RGB to CMYK converter

The RGB to CMYK formula

1. Divide R, G and B by 255 to get R′, G′, B′ between 0 and 1.
2. K = 1 − max(R′, G′, B′).
3. C = (1 − R′ − K) ÷ (1 − K), M = (1 − G′ − K) ÷ (1 − K), Y = (1 − B′ − K) ÷ (1 − K).
4. Multiply by 100 for percentages. If K = 1 (black), C, M and Y are 0.

Worked example

rgb(230, 120, 40) → R′ .902, G′ .471, B′ .157
K = 1 − .902 = .098 → 10%
C = 0%, M = 48%, Y = 83%
Result: cmyk(0%, 48%, 83%, 10%)

Good to know

• This is the device-independent formula. A print shop converts with an ICC profile for their press and paper (FOGRA39 in Europe, GRACoL/SWOP in North America), which gives different — and more accurate — numbers.
• Bright screen colours like rgb(0, 255, 0) are outside what CMYK inks can reproduce; they will print duller.
• For rich black on press, designers often use something like C60 M40 Y40 K100 rather than K100 alone.

Need the colour from an image first? Use the colour picker from image — it shows all formats at once.