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.