Convert RGB to CMYK, Free
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How to convert RGB to CMYK
RGB (Red, Green, Blue) is the additive color model used by screens. CMYK (Cyan, Magenta, Yellow, Key/Black) is the subtractive color model used in print. Converting RGB to CMYK is necessary when preparing digital designs for professional printing: the color gamuts differ, and a design that looks vivid on screen may appear duller in print if the conversion is not done correctly.
This converter applies the standard mathematical conversion from RGB to CMYK. Note that the resulting CMYK values are device-independent approximations. For critical print work, always proof with an ICC color profile specific to your printer and paper stock.
Enter the RGB values
Type the Red, Green, and Blue values, each in the range 0 to 255. For example, a pure red is R:255, G:0, B:0.
Read the CMYK result
The converter displays Cyan, Magenta, Yellow, and Key (Black) percentages. Pure red (255,0,0) = C:0%, M:100%, Y:100%, K:0%.
Apply to your print file
Enter the CMYK percentages into your design software (Illustrator, InDesign, Photoshop) for each color you are converting.
Proof before printing
CMYK output varies by printer, ink, and paper. Always request a physical or PDF proof from your printer before a full print run.
Frequently asked questions
Why do RGB colors look different when converted to CMYK?
The CMYK gamut is smaller than sRGB. Highly saturated RGB colors, especially bright greens and blues, fall outside the CMYK gamut and must be mapped to the nearest printable equivalent, which is less vivid.
What is the formula for RGB to CMYK?
First normalize: r = R/255, g = G/255, b = B/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). Multiply by 100 for percentages.
Is this converter accurate enough for professional printing?
It is accurate for the mathematical formula. For professional printing, use ICC profiles and soft-proofing in a calibrated application. The formula alone does not account for paper and ink variation.
What is the K (Black) channel in CMYK?
K stands for Key (not Black) because it is the key plate in offset printing. In practice it is black ink. Using a separate black channel produces crisper text and uses less ink than mixing CMY to make near-black.