Studio Lighting Ratio Calculator
Calculate studio lighting ratios between key and fill lights.
Find the exposure difference in stops and the resulting contrast on your subject.
A lighting ratio describes the difference in brightness between the key light (main light) and the fill light (shadow-fill light) falling on your subject.
The formula: Lighting Ratio = Key Light Power / Fill Light Power
When expressed in stops, each stop is a doubling or halving of light: Stops = log₂(Ratio) = ln(Ratio) / ln(2)
Common lighting ratios and their effect:
- 1:1: Flat, even lighting. No shadow. Good for high-key beauty shots.
- 2:1: Subtle shadow. Natural, flattering. One stop difference.
- 3:1: Classic portrait ratio. Slight shadow side. Industry standard for headshots.
- 4:1: Two stops. Dramatic but still detailed shadows. Good for character portraits.
- 6:1: Strong drama. Shadow side loses detail. Artistic/moody effect.
- 8:1: Three stops. Very dramatic. Shadow side near black. Fashion/editorial.
How to set a specific ratio: If your key light is at 200 Ws (watt-seconds) and you want a 3:1 ratio, set fill to 200/3 ≈ 67 Ws.
Measuring with a flash meter:
- Meter key light + fill together → this is your “key side” reading
- Meter fill light only → this is your “fill side” reading
- Ratio = 2^(key+fill stops − fill only stops) + 1
Guide number method (speedlights): If using speedlights without a meter, attenuate the fill light using distance (inverse square law) or manual power adjustments. Halving the power = 1 stop reduction.
Recommended ratios by genre:
- Newborn / baby: 2:1: soft and gentle
- Corporate headshot: 3:1: professional, clean
- Beauty / glamour: 2:1 to 3:1
- Dramatic portrait: 4:1 to 6:1
- Film noir style: 8:1 or higher
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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