Exposure Value Calculator

Enter an aperture, shutter speed and ISO to find the exposure value (EV), then see equivalent settings that give the same exposure — faster shutter, wider aperture or a different ISO. A table of typical scene EVs helps you estimate exposure without a meter.

What exposure value means

Exposure value (EV) is a single number that describes combinations of aperture and shutter speed that let in the same amount of light. It was introduced so that photographers could lock exposure and shift between settings without changing the result. Formally, EV = log₂(N² ÷ t), where N is the f-number and t the shutter time in seconds. f/1 at 1 second is EV 0; f/8 at 1/125 is about EV 13. Every increase of 1 EV means half as much light reaches the sensor — one stop less exposure.

EV and ISO

The same formula can describe scene brightness when it is tied to a sensitivity. Light meters and charts usually quote EV at ISO 100: the settings that correctly expose a scene at ISO 100. If you raise ISO, you need less light, so the camera settings give a higher EV for the same scene: at ISO 400 you can use settings two EV higher (two stops less light) than at ISO 100. The calculator reports both the EV of your settings and the equivalent scene brightness at ISO 100.

Typical scene EV values (ISO 100)

The “Sunny 16” rule follows from this: in bright sun, set f/16 and a shutter speed close to 1/ISO. At ISO 100 that is f/16 at 1/100 or 1/125 — about EV 15.

Equivalent exposures

Because EV counts stops, you can trade shutter speed for aperture one stop at a time without changing exposure: f/8 at 1/125, f/5.6 at 1/250 and f/11 at 1/60 are all EV 13. Use this to choose what matters for the photo — a fast shutter to freeze motion, a wide aperture for background blur, or a small aperture for depth of field — while keeping the brightness the same. The calculator lists equivalents across the full-stop aperture scale.

Worked example

Your meter suggests f/8 at 1/125 at ISO 100 on an overcast day: EV 12.97, about EV 13. You want a blurred background for a portrait, so you open to f/2.8 — three stops wider. To keep the same exposure you shorten the shutter three stops to 1/1000. If you later move to ISO 400 indoors where the scene is EV 7 at ISO 100, the settings at ISO 400 correspond to EV 9 — for example f/2.8 at 1/60.

Stops, thirds and camera dials

Modern cameras usually adjust in third-stop increments: 1/125, 1/160, 1/200, 1/250, and f/5.6, f/6.3, f/7.1, f/8. The calculator works with any value, so you can enter third-stop settings to see fractional EVs. Remember that f-numbers change by a factor of about 1.4 (the square root of 2) per stop because the light gathered depends on the area of the aperture.

Using EV in practice

• Exposure compensation is expressed in EV: +1 EV brightens by one stop, −1 EV darkens by one stop.
• Bracketing takes shots at, for example, −1, 0 and +1 EV for HDR or safety.
• Neutral density filters are rated in stops (ND8 = 3 stops): subtract that from the scene EV to find long-exposure settings.
• Flash and lighting ratios are often discussed in stops of difference between light sources.

EV and light meter readings

Handheld light meters often display EV directly, and many camera specifications quote their metering range and autofocus sensitivity in EV — for example, autofocus “down to −4 EV” means the system can still focus in extremely dim light equivalent to a moonlit scene. Reading EV lets you compare equipment and conditions across different aperture and shutter combinations. When a meter reports EV 12 at ISO 100, you can pick any pair from the equivalents list for that value, and adjust by one EV for every doubling or halving of ISO.

Metering modes and tricky scenes

A camera meter aims to render whatever it measures as a mid-tone. That works for average scenes but misleads in extremes: snow and white sand come out grey unless you add +1 to +2 EV of compensation, and a dark subject against a black background can be overexposed unless you subtract. Spot metering reads a small area, letting you meter a face or a mid-tone deliberately; centre-weighted and matrix (evaluative) modes average larger areas. Checking the histogram after a test shot is the quickest way to confirm the exposure value you chose was right.