Exposure Triangle Calculator

Exposure Value (EV) is photography's standard unit for describing how much light a scene has, independent of which specific camera settings you use to capture it. This calculator computes EV100 — exposure value at the ISO 100 reference sensitivity — using the standard formula EV = log2(N² / t), where N is your f-number (aperture) and t is your shutter time in seconds (1 divided by the shutter speed denominator you entered, so "250" becomes 1/250s). It then adjusts that figure for your actual ISO with evAtIso = EV100 − log2(ISO/100), since raising ISO effectively lowers the light needed for the same exposure, which subtracts from the EV100 reading. The brightness assessment is a lookup table against the EV100 value: EV100 of 15+ maps to bright sunlight, 13+ to overcast daylight, down through golden hour, indoor lighting, and finally very dark/night sky below EV 0 — giving you an intuitive sense of what lighting condition your settings imply.

Motion blur risk is a separate lookup keyed only to shutter speed denominator (500+ freezes fast action, 125+ freezes normal motion, down to below 15 requiring a tripod for long exposures), independent of aperture or ISO. The three equivalent exposures demonstrate the core reciprocity concept of the exposure triangle: any of several ISO/aperture/shutter combinations can produce the identical EV, because doubling one setting's light contribution while halving another's cancels out. Equivalent 1 doubles both ISO and shutter speed (denominator) together; Equivalent 2 opens the aperture by one stop (dividing the f-number by √2 ≈ 1.414) while doubling shutter speed; Equivalent 3 closes aperture by one stop (multiplying by √2) while halving shutter speed. Note this stops at the shutter speed floor of 1 (can't go below 1/1s in equiv 3's math), and none of these equivalents account for diffraction softness at very small apertures or noise at very high ISOs — the EV math treats all three variables as freely interchangeable, but real image quality is not indifferent to which one you push.