How to use the colour temperature tool
- Choose the Direction: Kelvin → colour or Colour → temperature.
- For Kelvin to colour, enter the Colour temperature from 1000 K to 40000 K.
- For colour to temperature, set the Colour field to the colour you want to test.
- Read the result, then compare it with the reference strip of light sources from 1500 K to 15000 K.
What it does and when to use it
Photographers, game artists and interface designers often think about light in Kelvin: a warm 2700 K lamp, 5000 K studio light, a 6500 K daylight screen. This tool turns those numbers into colours you can use in CSS, a design tool or a shader, for example to tint a “night mode” overlay or to draw a candle flame.
The reverse direction gives a quick reading of an existing colour. It tells you whether a colour reads as warm, cool or neutral and, for off-whites and creams, roughly what light it resembles. To push a colour warmer by hand, rotate its hue with the HSL adjuster or blend in amber with the colour mixer. For an old-photo warmth, the sepia converter applies the CSS sepia filter.
How it works
Kelvin to colour. The tool uses Tanner Helland’s 2012 approximation, a set of curve fits to blackbody colour data. With T = Kelvin ÷ 100, red is 255 up to T = 66, then falls as a power curve; green follows a logarithm below 66 and a power curve above; blue is 0 below T = 19 and 255 from T = 66.
Colour to Kelvin. The colour is converted to CIE XYZ and then to chromaticity x and y. McCamy’s 1992 formula gives the temperature: n = (x − 0.332) ÷ (0.1858 − y), CCT = 449n³ + 3525n² + 6823.3n + 5520.33. Results outside 1000–40000 K are reported as not meaningful.
Warm or cool is judged by HSL hue: reds to yellows are warm, greens to violets are cool, and very grey, very dark or very light colours are neutral.
Worked examples
These come from the tool itself.
| Input | Result |
|---|---|
| 6500 K | #fffefa, almost white |
| 2700 K | #ffa757, warm orange-white |
| Colour #ffffff | Neutral, 6,505 K |
| Colour #ffd8a8 | Warm, 4,121 K |
| Colour #cadaff | Cool, 10,028 K |
White comes out near 6500 K because sRGB defines its white as the D65 daylight point.
Limits and tips
- The Kelvin colours are an approximation of how light looks, not a colour-managed measurement.
- Very high temperatures change little: 15000 K and 40000 K are both pale blue.
- A “Low” reliability means the colour is far from white light, so its Kelvin value is only nominal.
- It runs in your browser.
Frequently asked questions
What does colour temperature mean?
Why is low Kelvin called warm when it is physically cooler?
Why does converting 2700 K to a colour and back not give 2700 K?
Why does my blue say "Not meaningful"?
Is this accurate enough to match light bulbs?
Sources
- Tanner Helland, How to Convert Temperature (K) to RGB: Algorithm and Sample Code (2012) — tannerhelland.com, accessed 2026-10-08
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