Camera Exposure Triangle Calculator

Work the exposure triangle: enter aperture, shutter speed, and ISO to get the EV, or solve for the aperture or shutter that hits a target EV.

Inputs

EV mode reads out the exposure value; the other modes back-solve one setting.

The f-stop, e.g. 2.8 for f/2.8. Used in EV and shutter modes.

Exposure time in seconds. For 1/125 s enter 0.008; for 1/500 s enter 0.002. Used in EV and aperture modes.

Sensor sensitivity. EV is defined at ISO 100; other ISOs shift the metered scene brightness.

Desired exposure value, used when solving for aperture or shutter.

Result

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How to use this calculator

  • Choose what to solve for: EV from your settings, or the aperture/shutter for a target EV.
  • Enter aperture as the f-number (e.g. 2.8) and shutter as seconds (1/125 s = 0.008).
  • Set the ISO; EV is referenced to ISO 100 and the tool shows the ISO shift.
  • In solve modes, set the target EV and read the required setting.

About this calculator

The exposure triangle describes how a photograph's brightness depends on three settings: aperture (the f-number, controlling how much light the lens lets in), shutter speed (how long the sensor is exposed), and ISO (the sensor's sensitivity). They trade off against one another — open the aperture one stop and you can halve the exposure time for the same brightness. This calculator works the triangle two ways. In EV mode it reads out the exposure value of a given aperture and shutter, EV = log₂(N²/t), defined at ISO 100, and shows what scene brightness that exposes correctly at your chosen ISO. In the solve modes it back-calculates the aperture or shutter speed needed to hit a target EV. Each whole number of EV is one "stop" — a doubling or halving of light.

How it works — the formula

EV = log₂(N² ÷ t) (at ISO 100) Aperture: N = √(t × 2^EV_eff) Shutter: t = N² ÷ 2^EV_eff EV_eff = target EV + log₂(ISO ÷ 100)

Exposure value is the base-2 logarithm of the aperture-area-to-time ratio. Solving for one setting inverts the relation; ISO shifts the effective EV the sensor needs by one stop per doubling.

Source: Wikipedia — Exposure value (APEX system)

Worked examples

Example 1
EV: f/2.8, 1/125 s, ISO 100
Inputs:
mode=ev, aperture=2.8, shutter=0.008, iso=100
Output:
log₂(7.84 ÷ 0.008) = EV 9.94
Example 2
EV: f/8, 1/250 s
Inputs:
mode=ev, aperture=8, shutter=0.004
Output:
log₂(64 ÷ 0.004) = EV 13.97
Example 3
Solve aperture: EV 12, 1/500 s, ISO 100
Inputs:
mode=aperture, shutter=0.002, targetEv=12, iso=100
Output:
√(0.002 × 4096) = f/2.9

Limitations

  • EV is defined at ISO 100; the tool shows the ISO shift but EV itself excludes ISO.
  • Ignores lens light-transmission (T-stop vs f-stop) and reciprocity failure.
  • Solved values are exact numbers, not snapped to standard stop increments.

A metering aid; final exposure also depends on metering mode and scene reflectance.

Frequently asked

What is exposure value (EV)?+
EV is a single number that combines aperture and shutter speed: EV = log₂(N²/t), where N is the f-number and t is the shutter time in seconds. It is defined at ISO 100. Each whole EV is one stop — a factor of two in light. Higher EV means less light reaches the sensor (for a brighter scene).
How does ISO fit into the exposure triangle?+
ISO is the sensor's sensitivity. EV itself is defined at ISO 100 and depends only on aperture and shutter. Raising ISO lets the same EV correctly expose a darker scene: doubling ISO (e.g. 100→200) is one stop, equivalent to adding 1 EV of sensitivity. This tool shows that shift.
What is a "stop"?+
A stop is a doubling or halving of light, equal to 1 EV. Going from f/2.8 to f/4 is one stop less light; 1/125 s to 1/250 s is one stop less; ISO 100 to 200 is one stop more sensitivity. You can swap stops between the three settings to keep exposure constant.
How do I enter shutter speed?+
Enter it in seconds. For fractional speeds, divide: 1/125 s = 0.008, 1/500 s = 0.002, 1/1000 s = 0.001. For long exposures enter the whole seconds, e.g. 2 for a 2-second exposure. The output shows the nearest 1/x fraction for readability.
How do I keep the same exposure but freeze motion?+
Use a faster shutter and compensate elsewhere. If you shorten the shutter by one stop (e.g. 1/125→1/250), open the aperture one stop (f/4→f/2.8) or raise ISO one stop (100→200) to keep the same EV at the sensor. Solve mode helps you find the matching setting.
Why is EV defined at ISO 100?+
ISO 100 is the conventional reference sensitivity. Defining EV there makes it a pure function of aperture and shutter, so a given EV always means the same aperture/shutter light regardless of camera. Sensitivity changes are then handled separately as an ISO shift.

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