Lighting Ratio Calculator
Calculate source and combined lighting ratios from incident light measurements.
Use incident metering. This calculator uses the additive fill convention; lighting-ratio definitions vary, so both ratios are shown.
Results
- Source ratio K/F
- Combined lit-side ratio (K+F)/F
- Stops log2((K+F)/F)
References: Rangefinder Online, “Understanding Light Ratios: Additive and Source Methods”; Photo Nova, “Ratios.”
Calculated locally in your browser.
A QUICK WALKTHROUGH
How to use this tool
- Enter K and F in the same incident-light unit, with K ≥ 0 and F > 0.
- Calculate and review the formula scope.
- Use incident metering. This calculator uses the additive fill convention; lighting-ratio definitions vary, so both ratios are shown.
Formula and scope
Use incident metering. This calculator uses the additive fill convention; lighting-ratio definitions vary, so both ratios are shown.
Source
References: Rangefinder Online, “Understanding Light Ratios: Additive and Source Methods”; Photo Nova, “Ratios.”
Local processing
Calculated locally in your browser.
GOOD TO KNOW
Common questions
Why are two ratios shown?
K/F compares source contributions; (K+F)/F compares the combined lit side with the fill baseline. Definitions vary.