RGB to CMYK Converter

From light to ink: what actually changes

RGB and CMYK answer opposite questions. A monitor starts black and adds red, green and blue light; a printed page starts white and subtracts light with cyan, magenta, yellow and black inks. Cyan is the opposite of red, magenta of green, yellow of blue — which is why the conversion mostly consists of flipping each channel and pulling out a shared black component.

The standard formula, step by step

First normalize each RGB channel to the range 0–1 by dividing by 255. Then:

K  = 1 − max(R′, G′, B′)
C  = (1 − R′ − K) ÷ (1 − K)
M  = (1 − G′ − K) ÷ (1 − K)
Y  = (1 − B′ − K) ÷ (1 − K)

Take rgb(53, 100, 196). Normalized: R′ = 0.208, G′ = 0.392, B′ = 0.769. The largest channel is B′, so K = 1 − 0.769 = 0.231. Then C = (1 − 0.208 − 0.231) ÷ 0.769 = 0.730, M = (1 − 0.392 − 0.231) ÷ 0.769 = 0.490, and Y = (1 − 0.769 − 0.231) ÷ 0.769 = 0. Rounded to percentages: cmyk(73%, 49%, 0%, 23%) — a blue built mostly from cyan with some magenta, no yellow, and a fifth of black.

The honest part: real printing uses ICC profiles

The formula above is the standard device-independent approximation that every online converter (including this one) uses. Real prepress conversion is different: it runs through an ICC profile that describes a specific combination of press, ink and paper — European coated stock (FOGRA), US web offset (GRACoL/SWOP), newsprint, and so on. The same RGB color can legitimately become different CMYK numbers under different profiles, because each press has its own gamut and dot gain.

Practical consequences: use these values for orientation, quick specs and rough matching — but let your print shop (or your layout software with the shop’s profile) do the final conversion. Two more prepress details worth knowing:

• Total ink limit. Presses cap the sum C+M+Y+K (often 280–320%). A naive conversion never exceeds 300% by construction for any single color, but designed rich blacks can.
• Rich black vs 100K black. Body text prints as plain 0/0/0/100 (crisp, no registration issues); large dark areas often use a “rich black” like 60/40/40/100 for depth. A naive RGB→CMYK conversion of #000000 gives plain 100K — fine for text, thin for posters.

Why your print looks duller than your screen

The CMYK gamut is smaller than sRGB: no ink combination reproduces a glowing screen cyan or a saturated RGB green. Converters quietly pull such colors to the nearest printable neighbor, which is why proofs look muted next to monitors. Judge print colors under print conditions — on paper, in daylight — not by comparing a proof to a backlit display.

Everything here runs locally in your browser; the values you convert are never uploaded. For the reverse direction use the CMYK to RGB converter, and to fine-tune a color before converting, the universal color converter shows every notation at once.