Result
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Facts and limits of this method
| Red formula | R = 255 × (1 − C/100) × (1 − K/100) |
|---|---|
| Green formula | G = 255 × (1 − M/100) × (1 − K/100) |
| Input range | C, M, Y, K from 0% to 100% |
| Output range | R, G, B from 0 to 255 |
When it misleads you
- This is a mathematical approximation, not the output of an actual printer's color profile — a real print may look different due to inks, paper and equipment.
- CMYK is a subtractive model for print, RGB is additive for screens; converting between them always loses some accuracy relative to how the color will actually look on paper.
- The formula assumes the simplest ink-mixing scheme with no ICC profile — for color-critical print jobs use dedicated software.
- Rounding of percentages and RGB byte values can shift the resulting shade slightly if you convert back and forth repeatedly.
How it is calculated
The C, M, Y and K percentages are converted to fractions from 0 to 1 by dividing by 100.
For each of R, G, B, the product (1 − color fraction) × (1 − black fraction) is computed, representing how much light remains uncovered by ink.
The result is multiplied by 255 and rounded to a whole number, giving standard 8-bit R, G, B values.
A HEX code and an rgb(...) text string are also assembled from R, G, B for convenient use in CSS.
Questions and answers
Why doesn't the on-screen color match what actually prints?
A screen shows light (RGB), while paper shows reflected light after ink is applied (CMYK); an exact match needs a profile for the specific printer and paper.
Can I use the result as a final design color?
Yes, as a guideline for interfaces and digital layouts — it's accurate enough for most everyday tasks.
Why do the numbers differ slightly after RGB→CMYK→RGB round-tripping?
Rounding of CMYK percentages and RGB byte values accumulates a small error at each step.
Is my data sent anywhere?
No, the whole calculation runs in your browser.