← DictionaryContrast Ratio
The measured difference in luminance between text and its background.
Whether text is dark enough against its background to read.
What It Is
Contrast Ratio is a Website item, filed under Standards. What it actually refers to is the measured difference in luminance between text and its background.
It is something measured and compared over time, so one reading in isolation tells you almost nothing. That definition is deliberately narrow — the narrowness is what makes it usable.
How It's Used
Most of the time Contrast Ratio is used in site builds, page structure and the technical decisions underneath them. It rarely travels alone — expect it next to Accessibility, WCAG and Colour Palette. The practical test is whether it is measured the same way each period, against something.
Why It Matters
Ignoring Contrast Ratio rarely fails loudly — it fails slowly. When it is unclear, the site still launches — it just quietly underperforms. The businesses that treat it seriously spend less time redoing work.
Think of a weighing scale — useful because you step on it more than once. Whether text is dark enough against its background to read.
Termshift™
How the meaning shifts depending on who is using it, and where.
In agency and in-house rooms, Contrast Ratio means exactly the measured difference in luminance between text and its background.
In plain conversation it comes out as whether text is dark enough against its background to read.
The Bottom Line
Contrast Ratio pays off when it is specific and costs you when it is not. Whether text is dark enough against its background to read.