RGB to CMYK Converter
Convert screen RGB colors to CMYK ink percentages for print — cyan, magenta, yellow and key (black) from any 0–255 color.
How it works
K = 1 − max(R',G',B') · C = (1−R'−K)/(1−K) · M = (1−G'−K)/(1−K) · Y = (1−B'−K)/(1−K), where R'=R/255
RGB is additive light on a screen; CMYK is subtractive ink on paper, so the conversion first pulls out the shared darkness as the K (key/black) channel, then expresses the remaining color as cyan, magenta and yellow. Pure black (0,0,0) becomes K = 100% with no CMY. This is a device-independent approximation — real presses use ICC profiles because inks, paper and press conditions shift the exact mix, so treat these percentages as a starting point, not a proof.
Worked example
RGB(52, 152, 219): R'=0.204, G'=0.596, B'=0.859. K = 1 − 0.859 = 0.141. C = (1 − 0.204 − 0.141)/0.859 = 0.76, M = (1 − 0.596 − 0.141)/0.859 = 0.31, Y = (1 − 0.859 − 0.141)/0.859 = 0.00 — about 76% cyan, 31% magenta, 0% yellow, 14% black.
Frequently asked questions
Why does my printed color look different from the screen?
Screens emit light and cover a wider gamut than ink absorbs, so vivid blues, greens and neon tones simply cannot be reproduced in CMYK. A precise match needs an ICC color profile for your specific printer and paper.
What is the K channel for?
K stands for "key" — the black plate. Mixing cyan, magenta and yellow to make black wastes ink and looks muddy, so presses add a dedicated black to deepen shadows and sharpen text.
Is this conversion exact?
It is the standard math conversion, but true print color depends on the press profile. Use it to get close, then soft-proof with your printer’s ICC profile before a final run.
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