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