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Exposure Calculator

PhotographyExposure and Camera Settings

The number after f/, e.g. 2.8, 5.6 or 16.

Shutter speed entered as
Exposure value at ISO 100 (EV100) —
EV of aperture and shutter alone
—
ISO offset from 100 (stops)
—
Light level these settings suit
—
Where the EV100 sits from night to sun on snow
The chart appears with your result

Exposure value is EV = log2(N² ÷ t), where N is the f-number and t the shutter time (s). To compare across ISO, subtract log2(ISO ÷ 100). For example, f/16 at 1/125 s and ISO 100 gives log2(32,000) = 14.97, so EV 15, the reading for bright sun.

About this tool

Photographers use exposure values to compare settings that let in the same light: f/8 at 1/250 s and f/5.6 at 1/500 s are both close to EV 14. This calculator takes the aperture, the shutter speed (as a fraction like 1/125 or in whole seconds for long exposures) and the ISO, and returns the EV referenced to ISO 100, the number printed in light-meter tables and lens charts. It also shows the EV of aperture and shutter alone, how many stops your ISO sits above or below 100, and a rough description of the scene brightness the settings would expose correctly, drawn on a scale from night to sun on snow. It treats marked f-numbers and shutter speeds as exact, so a camera's nominal f/5.6 (really f/5.66) and 1/125 s (really 1/128 s) can shift the result by a few hundredths of a stop.

How to use it

  1. Enter the aperture

    Type the f-number from the lens or camera display, such as 2.8 or 11.

  2. Choose how to enter the shutter

    Pick Fraction for speeds like 1/250 s and type 250, or Whole seconds for long exposures such as 4 s.

  3. Set the ISO

    Enter the sensor or film sensitivity; 100 leaves the EV unchanged.

  4. Read EV100 and the scene

    The headline is the ISO 100 exposure value; the scale and scene line tell you what lighting it matches.

Examples

f/16, 1/125 s, ISO 100

Aperture (f-number)
16
Shutter speed entered as
Fraction (1/x s)
Shutter speed 1/
125
ISO
100

Result Exposure value at ISO 100 (EV100): 15.0
EV of aperture and shutter alone: 15
ISO offset from 100 (stops): 0
Light level these settings suit: Bright sun on ordinary subjects

  1. Shutter time t = 1/125 s = 0.008 s
  2. EV = log2(N² ÷ t) = log2(256 ÷ 0.008) = 14.97
  3. ISO offset = log2(100 ÷ 100) = 0 stops
  4. EV100 = 14.97 − 0 = 14.97

The sunny 16 rule in numbers: 256 ÷ (1/125) is 32,000, and log2 of that is 14.97, which reads as EV 15, the textbook value for full sun.

f/2.8, 1/60 s, ISO 1600

Aperture (f-number)
2.8
Shutter speed entered as
Fraction (1/x s)
Shutter speed 1/
60
ISO
1600

Result Exposure value at ISO 100 (EV100): 4.9
EV of aperture and shutter alone: 8.9
ISO offset from 100 (stops): 4
Light level these settings suit: Typical home or office interior

  1. Shutter time t = 1/60 s = 0.016667 s
  2. EV = log2(N² ÷ t) = log2(7.84 ÷ 0.016667) = 8.88
  3. ISO offset = log2(1600 ÷ 100) = 4 stops
  4. EV100 = 8.88 − 4 = 4.88

The aperture and shutter give EV 8.9, but ISO 1600 is four stops above 100, so the scene they expose correctly is about EV100 4.9, a lamp-lit room.

How it is calculated

EV = log2(N² ÷ t); EV100 = EV − log2(ISO ÷ 100)

N
f-number of the aperture
t
shutter time, s
ISO
arithmetic ISO speed
EV100
exposure value referenced to ISO 100

The APEX system defines EV 0 as f/1 for one second. Each full stop of aperture multiplies N² by 2 and each halving of shutter time doubles 1/t, so every step adds 1 EV. Raising the ISO lets the same settings work in dimmer light, so the light level they suit drops by log2(ISO ÷ 100) stops. That ISO 100 value is what meter tables list for scenes: about EV 15 for direct sun and 5 to 7 for home interiors.

When not to use it

  • It does not meter a scene; use a light meter or the camera reading for the actual brightness.
  • For flash exposure the shutter barely matters, so EV here says little about the flash result.
  • Cine lenses marked in T-stops transmit less light than the f-number implies, so the EV differs slightly.

Common mistakes

  • Typing 125 in Whole seconds mode when the shutter is 1/125 s, which is off by about 14 stops.
  • Forgetting that a higher ISO lowers EV100, not raises it.
  • Comparing an EV at ISO 400 with a table written for ISO 100 without the 2-stop offset.

Frequently asked questions

Why does a higher EV mean less light reaches the sensor?

EV counts how bright a scene must be for the settings to expose it. A small aperture and fast shutter, such as f/16 at 1/1000 s, admit very little light, so they only suit a bright scene and carry a high EV. Wide apertures and long shutter times give low or negative EVs suited to dark scenes.

What is the difference between EV and EV100?

EV comes from aperture and shutter alone. EV100 adjusts it for ISO so it describes scene brightness on the scale light-meter tables use. At ISO 100 the two are equal; at ISO 400 EV100 is 2 lower than EV.

Which settings give the same exposure as f/8 at 1/250 s?

Any pair with the same EV, about 14. Open one stop to f/5.6 and halve the time to 1/500 s, or close to f/11 and lengthen to 1/125 s. Enter each pair here and the EV stays within a few hundredths, the gap coming from the rounded markings on cameras.

What EV is typical for common scenes?

Published meter tables give roughly EV100 15 to 16 for sunlit subjects, 16 or more for sun on snow or sand, 12 to 13 for overcast days, 5 to 7 for home interiors and about 2 or less for streets at night. Treat them as starting points; real scenes vary by a stop or two.

Can the exposure value be negative?

Yes. Long exposures with wide apertures, such as f/2 for 30 seconds at ISO 100, give about EV −2.9. Negative values are normal for moonlit landscapes, astrophotography and very dark interiors.

Does the result change for film versus digital?

No. The formula uses the ISO speed only, which film boxes and camera settings express on the same arithmetic scale. Reciprocity failure in film during very long exposures is a separate correction this calculator does not apply.

Cite this tool

Using this tool in an assignment, article or report? Copy a citation, or a link for your website.

APA

Tools Directory Editorial Team. (2026, October 16). Exposure Calculator. Tools Directory. Retrieved October 27, 2026, from https://tools.milunir.com/photography/exposure-and-camera-settings/exposure-calculator/

MLA

Tools Directory Editorial Team. “Exposure Calculator.” Tools Directory, 16 Oct. 2026, https://tools.milunir.com/photography/exposure-and-camera-settings/exposure-calculator/. Accessed 27 Oct. 2026.

Chicago

Tools Directory Editorial Team. “Exposure Calculator.” Tools Directory. Last modified October 16, 2026. Accessed October 27, 2026. https://tools.milunir.com/photography/exposure-and-camera-settings/exposure-calculator/.

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