Convert CMYK values into an RGB color

Subtract each ink from one, multiply by the same for the black, and multiply by 255. Percentages go into the formula as fractions, so 76% enters it as 0.76.

Formula: R = 255 × (1 − C) × (1 − K), and the green and blue channels work the same way, from magenta and from yellow.

The color cmyk(76%, 47%, 0%, 4%) gives 255 × 0.24 × 0.96 on the red channel, which is 59. Green comes out at 130 and blue at 245, because there is no yellow ink in this color at all. The result is rgb(59, 130, 245).

A few values come up more often than the rest. Black alone at 100% gives rgb(0, 0, 0), four zeros give white, and black at 20% gives the gray rgb(204, 204, 204), that is the code #CCCCCC.

CMYK values are given in whole percentages, so on the way there and back a channel can land one step off. That difference is invisible on screen. To take a screen color to ink, use the RGB to CMYK converter.

The four CMYK numbers say how much ink should land in a given place. The first is cyan, the second magenta, the third yellow and the fourth the black, written as K. Each is a percentage of coverage: zero means bare paper and a hundred means full coverage.

Inks take light away from white paper, so four zeros give white and rising values lead to a steadily darker color. That has a consequence: CMYK values belong to a particular paper and a particular ink, because the same mix comes out one way on coated stock and another on uncoated[1].

The three RGB numbers describe something else: the strength of emitted light. The red, green and blue channels take values from 0 to 255 and a screen adds their light together, so three zeros give black and three maximum values give white.

A screen has one shared scale for all of this: the sRGB space, which holds for HTML and CSS[2]. That is why a color given in RGB looks the same on every compliant device, while the same color laid down in ink depends on what it was printed on and with.

Brand books usually come together with printed material, so they describe color the way a press needs it: as four ink shares. A website needs the same color as three numbers or as a HEX code. Type the four values into the converter at the top of the page and you get notation ready to paste into a stylesheet.

Treat the result as a starting point and compare it with a printed sample if you have one to hand. The four numbers describe ink on a particular paper while a screen emits its own light, so the two versions of a color always differ a little. What matters for a website is that the shade is recognizable and consistent with the rest of the identity.