Convert a hex code to the four CMYK inks

First turn the code into three numbers, then turn those numbers into four ink percentages. The code #3B82F6 is three pairs of characters: 3B, 82 and F6. Each pair is a number written in hexadecimal, where the letters A to F stand for 10 to 15 after the digits 0 to 9. So 3B means 3 × 16 + 11, which is 59, 82 is 130, and F6 is 246.

The formula: K = 1 − (largest channel ÷ 255), then C = (1 − R ÷ 255 − K) ÷ (1 − K). Magenta comes from the green channel in the same way, and yellow from the blue one.

In #3B82F6 the blue channel is the brightest. 246 ÷ 255 is 0.965, so black comes out at 0.035, or 4%. Cyan is 76%, magenta 47% and yellow 0%, because the blue channel is the one that set black. The result is cmyk(76%, 47%, 0%, 4%).

You get the same answer in two steps with the HEX to RGB converter and then the RGB to CMYK converter. To go from the CMYK values in a brand guide back to a code, use the CMYK to HEX converter.

A hex code describes a screen color in base 16. The six characters after the hash sign make three pairs for red, green and blue light, and each pair runs from 00 to FF, which is 0 to 255. Upper and lower case mean the same thing. CSS also accepts a three-character shorthand, where every character is doubled, so #38F is #3388FF, and an eight-character form whose last pair sets transparency[1]. Six characters give 256 × 256 × 256 combinations, which is 16,777,216 colors[2]. You can pull the hex codes out of any photo with the image color extractor.

CMYK describes a color as ink. The four numbers are the share of the paper covered with cyan, magenta, yellow and black, where K stands for the key plate[3]. Zero means bare paper and 100 means full coverage.

The two scales run in opposite directions. A screen gives off light, so higher pairs in a hex code make a lighter color. Paper reflects light and ink absorbs it, so higher CMYK numbers make a darker color. Ink has no transparency either, which is why the converter ignores the last pair of an eight-character code.

If your color is in another format, such as OKLCH, Lab or Android code, the color converter shows it in every format at once.

The formula assumes perfect inks, while design software works with an ICC profile, a description of a specific set of inks, paper and press. You see the gap most clearly on black and gray. The formula always leaves at least one of the three color inks at zero and hands all of the gray to black ink, so #808080 becomes 50% black and nothing else. A press profile builds the same gray from all four inks.

Two widely used press profiles show how far apart the rules can be. GRACoL 2013, published by Idealliance, allows up to 320% total ink and uses black up to 100%[4]. PSO Coated v3 from the European Color Initiative caps total ink at 300% and stops black at 96%[5]. The profile for your job is in your printer's file specifications.

When you need numbers for a print file, open the Adobe Color Picker in Photoshop by clicking the foreground color box in the toolbox, then type the code in the # text box. The picker shows the C, M, Y and K values at the same time[6], and they follow the CMYK working space set under Edit › Color Settings[7]. If a warning triangle appears next to the swatch, the color is out of gamut for the inks, and clicking the triangle picks the closest printable match[6].