How does RGB convert to CMYK?

Each RGB channel is normalised to 0-1. The key (black) is one minus the largest channel. Cyan, magenta, and yellow are then derived from the remaining brightness in each channel after removing the black component.

Is this conversion exact for printing?

No. This is the standard arithmetic conversion with no ICC color profile. Real presses use device profiles and ink behaviour, so treat these values as a close starting point rather than a final print spec.

What does the K in CMYK stand for?

K stands for Key, the black plate. Black gets its own ink rather than mixing C, M, and Y because pure black is sharper, cheaper, and avoids the muddy brown that mixed inks produce.

What CMYK does pure black give?

Pure RGB black (0,0,0) converts to 0% C, 0% M, 0% Y, and 100% K. The formula puts all the darkness into the black plate rather than mixing colored inks.

Is anything sent to a server?

No. The conversion runs entirely in your browser using the standard formula. Nothing is uploaded or logged.

RGB to CMYK Color Converter

Convert a screen RGB color into the four-channel CMYK model used for print — Cyan, Magenta, Yellow, and Key (black). Enter the three channels and get the CMYK percentages instantly with a matching swatch.

How it works

RGB is an additive model (light), while CMYK is subtractive (ink absorbing light). The standard conversion normalises each channel to 0–1, pulls out the darkest part as the black plate, then derives the colored inks:

r' = R/255   g' = G/255   b' = B/255
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 the color is pure black (K = 1), the divisions are undefined, so C, M, and Y are all set to 0. Each result is multiplied by 100 to give a percentage.

Example

Convert rgb(59, 130, 246):

r′ = 0.231, g′ = 0.510, b′ = 0.965
K = 1 − 0.965 = 0.035 → 4% K
C = (1 − 0.231 − 0.035) / 0.965 ≈ 76% C
M = (1 − 0.510 − 0.035) / 0.965 ≈ 47% M
Y = (1 − 0.965 − 0.035) / 0.965 ≈ 0% Y

Notes

This is a profile-free conversion, so it is a strong starting point but not a substitute for a color-managed workflow with an ICC profile. The whole calculation runs in your browser — nothing is uploaded.