ISO 100 |
|---|---|
| Light sand or snow in full or slightly hazy sunlight | 16 |
| Typical scene in full or slightly hazy sunlight | 15 |
| Typical scene in hazy sunlight (soft shadows) | 14 |
| Typical scene, cloudy bright (no shadows) | 13 |
| Typical scene, heavy overcast; areas in open shade in clear sunlight | 12 |
| Just after sunset | 9 to 11 |
| Neon and other bright signs | 9 to 10 |
| Night sports | 9 |
| Bright street scenes | 8 |
| Offices and work areas | 7 to 8 |
| Home interiors | 5 to 7 |
What the calculator does not cover
- Which exposure makes a particular picture: EV describes the amount of light for a set of settings and does not choose the aperture or time for you.
- The lighting table: it is a guide from the article's sources, not a measurement of your scene.
Worked example: f/16 at 1/125 second, ISO 100
The exposure value is log2(16² ÷ 0.008) = log2(32,000) = 14.97. The Exposure value article uses this exact case, 1/125 second at f/16, to show EV 15 with a single number.
The same product of N² and time, 32,000, gives the same EV at ISO 100: f/8 at 1/500 second and f/4 at 1/2000 second. A wider aperture needs a shorter time.
| Settings at ISO 100 | EV at ISO 100 |
|---|---|
| f/16, 1/125 second | 14.97 (EV 15) |
| f/8, 1/500 second | 14.97 |
| f/4, 1/2000 second | 14.97 |
Frequently asked questions
What is an exposure value?
An exposure value (EV) is one number that combines the aperture and the shutter time into a measure of how much light the sensor receives. The Exposure value article on Wikipedia defines it as the base-2 logarithm of N squared divided by the time.
Why is EV 0 at f/1.0 and one second?
The article states that EV 0 corresponds to an exposure time of 1 s and an aperture of f/1.0, and that each increase of 1 in EV is one stop of exposure, twice or half the light.
What is the difference between EV and EV at ISO 100?
EV describes the settings at the ISO you used. EV at ISO 100 removes the ISO by subtracting log2 of the ISO divided by 100, so settings made at different ISO values can be compared.
What are equivalent exposures?
Equivalent exposures are combinations of aperture and time that give the same EV at the same ISO. Opening the aperture by one stop halves the time, so the table lists each aperture with the time that keeps the EV the same.
Are the lighting values exact?
No. The article gives them from the ANSI exposure guides PH2.7 and says they are guidelines to be used with caution. Ranges show where the guides differ, so treat them as a starting point for your own metering.
Does the EV tell me the right settings for a photo?
No. An exposure value measures the light for a set of settings. It does not choose the aperture or the time for a picture, which depends on the depth, the motion and the look you want.
Sources
Figures and text last checked on Tuesday, November 10, 2026.