Exposure value calculator

Exposure value turns the two settings that control how much light reaches the sensor, aperture and shutter time, into a single number. Photographers use it to think in stops, to swap one setting for another without changing the picture's brightness, and to compare scenes. This calculator gives the EV of a setting, the equivalent pairs, the difference between two settings in stops, the effect of a neutral density (ND) filter, and the Sunny 16 starting point.

How exposure value is defined

The camera standard Exif (CIPA DC-008, Annex C) builds on the APEX system, in which every quantity is a logarithm in base 2. The aperture value is Av = 2 × log2(N), the time value is Tv = −log2(t), and the exposure value is their sum: Ev = Av + Tv = log2(N² ÷ t). The same Annex ties it to the scene and the film speed with Ev = Bv + Sv, where the speed value Sv = log2(ISO ÷ 3.125). Because Sv is 5 at ISO 100 and rises by one with each doubling of ISO, the value for any ISO can be moved to the ISO 100 scale: EV100 = EV − log2(ISO ÷ 100). That is the number to quote when you describe how bright a scene is.

The table samples Table 52 of the Exif standard, whose aperture and time columns are separate lists rather than pairs. It lists the full-stop f-numbers 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22 and 32, and times from 30 seconds to 1/2000. The numbers on lenses and cameras are rounded: f/5.6 stands for 5.657, f/11 for 11.31 and f/22 for 22.63, and 1/60 s is really 1/64. The calculator reads the typed 1.4, 2.8, 5.6, 11 and 22 as the exact values they stand for, so f/8 to f/5.6 comes out as exactly one stop.

Worked example

You meter a scene at f/8, 1/125 s, ISO 100. N² = 64 and 64 ÷ 0.008 = 8,000, so EV = log2(8,000) = 12.97, which is EV100 12.97 because the ISO is 100. Equivalent settings keep the product N² ÷ t, so opening up one stop to f/5.6 allows half the time, 1/250 s, and f/4 allows 1/500 s; closing down to f/11 needs 1/62 s, which you would set as 1/60. Switch to ISO 400 and the same scene is EV 14.97 at that ISO (two stops more), still EV100 12.97. The shift of two stops is why 1/500 s at ISO 400 and 1/125 s at ISO 100 expose alike.

Neutral density filters

Edmund Optics gives the relation as transmission T = 10^(−OD) and OD = −log(T), and adds that stacked filters add their densities. A stop is a factor of 2, so stops = OD × log2(10) = OD × 3.32. A filter with OD 0.3 is almost exactly one stop (1.995×), OD 0.9 is 2.99 stops (about 3, the filter often written ND8), and OD 3.0 is 9.97 stops. The exposure time grows by the filter factor: 1/125 s with a 1000-fold filter is 8 s. Filters are labeled in different ways, with a factor such as 8 or 1000, a number of stops, or a density such as 0.9 or 3.0, which is why the calculator accepts all three: enter what your filter's marking says.

Sunny 16 and typical daylight

Kodak's TRI-X data sheet prints a daylight exposure table for average front-lit subjects from two hours after sunrise to two hours before sunset. For ISO 400 film at 1/500 s it lists f/22, f/16, f/11, f/8 and f/5.6 for light that ranges from bright sun on light sand or snow down to heavy overcast or open shade. Each step is one stop. Worked out as EV100 those are 16.0, 15.0, 14.0, 13.0, 12.0, close to 16, 15, 14, 13 and 12. The popular Sunny 16 rule is the second line of that table with the shutter set to about 1/ISO: at ISO 100, f/16 at 1/125 s.

Limits of these numbers

EV describes the setting, not the scene. It is a good guide only when the metering matches the subject: a snow field and a black cat in the same light need different settings, and the table above assumes an average front-lit subject. The Sunny 16 line is a rule of thumb from film days; check the picture and adjust, and the rule fails at dawn, dusk and in shade. Film also loses sensitivity in long exposures: Kodak's sheet for TRI-X says an indicated 1 second needs 2, 10 seconds needs 50 and 100 seconds needs 1,200 (about +1, +2 and +3 stops). So an ND-filter time from this page is a starting point for film. We could not read ISO 2720, the exposure-meter standard, because it is sold rather than published; the definitions here come from the Exif standard and the manufacturers' documents named below.

Common mistakes

Typing the shutter as 125 when you mean 1/125 (the box reads a plain number as seconds). Forgetting that the f-number is squared: one stop is a factor of 1.41 in the f-number, not 2. Comparing EV values taken at different ISO without moving them to EV100. And mixing up "EV" the scene or setting number with "EV" in exposure compensation, where +1 EV just means one stop brighter than the meter's choice.

What is exposure value (EV)?

Exposure value is one number that stands for a combination of aperture and shutter time. It is defined as EV = log2(N² ÷ t), where N is the f-number and t is the exposure time in seconds. EV 0 is f/1 at 1 second, and every step of 1 is one stop, a doubling or halving of the light. Different settings with the same EV give the same exposure at the same ISO, so f/8 at 1/125 s (EV 12.97), f/5.6 at 1/250 s and f/4 at 1/500 s are equivalent.

How do I calculate EV from aperture and shutter speed?

Square the f-number, divide by the exposure time in seconds and take the base-2 logarithm. For f/8 at 1/125 s: 8² = 64, 64 ÷ (1/125) = 8,000, and log2(8,000) = 12.97. The camera standard Exif writes this as Ev = Av + Tv, with the aperture value Av = 2 × log2(N) and the time value Tv = −log2(t): here Av = 6 and Tv = 6.97. Marked camera speeds are rounded, so 1/125 s is not exactly the 1/128 s that would give a whole EV 13.

What is EV100 and how does ISO change EV?

EV100 is the exposure value expressed for ISO 100, so scenes and settings can be compared whatever ISO the camera is set to: EV100 = EV − log2(ISO ÷ 100). Doubling the ISO is one stop, so ISO 400 shifts the value by 2. A camera set to f/16 at 1/500 s and ISO 400 has EV 16.97, which is EV100 14.97, the same as f/16 at 1/125 s and ISO 100. The Exif standard writes the relation as Ev = Bv + Sv, with the speed value Sv = log2(ISO ÷ 3.125), which is 5 at ISO 100.

How many stops apart are two exposures?

The picture's brightness rises with shutter time and ISO and falls with the square of the f-number, so the difference in stops is the difference of the two EV100 values. Going from f/8 to f/5.6 at the same shutter time and ISO is 1.00 stop of extra light. Going from f/8, 1/125 s, ISO 100 to f/8, 1/250 s, ISO 400 is 1.00 stop: half the shutter time costs a stop and the ISO gains two. Use the compare mode for any pair.

How do ND filter numbers, stops and density relate?

A neutral density filter's optical density OD is the base-10 logarithm of how many times it dims the light: transmission T = 10^(−OD), the factor is 1 ÷ T, and the stops are log2 of the factor, which is OD × 3.32. So a density 0.9 filter is 7.94× (2.99 stops, which is the filter often written ND8: 8×, 3 stops), and a density 3.0 filter is 1,000×, which is 9.97 stops, close to 10 stops (exactly 10 stops would be 1,024×). Stacked filters add their densities and stops and multiply their factors: densities 0.3 and 1.5 make 1.80, which transmits 1.58% (Edmund Optics). With a 1000-fold filter, 1/125 s becomes 8 s.

What is the Sunny 16 rule?

A rule of thumb, not a law: on a bright sunny day with distinct shadows, set the aperture to f/16 and the shutter time to about 1 over the ISO. At ISO 100 that is f/16 at 1/125 s (the nearest full-stop speed to 1/100), which has an EV100 of 15.0. Kodak's data sheet for TRI-X 400 film gives the same arrangement at 1/500 s: f/22 for bright sun on light sand or snow, f/16 for bright or hazy sun with distinct shadows, f/11 for weak hazy sun with soft shadows, f/8 for cloudy bright with no shadows, and f/5.6 for heavy overcast or open shade, for average front-lit subjects from two hours after sunrise to two hours before sunset.

What EV do different kinds of light have?

Kodak's daylight table, expressed at ISO 100, works out to about 16, 15, 14, 13, 12 for its five conditions in order, from bright sun on sand or snow down to heavy overcast or open shade (our arithmetic from Kodak's f-numbers at 1/500 s and ISO 400, not a figure Kodak prints). Indoors and at night the values fall below that, and we have no source we could read for them, so the calculator does not list them. A camera's light meter is the right tool for those.

For the optics behind a setting, use the depth of field calculator and the field of view calculator; to size the prints from the picture, the PPI calculator and the print size calculator.

Sources, read October 27, 2026: Camera & Imaging Products Association, CIPA DC-008-2012, Exif Version 2.3, Annex C (APEX units) and Table 52; Kodak Alaris, KODAK PROFESSIONAL TRI-X 320 and 400 Films, F-4017 (October 2021), Exposure section; Edmund Optics, Understanding Neutral Density Filters. How we check our calculators.