Tools / Color Converter / RGB → CMYK

RGB to CMYK Converter.

RGB to CMYK converts a screen color (additive light) into the four subtractive ink channels a printer uses. This is a screen-approximation: true print color depends on paper, ink, and an ICC profile, so always confirm with a proof. The math here gives the standard 'naive' CMYK most tools display.

Enter a RGB color

CMYK —

All formats

The RGB → CMYK formula

Normalize to 0-1. K = 1 − max(R,G,B). C = (1−R−K)/(1−K), M = (1−G−K)/(1−K), Y = (1−B−K)/(1−K). If K = 1 (pure black), C=M=Y=0.

Worked example

Convert rgb(27, 42, 78):

Normalize → (0.106, 0.165, 0.306)
K = 1 − 0.306 = 0.694 → 69%
C = (1−0.106−0.694)/0.306 ≈ 65%
M ≈ 46%, Y = 0%
Result: cmyk(65%, 46%, 0%, 69%)

JavaScript

function rgbToCmyk(r,g,b){
  r/=255;g/=255;b/=255;
  const k=1-Math.max(r,g,b);
  if(k===1) return [0,0,0,100];
  return [(1-r-k)/(1-k),(1-g-k)/(1-k),(1-b-k)/(1-k),k].map(v=>Math.round(v*100));
}

FAQ

Will print match my screen?

Not exactly. RGB has a wider gamut than CMYK, so vivid blues and greens shift. This formula is a preview; for production, soft-proof with the printer's ICC profile.

Why is there a K (black) channel?

Mixing C+M+Y to make black wastes ink and looks muddy, so printers add a dedicated key (black) plate. K absorbs the common darkness first.

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Library

Colour references for your next project

Compare the original references behind this archive. Check the contents, edition and format before choosing a book.

Book links are Amazon Associates affiliate links. Your price is unchanged; a small commission supports the archive. As an Amazon Associate we earn from qualifying purchases.

Sanzo Wada

A Dictionary of Color Combinations

The 2010 Seigensha republication of the 1933 original. Japanese import.

Every combination in it is already browsable free here, hex values and all. Buy this one for the object rather than the data — Seigensha's matte plates and Japanese binding, or a citable copy of the 1933 original. If you want plates this archive doesn't have, Vol. 2 is the one.

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Sanzo Wada

A Dictionary of Color Combinations Vol. 2

Seigensha, 2020. Japanese import.

Wada's 1935–1938 follow-ups: 72 plates on the Japanese seasons and 165 drawn from early-century fashion, interior, and graphic design. Not in Vol. 1. Not in this archive. The book itself is a design object — Japanese binding, matte pages, zero captions.

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Torn between the two Wada dictionaries? Vol 1 vs Vol 2, compared plate by plate →