CMYK to RGB Converter

CMYK is subtractive: cyan, magenta and yellow inks each absorb part of the white light reflected from paper, and black (K, for key) adds depth and saves colored ink. The four numbers say how much of each ink covers the paper, from 0 to 100 percent; 0/0/0/0 is bare paper, and every ink added makes the result darker.

RGB is additive: a screen starts black and adds red, green and blue light, each from 0 to 255; 255/255/255 is white. HEX is the same three numbers written in base 16, and HSL rewrites them as hue, saturation and lightness. A CMYK color therefore has no single RGB equivalent: the answer depends on which inks, which paper and which screen are meant.

CMYK values come from print-ready files (InDesign and Illustrator swatches, PDF/X exports), from a printer's specification, or from a brand guide that lists PANTONE®, CMYK, RGB and HEX side by side. That last case is the usual reason for this conversion: the guide has a CMYK value, and the web designer needs a HEX.

With C, M, Y and K as fractions from 0 to 1: R = 255 × (1 − C) × (1 − K), G = 255 × (1 − M) × (1 − K), B = 255 × (1 − Y) × (1 − K), each rounded to the nearest whole number. It assumes ideal inks that each absorb exactly one of the three lights, and paper that reflects everything, which is why the CSS color specification calls the same calculation the naive conversion for device-cmyk().

Example: C 70, M 20, Y 0, K 10. R = 255 × 0.30 × 0.90 = 68.85 → 69; G = 255 × 0.80 × 0.90 = 183.6 → 184; B = 255 × 1.00 × 0.90 = 229.5 → 230. The result is rgb(69, 184, 230), HEX #45b8e6.

The formula loses information at the dark end: every color with K = 100 becomes #000000, so 0/0/0/100 (plain black) and 60/40/40/100 (a rich black) come out identical, although on paper the rich black is visibly deeper.

Adobe applications convert through an ICC profile that describes real inks on real paper: U.S. Web Coated (SWOP) v2 by default in North America, Coated FOGRA39 in Europe, Japan Color 2001 Coated in Japan. Real cyan ink is not the exact opposite of red light, so 100 percent cyan through the SWOP profile is about #00aeef, a sky blue, rather than the formula's #00ffff, and 100 percent black alone is the dark grey #231f20, not #000000. The profile also knows that the paper is not perfectly white and that inks overprint imperfectly.

Neither answer is wrong. The formula is the device-independent reference that web calculators, spreadsheets and CSS tools share, and it is what people mean when they quote a CMYK-to-RGB value without naming a profile. The profile answer is what the job will look like on that press and paper, and it is the one to use for a brand color, a packaging mock-up or a soft proof.

The classic Illustrator swatch conversions, with the SWOP profile, next to the formula:

The two gamuts overlap only partly. sRGB cannot show a process cyan or yellow at full strength, and print cannot reproduce the saturated greens, oranges and blues a screen makes easily, which is why a bright #00ff00 comes back from a press as a muted green whatever the numbers say. Total ink coverage adds a second limit: presses cap the sum of the four percentages, typically 300 percent for SWOP, 330 for FOGRA39 coated stock and around 240 for newsprint, so 100/100/100/100 is a registration mark, not a printable color.