Exposure Value Calculator
Exposure value (EV) is a single number that encodes a camera exposure setting, combining aperture (f-number) and shutter speed into one quantity. Defined by the APEX (Additive System of Photographic Exposure) standard, EV 0 corresponds to an aperture of f/1 at a shutter speed of 1 second. Each increase of 1 EV represents a halving of the light reaching the sensor (one stop). The EV100 figure calculated here is independent of ISO: it measures the light in the scene itself at the ISO 100 reference. The ISO-adjusted EV shows how your chosen ISO changes the effective exposure. Knowing the EV of a scene lets you understand scene brightness in absolute terms, compare different shooting situations, and quickly find equivalent exposure combinations that all produce the same result. This calculator also generates a table of equivalent exposures at f/8 across four common ISOs, so you can see at a glance how changing ISO trades off against shutter speed. The scene description is derived from the standard EV reference table published by photographic standards bodies and widely reproduced in photographic education. Enter your aperture, shutter speed and ISO to see your EV instantly.
EV at ISO 100: -- | Scene: --
Equivalent exposures at f/8
Any combination of aperture, shutter speed and ISO that produces the same EV will give the same exposure on the sensor. The table below shows what shutter speed you would need at f/8 to match your current EV100, across four common ISOs.
| ISO | Aperture | Shutter speed (to match your EV) |
|---|---|---|
| Enter values above to see equivalent exposures. | ||
How EV is calculated
The exposure value formula comes from the APEX system, where each camera parameter is expressed on a base-2 logarithmic scale. EV100 depends only on aperture and shutter speed, and represents the scene brightness at the ISO 100 reference.
EV100 = log2(N² / t)
EV_ISO = EV100 + log2(ISO / 100)
Where N is the f-number and t is the shutter speed in seconds. The log2 function converts multiplicative stops into an additive scale.
Worked example
Aperture f/5.6, shutter speed 1/100 s (0.01 s), ISO 400:
- N² = 5.6² = 31.36
- N² / t = 31.36 / 0.01 = 3,136
- EV100 = log2(3136) = 11.61 (approximately 12, typical of a bright overcast day)
- log2(ISO / 100) = log2(400 / 100) = log2(4) = 2
- EV_ISO = 11.61 + 2 = 13.61
EV reference: scene brightness guide
The following EV100 values correspond to typical lighting conditions. These figures are derived from the standard EV reference table used in photographic education and are referenced in the APEX system documentation and photographic standards.
| EV100 (approx.) | Lighting condition |
|---|---|
| 16 | Bright beach or snow in direct sun |
| 15 | Bright direct sunlight (sunny 16 reference) |
| 14 | Slightly hazy sun |
| 12 | Overcast bright (soft shadows) |
| 10 | Overcast (no shadows) |
| 8 | Open shade or heavily overcast |
| 7 | Indoor bright (window light) |
| 5 | Indoor dim (away from windows) |
| 3 | Twilight after sunset |
| 0 | Full moon lit scene |
| −3 | Quarter moon lit scene |
The sunny 16 rule and EV
The sunny 16 rule states that in bright direct sunlight, you should set your aperture to f/16 and your shutter speed to 1/ISO seconds. For example, at ISO 100, use 1/100 s; at ISO 200, use 1/200 s. This corresponds to an EV100 of approximately 15, which is the standard reference for direct sunlight. The rule is a useful sanity check when a light meter is unavailable, and it is consistent with the EV scale: EV100 = log2(16² / (1/100)) = log2(25,600) = approximately 14.6, rounded to EV 15.
The EV scale lets photographers compare, communicate and record shooting conditions in a compact, unambiguous form. Flash guide numbers, lighting ratios and exposure compensation are all expressed in terms of EV stops, making the EV system the common language of photographic exposure.
Exposure value calculator: frequently asked questions
What is exposure value (EV)?
Exposure value (EV) is a single number that combines aperture (f-number) and shutter speed into one measure of camera exposure. An EV of 0 is defined as f/1 at 1 second. Each increase of 1 EV halves the amount of light reaching the sensor (one stop). EV100 refers to EV calculated at ISO 100, which is commonly used as a scene-brightness reference independent of ISO setting.
What EV is correct for daylight photography?
Bright, direct sunlight on a clear day typically produces an EV100 of around 15. This is the basis of the sunny 16 rule: at f/16 and ISO 100, the correct shutter speed is approximately 1/100 s (or 1/125 s on common shutter speed scales). Overcast conditions drop to around EV 10 to 12, and deep shade or twilight can fall as low as EV 3 to 5.
How does ISO affect EV?
ISO sensitivity does not change the physical exposure value of a scene, but it changes how the camera captures that scene. The ISO-adjusted EV shifts the reference: each doubling of ISO adds 1 EV of effective sensitivity. So shooting at EV100 of 12 with ISO 400 is equivalent in terms of sensor capture to shooting at EV100 of 14 at ISO 100, because ISO 400 is 2 stops more sensitive than ISO 100.
What is the sunny 16 rule?
The sunny 16 rule is a practical exposure guide: in bright sunlight, set your aperture to f/16 and use a shutter speed approximately equal to 1/ISO (for example, ISO 100 gives 1/100 s, ISO 200 gives 1/200 s). This produces a correct exposure without a light meter. The rule corresponds to EV100 of approximately 15 and has been the standard reference for outdoor photography for decades.
How are EVs used in practice?
EVs appear in camera metering systems, light meters, and exposure guides. A light meter measures scene luminance and returns an EV, which the camera (or photographer) then translates into an aperture and shutter speed combination. EV tables published by manufacturers and standards bodies (such as ISO 2720) list recommended EVs for specific lighting conditions, from bright sunlight down to starlight. Flash guide numbers are also linked to EV concepts.
Official sources
- Wikipedia: Exposure value (APEX system and EV tables).
- Cambridge in Colour: Understanding Camera Exposure.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology. General information only.