Color Contrast Checker

How Color Contrast Checker works

Check the contrast ratio between text and background and see WCAG AA and AAA results. Everything happens inside this page: the tool reads your input, runs the calculation or conversion locally, and hands the result back to you. Nothing is transmitted, because there is no backend to transmit it to.

That design choice is deliberate. Most free tool sites upload your files to a server, process them there, and quietly keep a copy. Toolcin cannot do that — the site is a set of static files. If your connection dropped the moment the page finished loading, every tool would still work.

The WCAG ratio

Contrast is (lighter luminance + 0.05) ÷ (darker luminance + 0.05), which produces a ratio between 1:1 and 21:1. The +0.05 is not arbitrary — it accounts for ambient light reflecting off the screen.

Luminance is computed with the same perceptual weights used elsewhere: 0.2126 red, 0.7152 green, 0.0722 blue, after gamma correction.

The thresholds

WCAG AA requires 4.5:1 for normal text and 3:1 for large text (18 pt, or 14 pt bold). AAA raises that to 7:1 and 4.5:1. Interface components and focus indicators need 3:1 against their surroundings.

Where people stop measuring

A passing ratio is measured against a solid colour. Text over a gradient, a photo or a semi-transparent overlay must pass at its worst point, which is usually where the image is lightest.

And a passing ratio does not guarantee readability at small sizes — 4.5:1 is a floor, not a target.

Good to know

• Works offline once loaded, including on flights and in locked-down networks.
• No file size limit beyond your device's own memory.
• Free to use, with no account and no usage counter.
• Results are produced locally, so they are not logged or shared with anyone.

Questions