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Color temperature and gel calculator

Convert between kelvin and mireds, preview the color of a light source, and find the CTO or CTB gel that matches your flash to the room.

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About 5500 K. The light you have, for example your flash.
About 3200 K. The light you want to match, for example the room.
Optional. Enter your gel maker's published mired value to get a strength.
Converts any mired value to kelvin.
Mired shift
+131Warming (amber, CTO)
Source
182 mired5,500 K
Target
313 mired3,200 K
Gel suggestion
—Enter your full gel value to get a strength.
Mired to kelvin
5,495 K
Colour of the source and target lightSource 5,500 K and target 3,200 K marked on a strip from about 1500 K (warm) to 10,000 K (cool).Source 5,500 KTarget 3,200 KSource colourTarget colour
Warm light on the left, cool on the right, spaced evenly in mireds. The solid line marks the source and the dashed line the target. Colours are an on-screen approximation.
Common light sources, approximate values
LightApprox. kelvinApprox. mired
Candle flameapprox. 1900approx. 526
Tungsten studio lampapprox. 3200approx. 313
Daylightapprox. 5500–6500approx. 154–182
Open shadeapprox. 7000+approx. 143 or less

How it works

The method behind the numbers.

Kelvin describes how warm or cool a light looks, but equal kelvin steps are not equal colour steps. The mired scale (micro reciprocal degrees) fixes that: a given mired shift looks like about the same colour change anywhere on the scale, which is why gels are rated in mireds.

mired = 10⁶ ÷ K shift = mired(target) − mired(source)
  • A positive shift warms the light (amber, CTO); a negative shift cools it (blue, CTB). The shift is what a filter on the source light, such as a flash, has to add to match the target, such as the room.
  • Gels come in full, half and quarter strengths of CTO and CTB. Their mired values differ by maker and product line, so check your gel maker's published mired value and enter it for a full-strength gel; the tool then suggests the closest strength.
  • Light source figures are approximate and vary with the lamp, the time of day and the sky. Measure with a colour meter or a grey card for critical work.
  • The colour strip uses Tanner Helland's curve fit of blackbody colour ("How to Convert Temperature (K) to RGB", tannerhelland.com, 2012), valid from about 1,000 to 40,000 K. Your display, its settings and the surrounding light change how the colours look, so treat the strip as a preview.
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