Turning ink percentages into screen color

Paste the four values from a print spec, a brand book or a Pantone bridge guide, and the tool gives you the RGB and HEX you need for a website, slide deck or app. The math is a single multiplication per channel:

channel = 255 × (1 − ink ÷ 100) × (1 − K ÷ 100)

Cyan reduces red, magenta reduces green, and yellow reduces blue. Black reduces all three equally.

Worked example: C0 M67 Y87 K15

K factor: 1 − 0.15 = 0.85
R = 255 × (1 − 0) × 0.85 = 216.75, rounded to 217
G = 255 × (1 − 0.67) × 0.85 = 71.53, rounded to 72
B = 255 × (1 − 0.87) × 0.85 = 28.18, rounded to 28

That gives rgb(217, 72, 28), or #D9481C. The steps panel next to the swatch repeats this for whatever you type.

Reference values

CMYK	RGB	HEX	What it is
100, 0, 0, 0	0, 255, 255	#00FFFF	Process cyan, formula version
0, 100, 100, 0	255, 0, 0	#FF0000	Red built from magenta + yellow
0, 0, 0, 100	0, 0, 0	#000000	Plain black
60, 40, 40, 100	0, 0, 0	#000000	Rich black: same on screen
75, 68, 67, 90	6, 8, 8	#060808	A "registration-style" near black

The last two rows show a quirk of the formula. Once K is 100%, every channel is multiplied by zero, so all rich-black recipes collapse to #000000. On paper they look noticeably different from plain K100. The formula has no way to show that.

How accurate is it?

It is accurate as arithmetic and only approximate as a visual match. Printed cyan is not the #00FFFF you see on screen: real process cyan ink measures much closer to a mid sky blue, roughly #00AEEF. The formula ignores the ink's actual color, the paper's whiteness, dot gain and the profile your printer used.

For a closer match, there are two better routes:

Brand guidelines often list official RGB and HEX values next to CMYK. When they exist, use them; the brand owner has already done the matching.
Measured values. A spectrophotometer reading of the printed piece, converted to Lab and then to sRGB, beats any formula. The color converter accepts lab() input if you have such a reading.

Total ink warning

If C + M + Y + K adds up to more than 300%, the tool shows a warning. That isn't a problem for the conversion itself, but it is useful when you are checking a spec someone sent you. Coated paper on an offset press usually tolerates roughly 300 to 340%, uncoated stock less, and newsprint around 240%. A spec at 380% may smear or take a long time to dry.

Pasting values

The paste field accepts most ways people write CMYK:

0, 67, 87, 15
0 67 87 15
cmyk(0%, 67%, 87%, 15%)
C0 M67 Y87 K15

It takes the first four numbers it finds, so labels and percent signs are fine. Values must be between 0 and 100. Some older software writes CMYK as fractions from 0 to 1. Multiply those by 100 before pasting.

When to use this, and when not to

Good uses:

building a web style guide from a print-first brand;
previewing roughly what a printed spec will look like;
making a slide or social graphic that sits next to a printed piece.

Less good:

matching a printed sample exactly (measure it instead);
converting photos (use your image editor's profile conversion, which handles every pixel with the right profile).

The reverse direction is on RGB to CMYK. For codes, HEX to CMYK shows the full three-step method. To check that the resulting RGB color is readable as text or as a background, run it through the contrast checker.

FAQ

Why does my converted color look brighter than the print?

Screens emit light and paper reflects it, so a screen color will almost always look more saturated. Process inks also cover a smaller range of colors than an sRGB display.

Does CMYK have a HEX code?

Not directly. HEX is a way of writing RGB. You convert CMYK to RGB first, then write the RGB values in hex, which is what this tool does.

Are CMYK values ever above 100?

No. Each ink is a percentage of full coverage, from 0 to 100.