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APCA Contrast Checker

Calculate the APCA lightness contrast (Lc) for any text and background pair, with the draft WCAG 3 font size and weight lookup and a live preview.

Text colour
Background colour

APCA lightness contrast

Large heading, 36px

Content text at 18px, weight 400.

Small bold text at 14px, weight 700.

98.2
APCA Lc
Dark on light
Polarity
13.98:1
WCAG 2.1 ratio

What is actually readable at this Lc

Lc 98.2 clears the Lc 90 level. Preferred for body text and any small or thin text. Smallest sizes that the draft lookup allows here: 14px / 700, 15px / 400 and up.
LcUseSmallest font / weight
90Preferred for body text and any small or thin text14px / 700, 15px / 400 and up
75Minimum for columns of body text16px / 400, 14px / 700, 24px / 300
60Minimum for content text you expect people to read18px / 400, 16px / 500, 24px / 300
45Minimum for large headings and sub-headings24px / 400, 21px / 500, 36px / 300
30Absolute minimum for any text — plus icons and UI outlines36px / 400, 24px / 700
15Invisibility floor — decorative, non-informational elements onlyNot for text

APCA is a draft of WCAG 3 and is not a legal conformance requirement anywhere today. If you have to certify against WCAG 2.1 or 2.2, use the ratio shown above and its 4.5:1 / 3:1 thresholds. This table follows the APCA-W3 0.1.9 “bronze simple mode” guidance.

Screen luminance behind the score

0.01230
Text Y (screen luminance)
0.95104
Background Y

APCA raises each channel to the power 2.4 and weights them 0.2126 / 0.7152 / 0.0722, then applies a soft clamp below Y 0.022 so very dark colours do not run away. Because the curve is polarity dependent, dark text on a light background and light text on a dark background score differently even when the WCAG ratio is identical.

What is the APCA Contrast Checker?

APCA is the contrast method drafted for WCAG 3, and it fixes a real problem with the old ratio: WCAG 2.

  • APCA-W3 0.1.9 Lc score with correct polarity handling
  • Font size and weight lookup for each readability level
  • Live preview at heading, content and small-text sizes
  • WCAG 2.1 ratio shown alongside for conformance work
  • Exposes the screen luminance figures behind the score
  • Runs fully offline in your browser

How to use the APCA Contrast Checker

  1. 1

    Enter your text colour and your background colour, in that order — polarity matters.

  2. 2

    Use the Swap button to check the reversed pairing without retyping.

  3. 3

    Read the Lc value and check the live preview block at 36px, 18px and 14px.

  4. 4

    Find your Lc in the lookup table to see the smallest font size and weight that stays readable.

About the APCA Contrast Checker

APCA is the contrast method drafted for WCAG 3, and it fixes a real problem with the old ratio: WCAG 2.1 treats dark-on-light and light-on-dark as identical, when your eye does not. APCA is polarity-aware, so it returns a positive Lc for dark text on a light background and a negative one for the reverse.

The score comes from screen luminance — each channel raised to the power 2.4 and weighted 0.2126, 0.7152 and 0.0722 — with a soft clamp applied to very dark values so near-blacks do not run away, then a polarity-dependent power curve. This implementation uses the APCA-W3 0.1.9 constants and reproduces the published black-on-white value of Lc 106.

APCA is still a draft and is not a legal conformance requirement anywhere, so the WCAG 2.1 ratio is shown alongside for anything you have to certify. Everything runs locally in your browser with no uploads.

Frequently asked questions

What is a good APCA Lc value?

Lc 75 is the working minimum for columns of body text, and Lc 90 is preferred for anything small or thin. Lc 60 suits larger content text, Lc 45 covers headlines, and below Lc 30 nothing should carry information. The sign only tells you the polarity, not the quality.

Why is my APCA score negative?

A negative Lc means light text on a dark background. That is not a failure — judge it by the absolute value. APCA deliberately separates the two polarities because a light-on-dark pairing needs different treatment to read as well as its dark-on-light mirror.

Should I use APCA or the WCAG 2.1 contrast ratio?

If you have a legal or contractual obligation, use WCAG 2.1 or 2.2 and its 4.5:1 and 3:1 thresholds — APCA is a draft and confers no conformance. Use APCA as a design aid when the old ratio gives an answer that clearly disagrees with what you can see.

Why does APCA disagree with the WCAG contrast ratio?

The two model the eye differently. WCAG 2.1 uses a simple luminance ratio that ignores polarity and font size, and it is known to be too lenient with dark backgrounds and too strict with some light pairings. APCA folds in polarity and the spatial characteristics of text.

Is APCA part of WCAG 2.2?

No. WCAG 2.2 kept the 2.1 contrast ratio unchanged. APCA is being developed for WCAG 3, which is still a working draft with no confirmed publication date, so treat these numbers as guidance rather than a standard.

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