Why is the LAB result approximate for print colors?

CMYK describes print pigments and LAB is derived via the sRGB screen model. The conversion passes through RGB as an intermediate step, so some print colors—especially highly saturated ones—may fall outside the sRGB gamut and cannot be represented exactly on screen.

What is the Key (K) channel in CMYK?

K stands for Key, which represents black ink. A dedicated black channel produces deeper blacks and reduces overall ink cost compared to mixing equal amounts of Cyan, Magenta, and Yellow.

What do L*, a*, and b* mean?

L* is perceptual lightness (0 = black, 100 = white). a* runs from negative (green) to positive (red). b* runs from negative (blue) to positive (yellow). The LAB color space is designed so that equal numerical distances correspond to approximately equal perceived color differences.

What illuminant does this tool use?

This tool uses the CIE D65 standard illuminant (daylight, 6500 K), with reference white Xn=0.95047, Yn=1.00000, Zn=1.08883. D65 is the default for sRGB and is the most common choice for web and display color work.

What does K=100 produce in LAB?

K=100 with any C, M, Y values produces pure black: lab(0 0 0). All channels at 0 produce pure white: lab(100 0 0).

Does this tool send my data anywhere?

No. All conversion math runs entirely in your browser using JavaScript. No data is sent to any server.

CMYK to LAB Converter

Name: CMYK to LAB Converter
Availability: InStock
Author: Nham Vu

Enter CMYK percentages and instantly get the equivalent CIE LAB (L*, a*, b*) values with a live color preview swatch.

CMYK Input

Cyan (C) 0%

Magenta (M) 45%

Yellow (Y) 100%

Key / Black (K) 0%

rgb(255, 140, 0)

CIE LAB Output

L* (Lightness)

a* (green–red)

b* (blue–yellow)

Conversion Steps

1 CMYK → RGB: R=255, G=140, B=0
2 RGB → Linear RGB (sRGB gamma): Rl=0.9888, Gl=0.2582, Bl=0.0000
3 Linear RGB → XYZ (D65): X=0.4877, Y=0.3612, Z=0.0451
4 XYZ → LAB: lab(66.89 24.48 74.99)

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Summary

Enter CMYK percentages and instantly get the equivalent CIE LAB (L*, a*, b*) values with a live color preview swatch.

How it works

Enter Cyan, Magenta, Yellow, and Key (Black) percentages (0–100) in the input fields or drag the sliders.
CMYK is first converted to RGB: R = 255 × (1−C/100) × (1−K/100), G = 255 × (1−M/100) × (1−K/100), B = 255 × (1−Y/100) × (1−K/100).
Each RGB channel is linearized by reversing the sRGB gamma curve (IEC 61966-2-1).
Linear RGB is multiplied by the standard sRGB→XYZ (D65) matrix to produce X, Y, Z tristimulus values.
XYZ is normalized against the D65 reference white (Xn=0.95047, Yn=1.00000, Zn=1.08883) and transformed via the CIE f() function into L*, a*, b*.
A color swatch previews the exact resulting color using the intermediate RGB.
Click "Copy LAB" to copy the lab() CSS string, or "Copy RGB" for the intermediate rgb() value.

Use cases

Translate print-spec CMYK colors into device-independent CIE LAB values for color matching.
Cross-reference brand color specifications between print and perceptual color science workflows.
Convert CMYK values from design files into LAB for color-difference (ΔE) calculations.
Validate that a print color matches the intended perceptual appearance on screen.
Build LAB color palettes from existing CMYK brand guides.
Prepare color data for ICC profile creation or color management pipelines.
Quickly estimate perceptual lightness (L*) and chroma (a*, b*) for a given ink mix.
Generate lab() values for CSS Color Level 4 without a preprocessor.

Frequently Asked Questions

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Last updated: 2026-05-28 · Reviewed by Nham Vu