Lighting Ratio Calculator

About this calculator

In photographic and cinematic lighting, the lighting ratio compares how much brighter the key light is than the fill light, expressed in stops — each stop is a doubling of light, so the ratio is calculated as stops = log₂(key light level ÷ fill light level). A 1-stop difference is a 2:1 ratio (mild, flattering contrast), 2 stops is 4:1 (classic dramatic portrait look), and 3+ stops pushes into deep, moody chiaroscuro territory.

Portrait and studio photographers use this to dial in consistent, repeatable looks across a shoot, while cinematographers and gaffers use the same stop math when setting up key-to-fill contrast for a scene's mood, matching it to the story's tone or a director's shot list.