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

Why CMYK uses a separate black channel

The most obvious way to print black would be to combine 100% cyan, 100% magenta, and 100% yellow. In practice, this does not work well. Mixing three ink colors at full density produces a dark, muddy brown rather than a clean black, because real inks are impure and their absorbance curves overlap imperfectly. It also uses three times as much ink as printing with pure black, which is expensive, takes longer to dry, and can saturate paper to the point of warping.

The Key (black) plate solves all three problems: it produces sharper, denser black text and line art; it uses a single ink; and it lets the printer reduce the total ink coverage on dark areas by replacing CMY density with K density. The conversion formula extracts the maximum channel value as the black component and then calculates how much additional color each channel needs after removing that shared darkness.

Profile-free conversion: what that means in practice

This converter uses the standard arithmetic RGB-to-CMYK formula with no ICC color profile. The formula is device-independent and will give the same result for a given RGB value every time, but it does not account for how any specific printer or press will actually reproduce that color.

Real-world CMYK printing involves device profiles that map color values to the specific ink, paper, and rendering intent of a particular press. A “vivid blue” on an offset press may need different CMYK percentages than the same perceptual blue on a desktop inkjet, because the inks and paper interact differently.

Use this converter to:

• Get a starting-point CMYK value for use in design software
• Check rough color relationships between RGB values
• Understand the CMYK model and verify conversions manually

Do not use it as the final specification for a professional print job. For that, apply an ICC output profile in your design application (Adobe Illustrator, InDesign, Photoshop) and convert in a color-managed workflow before sending to the printer.

Common CMYK reference values

Note that neutral grays always have 0% CMY and vary only in K, because they contain no hue component to separate into individual ink channels.

The whole calculation runs in your browser — nothing is uploaded.