Work out exposure value, shutter speed, aperture or ISO
This exposure value calculator solves the one equation behind every exposure. Enter any three of the four things that matter, a scene brightness (EV100), an aperture, a shutter speed and an ISO, and it finds the fourth. It also lists equivalent exposures, so you can see which shutter speed goes with each aperture without changing the picture’s brightness.
It is useful as a pen-and-paper light meter, for planning night or astrophotography exposures, and for checking the Sunny 16 rule. Everything is computed in your browser.
How to use the exposure calculator
- Choose what to find: exposure value, shutter speed, aperture or ISO. That field becomes read-only and shows the answer.
- Pick a scene brightness from the preset list, or type your own EV100 from a light meter.
- Enter the other settings. Shutter speeds can be typed as 1/125, 0.5 or 30 seconds.
- Read the result, the nearest standard setting and the table of equivalent exposures. Press Sunny 16 preset for the daylight starting point.
Exposure Value Calculator features
Four ways round
Solve for EV, shutter speed, aperture or ISO with the same inputs.
Equivalent exposures
Ten apertures from f/1.4 to f/32 with the matching shutter speed, exact and rounded to a standard value.
Scene EV100 table
Typical values from bright snow (16) to the Milky Way (about −10).
The exposure value formula
Exposure value is defined as EV = log₂(N² ÷ t), where N is the f-number and t the shutter time in seconds. It comes from the exposure equation N² ÷ t = L × S ÷ K prescribed by ISO 2720, in which L is the scene luminance, S the ISO speed and K a calibration constant, 12.5 cd/m² per ISO second. Every step of 1 EV is one stop: half or double the light.
Because ISO changes how much light the camera needs, brightness is quoted at ISO 100: EV100 = EV − log₂(ISO ÷ 100). To get a shutter speed, the calculator uses t = N² ÷ (2^EV100 × ISO ÷ 100). At f/8, ISO 100 and EV100 15 that is 64 ÷ 32,768 = 1/512 s. Luminance follows as 0.125 × 2^EV100 cd/m², so EV100 15 is about 4,096 cd/m².
Sunny 16 and typical scene values
The Sunny 16 rule says that in bright sun with distinct shadows, f/16 and a shutter speed of 1 ÷ ISO give a good exposure. In numbers, f/16 at 1/100 s and ISO 100 is EV 14.6, which rounds to the table value of 15. Take one stop off for hazy sun, two for bright cloud, and so on down the list in the preset menu. The values come from the typical scene table on Wikipedia’s “Exposure value” page, which cites the ANSI exposure guides PH2.7-1973 and PH2.7-1986. They are rounded guidelines, not measurements.
Limits
The result assumes a correct middle-grey exposure. Backlit, very bright or very dark scenes need exposure compensation, and the lux figure assumes an incident-meter constant of 250, which varies by maker. Very long exposures also suffer reciprocity failure on film and extra noise on sensors, so treat anything past a few minutes as a starting point.
Exposure Value Calculator FAQ
How do I calculate exposure time?
Pick the scene’s EV100, the aperture and the ISO, then t = N² ÷ (2^EV100 × ISO ÷ 100). Choose “Shutter speed” in the Find box and the calculator does it.
What is EV100?
The brightness of a scene expressed as the exposure value at ISO 100. Sunny daylight is about 15, an overcast day 12, a home interior 5 to 7.
What is the Sunny 16 rule?
In full sun, use f/16 and a shutter speed of 1 ÷ ISO, for example 1/100 s at ISO 100.
Are f/8 at 1/250 s and f/5.6 at 1/500 s the same exposure?
Yes, they give the same EV. Opening the aperture one stop lets you halve the exposure time. Depth of field and motion blur differ.
Does ISO change the exposure value?
The EV of the settings depends only on aperture and shutter. ISO changes the scene EV100 that those settings suit: each doubling of ISO suits a scene one stop darker.
Can I use this for ND filters or astrophotography?
Yes for the base exposure. Use the ND filter calculator to add a filter, and the star trail calculator for 500 rule and NPF limits.