Portrait Lighting Ratio Calculator
Reviewed by Hamza Gujjar, Algorithm Architect & Software Developer
Last updated: July 27, 2026Portrait Lighting Ratio Calculator
Want consistent, repeatable portrait lighting? This calculator converts key and fill light meter readings into a standard lighting ratio.
Stops Difference = 2 x log2(Key Light f-stop / Fill Light f-stop)
Ratio = 2^(Stops Difference)
Example
Key light meters at f/11, fill light meters at f/5.6:
Stops Difference = 1.9 → 3.9:1 lighting ratio
Reading the Ratio
A 2:1 ratio produces soft, low-contrast lighting flattering for most beauty and commercial portrait work, while ratios of 8:1 or higher create dramatic, high-contrast lighting associated with classic "Rembrandt-style" dramatic portraiture.
Why Measuring in Stops Rather Than Raw f-Numbers
Each full stop represents a doubling of light, so converting the f-stop difference into stops (rather than comparing raw f-numbers directly) correctly reflects the actual perceived contrast difference between the two light sources.