Comparison
RGB vs CMYK
One model adds light, the other removes it. That is not a detail — it changes which colors are reachable and which conversions can be trusted.
Short answer. Design in RGB and convert to CMYK only at the end, using a profile for the actual press — a formula-based conversion is fine for a mockup and should never be the file you send to print.
RGB is additive: a display starts black and emits red, green and blue light, and more of each gets you closer to white. CMYK is subtractive: paper starts white and each ink absorbs part of the spectrum, so more of each gets you closer to black. The two run in opposite directions, which is why their gamuts are different shapes rather than one simply being a subset of the other.
Most of what is reachable in sRGB is reachable in CMYK, but the exceptions are the ones people notice: bright saturated blues, vivid oranges and anything approaching a screen green print dull. Conversely, some CMYK colors — certain deep cyans, and anything using a spot ink — cannot be represented in sRGB at all.
The part that matters most in practice: a correct RGB to CMYK conversion needs an ICC profile describing a specific press, ink set and paper stock. That is measured information no formula has. The converter on this site, like every formula-based converter, uses the naive transform. It is useful for approximating a shift and for spotting colors print cannot reach. It is not a proof and it is not a deliverable.
RGB vs CMYK, side by side
| Dimension | RGB | CMYK |
|---|---|---|
| Model | Additive — emitted light | Subtractive — absorbed light |
| Channels | Red, green, blue | Cyan, magenta, yellow, key (black) |
| Starting point | Black; adding light brightens | White paper; adding ink darkens |
| Typical medium | Screens | |
| Gamut strengths | Saturated blues, greens, cyans | Some deep cyans; spot inks beyond sRGB entirely |
| Gamut weaknesses | Cannot show some print colors | Cannot reach screen-bright blues, oranges, greens |
| Conversion accuracy | — | Requires an ICC profile; formulas approximate |
| CSS support | Native | None — not a web color model |
Where this comparison is unfair
The black plate is not a simple fourth channel. How much of a neutral is built from K versus from equal parts CMY — grey component replacement, and total ink limits — is a decision the press profile makes, and it changes both the appearance and the cost. A naive conversion has no view on any of it.
If colour fidelity across screen and print genuinely matters, the answer is not a better formula. It is a soft proof through the actual output profile, and ideally a physical proof from the actual press.
Frequently asked questions
What is the difference between RGB and CMYK?
RGB is additive and describes emitted light on a screen; CMYK is subtractive and describes ink absorbing light on paper. They run in opposite directions and reach different sets of colors, so neither gamut fully contains the other.
Why do my colors look different when printed?
Usually because a saturated screen color is outside what the press can reach and has been mapped to the nearest printable one — bright blues and vivid greens are the common casualties. Sometimes it is also the paper: an uncoated stock absorbs more ink and prints noticeably flatter.
Can I convert RGB to CMYK accurately without a profile?
No. Accurate conversion requires an ICC profile characterising the specific press, ink and paper, which is measured data no formula contains. A formula-based conversion approximates the shift well enough for a mockup and nothing more.
Should I design in RGB or CMYK?
Design in RGB and convert at the end. RGB has the wider working gamut and every editing tool is faster in it; converting early throws away color you cannot get back, and locks you to one output profile before you know which press will run the job.
Try it yourself
Definitions
- CMYKCMYK is the subtractive four-ink model used in printing — cyan, magenta, yellow and a black key plate.
- GamutA gamut is the set of colors a given device or color space can actually produce.
- ICC profileAn ICC profile is a file describing the color behaviour of a specific device, used to convert colors between devices accurately.
- sRGBsRGB is the default color space of the web: a specific set of red, green and blue primaries plus a transfer function that says how the stored numbers map to emitted light.
Other comparisons
- OKLCH vs HSLBoth are cylindrical: a hue angle, a colourfulness axis and a lightness axis. Only one of them measures lightness in a way your eye agrees with.
- WCAG contrast vs APCAOne is the standard you will be measured against. The other is the better model of what your eye is doing. You need both, for different reasons.
- Lab vs OKLabSame shape: a lightness axis and two opponent axes. Forty-four years apart, and fitted to different data.
- HEX vs RGBThis is not a question about color. Both are sRGB, both carry exactly the same information, and every hex code has an identical rgb() form.
- sRGB vs Display P3P3 covers around 25% more area than sRGB. Almost all of it is in the reds, oranges and greens; there is very little extra blue.