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RGB to CMYK Converter

Convert a screen RGB colour into its CMYK print percentages — cyan, magenta, yellow and black — right in your browser. A fast, profile-free approximation for getting from screen to press.

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Quick Answer

Enter an RGB colour (for example 37, 99, 235) and the tool returns the matching CMYK percentages — the cyan, magenta, yellow and black inks used in four-colour printing. It applies the standard algebraic formula, deriving black (K) from the brightest channel. Because there is no printer ICC profile involved, read the result as a close approximation for screen-to-print planning, not a colour-managed proof. Everything runs in your browser.

What the RGB to CMYK Converter Does

This converter takes a colour described the way a screen describes it — red, green and blue from 0 to 255 — and restates it in the four inks a printing press uses: cyan, magenta, yellow and a separate black, each as a percentage from 0 to 100. You type the RGB triple, and the CMYK percentages appear instantly, alongside a swatch of the colour.

It is the quick way to answer a practical question: roughly how much of each ink makes this on-screen colour? That helps when you are setting ink values in a layout, sanity-checking a design before it goes to print, or simply learning how the two colour models relate.

How It Works

RGB and CMYK are opposite kinds of colour. RGB is additive — it starts from black and adds red, green and blue light to build brighter colours, the way a screen does. CMYK is subtractive — it starts from white paper and adds inks that absorb light, so more ink means a darker result. Converting between them means moving from one logic to the other.

The tool first works out the black component (K) from the brightest of the three channels: the darker the colour, the more black it needs. It then calculates how much cyan, magenta and yellow remain once that black is accounted for, and rounds each to a whole percentage. The maths is exact and repeatable — what it does not include is any knowledge of your specific printer, ink or paper.

Data source & conversion logic

  1. Read the RGB values. Take the three numbers (red, green, blue), each from 0 to 255, and scale them to a 0-to-1 range by dividing by 255.
  2. Find the black (K). Black is 1 minus the largest of the three scaled channels, so a bright colour gets little black and a dark colour gets a lot.
  3. Work out C, M and Y. For each channel, take how far it falls short of full, remove the black already counted, and divide by what black leaves behind.
  4. Convert to percentages. Multiply all four values by 100 and round to whole numbers — the cyan, magenta, yellow and black percentages.

RGB to CMYK

K = 1 − max(R, G, B) ÷ 255 C = (1 − R÷255 − K) ÷ (1 − K) M = (1 − G÷255 − K) ÷ (1 − K) Y = (1 − B÷255 − K) ÷ (1 − K) then multiply each by 100 and round to a whole percent
Worked example
RGB 37, 99, 235 → C 84% M 58% Y 0% K 8%

Black comes from the lightest channel. Pure white (255, 255, 255) gives 0 for all four; pure black (0, 0, 0) gives K 100% and the rest 0.

Standards & references

  • RGB and CMYK colour models — RGB mixes red, green and blue light (additive, used by screens); CMYK layers cyan, magenta, yellow and key/black inks (subtractive, used by print). The two describe colour in fundamentally different ways.
  • ICC colour profiles — An ICC profile is a file that describes how one specific device reproduces colour under set conditions — a given press, ink and paper. Accurate print conversion runs the colour through such a profile; this tool does not, so its output is device-independent maths.
  • Gamut — The range of colours a device can show. A screen's RGB gamut is wider than a press's CMYK gamut, so some vivid screen colours simply cannot be printed and come out duller.

Accuracy & Limitations

The formula is exact and matches other simple converters, but simple is the operative word: it treats every ink and paper as identical, which no real press is. Use it for a sensible estimate, not a guaranteed match.

Bright, saturated RGB colours — electric blues, neon greens, pure magentas — often sit outside the CMYK gamut. On paper they get pushed to the nearest printable colour and look more muted than they did on screen. The converter cannot warn you which colours those are.

Because there is no ICC profile, the result is not colour-managed. The same CMYK percentages will look different on glossy versus uncoated stock, or on two different presses. For anything colour-critical, your print shop's profile is what matters.

Black is generated from the lightest channel (a basic GCR-style approach). Professional separations often distribute black differently for richer shadows or ink savings, so a press-ready file may show different numbers for the same visible colour.

Real-World Use Cases

Planning a print colour

Get a rough CMYK starting point for a colour you designed on screen.

Setting ink values

Fill in cyan, magenta, yellow and black fields in a layout app with sensible numbers.

Learning colour models

See how a screen RGB colour maps onto print inks and why black is separate.

Quick sanity check

Spot when a vivid screen colour will need toning down for print.

When to use it — and when not to

Good for

  • A quick screen-to-print colour estimate
  • Picking approximate ink percentages
  • Understanding how RGB relates to CMYK
  • Checking whether a colour is print-friendly

Not the best choice for

  • Colour-critical or brand-exact printing
  • A press-ready, colour-managed proof
  • Matching a Pantone or spot colour
  • Knowing the exact on-paper result

For print-accurate colour, convert through your print shop's exact ICC profile in a colour-managed app such as Photoshop, Illustrator or Affinity — or send them your RGB file and let them separate it. For brand colours, match to a Pantone reference rather than a CMYK guess.

Frequently Asked Questions

How accurate is this RGB to CMYK conversion?
It is mathematically exact for the standard formula, but that formula ignores the printer, ink and paper. Think of it as a close estimate for planning, not a colour-managed result. For print that has to match, use your shop's ICC profile.
Why does my bright colour look duller in CMYK?
Screens (RGB) can show more saturated colours than ink on paper (CMYK) — a wider gamut. Colours outside the printable range get mapped to the nearest ink mix, which is less vivid. That gap is physical, not a tool error.
What is the K in CMYK?
K is the key plate — black ink. It is separate from cyan, magenta and yellow because mixing those three never makes a clean, deep black, and a dedicated black ink gives crisper text and richer shadows while using less coloured ink.
What is an ICC profile and why does it matter?
It is a file describing how a specific device reproduces colour under set conditions. A colour-managed conversion runs your colour through the target press's profile so the printed result matches expectations. Without one — as here — the conversion is just generic maths.
Can I convert CMYK back to the same RGB?
Not exactly. The round trip is lossy because the two models do not overlap perfectly and rounding occurs both ways. You will usually land close to, but not exactly on, the original RGB.
Why are some values 0%?
A channel reads 0% when that ink is not needed. A pure, bright blue, for example, needs no yellow, so yellow shows 0. White needs no ink at all, so all four are 0.
Does it support a percentage RGB input?
Enter RGB as the usual 0-to-255 numbers (for example 37, 99, 235). The tool reads those three values and converts; it does not expect 0-to-100 percentages for the RGB side.
Is this the same conversion my design app uses?
No. Design apps use colour-managed, profile-aware conversions that account for the destination press. This tool uses the simple algebraic formula, so the numbers can differ — especially for saturated colours.
What is total ink coverage and does this show it?
Total ink coverage is C plus M plus Y plus K added up; presses often cap it (commonly around 240 to 300 percent) to avoid over-inking. This tool shows the four values but does not enforce or flag a coverage limit.
Will this match a Pantone or spot colour?
No. Pantone colours are pre-mixed spot inks with their own references. A CMYK approximation may look similar but is not a Pantone match — use an official Pantone-to-CMYK bridge or a swatch book for that.
Is anything uploaded?
No. The conversion is plain arithmetic done in your browser; nothing is sent anywhere.
Why does my print look different on glossy versus matte paper?
The same CMYK percentages absorb and reflect differently depending on the paper. Glossy stock tends to look more saturated, uncoated more muted. That is exactly what an ICC profile captures and a profile-free formula cannot.

References

Uses the standard algebraic RGB-to-CMYK formula, with black taken from the lightest channel; it is honest that without an ICC printer profile the result is an approximation, not a colour-managed print conversion.

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