White Balance Calculator — Kelvin & Mired Conversion

Mired (micro reciprocal degree) is calculated as 1,000,000 / Kelvin. The advantage of mired over Kelvin is that equal mired shifts produce equal perceived colour changes regardless of the starting temperature. A shift of 50 mired always looks the same, whereas a shift of 500K looks very different at 2000K vs 8000K.

Direct midday sunlight is approximately 5200K. Overcast sky is around 6000-6500K (bluer). Open shade under blue sky can be 7500-10000K. Flash units are typically calibrated to 5500K. Golden hour light drops to around 3500-4000K.

CTO (Colour Temperature Orange) filters warm light by adding positive mired shift. CTB (Colour Temperature Blue) filters cool light by adding negative mired shift. A full CTO gel is about +159 mired (LEE 204, converting 6500K daylight to 3200K tungsten) up to +167 mired (Rosco 3407, converting 5500K to roughly 2900K). Converting flash (5500K) to tungsten (3200K) is a shift of about +131 mired — between a 3/4 and a full CTO. These gels are used on flash units and studio lights to match ambient colour temperature.

If shooting RAW, white balance can be changed in post-processing with no quality loss — it is simply metadata. However, setting it correctly in-camera gives you accurate preview images and histograms. If shooting JPEG, white balance is baked in and should be set accurately before shooting.