Color · Accessibility
APCA contrast checker.
Pick a text color and a background color and get the APCA lightness contrast (Lc) beside the WCAG 2.2 contrast ratio. The two are different measures and can disagree. Runs in your browser; nothing is sent or stored.
Short answer: APCA reports Lc from 0 to about 106 (negative for light text on a dark background), and it depends on which color is the text. WCAG 2.2 reports a ratio from 1:1 to 21:1 that ignores polarity. APCA is a draft and is not a WCAG 2 conformance method: to claim WCAG 2.2 conformance, the 4.5:1 / 3:1 ratio tests are the ones that count. Use Lc as extra design guidance.
Colors
Result
Body text sample (16px) — AaBbCc
Bold sample (24px)
APCA Lc levels by use
WCAG 2.2 ratio tests
APCA is not a WCAG 2 conformance method. Lc levels are draft guidance from the APCA authors.
Worked example
Mid-gray #767676 text on white: WCAG 2.2 ratio 4.54:1, which passes the 4.5:1 AA test for normal text. APCA gives Lc 71.6, below the Lc 75 minimum the APCA authors suggest for body text columns at 16px/500 or larger sizes. Next, #888888 on white: WCAG 3.54:1 fails 4.5:1, while APCA gives Lc 63.1, above the Lc 60 level for non-body content text. Same colors, different verdicts, because the formulas weigh lightness differently. Press Swap colors to see light-on-dark polarity (negative Lc).
Formula notes
APCA (version 0.0.98G-4g). Luminance Y = 0.2126729·R + 0.7151522·G + 0.0721750·B, with each channel as (value/255)2.4. A channel Y at or below 0.022 is soft-clamped by adding (0.022 − Y)1.414. If the Y values differ by less than 0.0005, Lc is 0. For dark text on a lighter background: (bgY0.56 − txtY0.57) × 1.14; for light text on a darker background: (bgY0.65 − txtY0.62) × 1.14. A result under 0.1 in magnitude becomes 0; otherwise 0.027 is subtracted (or added for negative values), and the value is multiplied by 100. Source: apca-w3 (Andrew Somers, W3 licence); overview: APCA in a Nutshell. This tool’s output was checked against that reference code for nine color pairs.
WCAG 2.2. Relative luminance L = 0.2126·R + 0.7152·G + 0.0722·B with each channel linearised (c/12.92 at or below 0.04045, else ((c+0.055)/1.055)2.4), and ratio = (L1 + 0.05) / (L2 + 0.05) with L1 the lighter. Thresholds: 4.5:1 normal text and 3:1 large text at AA (SC 1.4.3), 7:1 and 4.5:1 at AAA (SC 1.4.6), 3:1 for UI components and graphics (SC 1.4.11). Source: WCAG 2.2, W3C Recommendation. Large text means at least 18pt, or 14pt bold.
Lc levels. Lc 90 preferred for fluent body text; 75 minimum for body columns; 60 for other content text; 45 for large, heavy text; 30 absolute minimum for other text; 15 for non-semantic non-text. Each level has size and weight conditions (shown in the table above) based on a Helvetica reference font. These are the APCA authors’ guidance as published at the Nutshell page, and as of 30 September 2026 APCA remains a draft, not a W3C Recommendation.
Limits. Hex colors only, opaque, in sRGB; no alpha blending, gradients or images. Font size and weight are not input here, so this tool shows each Lc level separately instead of a single pass/fail.
FAQ
Is APCA part of WCAG?
No. WCAG 2.2 uses the contrast ratio. APCA was developed for a future WCAG 3 draft and is not a WCAG 2 conformance method, so passing Lc does not satisfy SC 1.4.3, and failing it does not fail SC 1.4.3.
Why is Lc negative?
Negative Lc means light text on a darker background. The sign carries polarity, which the WCAG ratio ignores. Compare the absolute value against the levels.
Why does swapping the colors change Lc but not the ratio?
APCA models text and background differently, so black-on-white is Lc 106 while white-on-black is Lc −108. The WCAG ratio is symmetrical (21:1 both ways).
Which should I use?
If you need to show WCAG 2.x conformance, use the ratio. Lc is a useful second opinion, especially for dark mode and thin or small text.
Is this the same as the WCAG contrast checker on this site?
No. The Contrast Checker covers WCAG 2.x ratio tests only. This page adds APCA Lc.