CCT Kelvin to Mireds Calculator

CCT in kelvin and mireds

The mired (micro reciprocal degree) is a color-temperature unit defined as M = 10⁶ / K. What makes it handy is that mired shifts come out linear and perceptually uniform. Subtract mireds and you move toward warmer light (lower K) by the same visual amount every time, whereas equal kelvin steps feel wildly different at 3000 K compared to 8000 K. A few reference points: daylight is 6500 K = 154 mired, tungsten 3200 K = 312 mired, and a candle sits around 1850 K ≈ 540 mired. The classic CTO (Color Temperature Orange) gel adds roughly +167 mired, enough to drag 5600 K down to about 3200 K; a CTB (Color Temperature Blue) pulls the other way (~−131 mired) to take tungsten up to daylight. You'll also find half and quarter strength versions, like 1/4 CTO ≈ +42 mired.

Applications

Picking gel filters for cinema and photo work (Rosco/Lee CTO/CTB). Fine-tuning white balance in DSLR/mirrorless menus, where the steps are mired-equivalent. The Temp slider in Lightroom/Camera Raw, which works in mired under the hood. Matching mixed sources, say a tungsten lamp against a window full of daylight. And theatrical lighting design, where you need small linear shifts to behave predictably.

FAQ

Why use mireds instead of kelvin directly? A +100 K shift at 3000 K is huge to the eye, but +100 K at 9000 K you can barely see. Mireds keep filter math additive, so stacking two +42 mired gels lands you at exactly +84 mired.

How do I convert a kelvin shift to a mired shift? Work out M1 = 10⁶/K1 and M2 = 10⁂/K2, then take ΔM = M2 − M1. A positive ΔM points warmer, the CTO direction; a negative one points cooler, the CTB direction.

Are mireds the same as "decamireds"? No. A decamired equals 10 mireds and shows up on some older Kodak Wratten filter charts. Today's gel manufacturers spec their products in plain mireds.