RGB to CMYK Color Converter
Convert RGB color values to CMYK (cyan, magenta, yellow, key/black) for print design.
How to use this tool
- Enter your red, green, and blue values (0–255).
- The tool outputs C, M, Y, K percentages for use in print design software.
- Note: CMYK is device-dependent; final print results depend on your printer profile.
Convert screen RGB colors to CMYK (Cyan, Magenta, Yellow, Key/Black), the color model used in professional printing.
Formula
Normalize: r' = R/255, g' = G/255, b' = B/255.
Key (black): K = 1 − max(r', g', b')
If K = 1 (pure black), then C = M = Y = 0. Otherwise:C = (1 − r' − K) / (1 − K)M = (1 − g' − K) / (1 − K)Y = (1 − b' − K) / (1 − K)
All four values are multiplied by 100 and rounded to express percentages.
How it works
CMYK is the subtractive color model used in color printing: Cyan, Magenta, Yellow, and Key (black) inks each absorb portions of white light. Converting from additive RGB to subtractive CMYK first extracts how much black ink is needed (the Key value), then scales the remaining color deficit for each channel into ink percentages. The black channel is separated out explicitly to save ink and produce sharper black text in real print workflows.
A common mistake is ignoring the pure-black edge case — when all RGB channels are 0, the formula for C, M, Y would divide by zero. The correct result is C = M = Y = 0, K = 100%, not an undefined or infinite value. Also note that this is a device-independent mathematical conversion; actual print results depend on the specific printer and ink profile used.
Worked example
Convert RGB (255, 0, 0) — pure red — to CMYK
- Normalize: r' = 1.0, g' = 0.0, b' = 0.0.
- K = 1 − max(1.0, 0.0, 0.0) = 1 − 1.0 = 0.0 → 0%.
- C = (1 − 1.0 − 0) / (1 − 0) = 0 → 0%; M = (1 − 0 − 0) / 1 = 1.0 → 100%; Y = (1 − 0 − 0) / 1 = 1.0 → 100%.
cmyk(0%, 100%, 100%, 0%)
Common mistakes to avoid
- Assuming RGB-to-CMYK conversion is fully reversible -- the two color models have different gamuts; some screen colors cannot be reproduced in print.
- Ignoring the K (black) channel and adjusting only CMY, producing muddy browns instead of true black.
- Using the raw CMYK percentages without a color profile -- print output depends on the ICC profile and paper stock; on-screen CMYK preview does not guarantee printed results.
Key terms
- CMYK
- A subtractive color model used in print: Cyan, Magenta, Yellow, and Key (black) inks absorb light, and their combination produces visible colors on white paper.
- Key (K)
- The black ink channel in CMYK, calculated as 1 minus the largest normalized RGB channel; separating black saves ink and improves text sharpness compared to mixing C+M+Y.
- Subtractive color mixing
- A system where adding ink or pigment removes (absorbs) wavelengths from reflected light, the opposite of additive RGB mixing used by screens.
- Device-independent conversion
- A mathematical transform between color spaces that does not account for a specific printer's gamut, dot gain, or ink profile — actual printed colors may vary.
Frequently asked questions
- Why is CMYK used for printing?
- Printers use subtractive color mixing — inks absorb light. CMYK inks combine to produce a wide range of colors on paper, unlike RGB which adds light.
- Is RGB-to-CMYK conversion exact?
- Not always. RGB and CMYK have different color gamuts. Some vivid screen colors cannot be reproduced in print.