APCA Contrast Calculator
Pick a text colour and a background and get the APCA lightness contrast score, with a plain-English note on which text sizes that score can carry.
APCA contrast
-108Lc
Excellent — suitable for any text, including thin and small fonts.
About this tool
The calculator implements APCA-W3, the perceptual contrast model being developed for WCAG 3. The number it returns is Lc, and it is signed: a positive score means dark text on a lighter background, a negative one means light text on a darker background. The magnitude is what you read.
Under the score you get the practical reading — roughly 90 and above works for anything including thin small type, 75 is the sensible floor for body copy, 60 covers larger or bold text, and 30 is about the minimum for non-text elements like icons and dividers.
Everything runs in your browser — nothing you enter here is sent to a server or stored. Provided as is, without warranty.
Why APCA gives a different answer to WCAG 2
WCAG 2 treats contrast as a ratio between two luminance values. It is symmetric, so swapping the text and background colours gives you the same number. Human vision does not work that way. Light text on a dark background looks thinner and spreads slightly at the edges, an effect the older formula is completely blind to. APCA is directional by design, which is why the score flips sign when you swap the two fields.
It also takes font size and weight seriously rather than splitting the world into “normal” and “large”. The full APCA specification publishes a lookup table where required Lc falls as size and weight rise. The rule of thumb built into this tool is a simplification of that table, but it is the right simplification for the decisions you actually make: is this colour safe for paragraphs, safe only for headings, or safe only for decoration.
The practical caveat: APCA is not yet a legal or procurement standard anywhere. WCAG 3 is still a working draft and has been for years. If you have an accessibility clause in a customer contract, a public-sector tender, or a VPAT to fill in, the thing being audited is WCAG 2.1 AA, so run those numbers through the WCAG contrast checker as well. Use APCA to make better design decisions, use WCAG 2.1 to satisfy the paperwork, and where they disagree, pick the colour that clears both.
Dark interfaces are where the divergence shows up most. A muted grey on near-black that scrapes past 4.5:1 will often land around Lc 55 to 60, which the perceptual model correctly flags as headings only. If you are building a dark product UI and want it to hold up, APCA is the more honest of the two models. Test your secondary and tertiary text colours here first, then check whether they still clear the older thresholds.
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