Contrast tools
-83.43 Lc
APCA and WCAG 3.0
The Advanced Perception of Color Algorithm (APCA) considers the context in which colors are used to determine their readability. Font size, font weight, and the sequence of background and text colors all impact the recommended contrast value (Lc) for text.
APCA was included in previous working drafts of the WCAG 3.0 text contrast guidelines . However, the W3C Editor's Draft of WCAG 3.0 from June 2nd, 2023 reverted all guidelines to "Placeholder" status and removed prior guideline content, including text contrast and APCA.
The proposed WCAG 3.0 ratings for text contrast were based on the proximity of a calculated contrast value to its target score on the APCA Lookup Table below.
Although APCA’s eventual role in WCAG 3.0 is unclear, the APCA Readability Criterion (ARC) is developing as an independent standard for visual contrast. You can learn more in the ARC public working draft .
APCA Lookup Table
Font weight | |||||||||
---|---|---|---|---|---|---|---|---|---|
100 | 200 | 300 | 400 | 500 | 600 | 700 | 800 | 900 | |
12px | X | X | X | © | © | © | © | X | X |
14px | X | X | © | 100P | 100P | 90P | 75P | X | X |
15px | X | X | © | 100P | 90P | 75P | 70+ | X | X |
16px | X | X | © | 90P | 75P | 70+ | 60+ | 60 | X |
18px | X | © | 100P | 75P | 70+ | 60+ | 55+ | 55 | 55 |
21px | X | © | 90P | 70P | 60+ | 55+ | 50+ | 50 | 50 |
24px | X | © | 75P | 60+ | 55+ | 50+ | 45+ | 45 | 45 |
28px | X | 100 | 70+ | 55+ | 50+ | 45+ | 43+ | 43 | 43 |
32px | X | 90 | 65+ | 50+ | 45+ | 43+ | 40+ | 40 | 40 |
36px | X | 75 | 60+ | 45+ | 43+ | 40+ | 38+ | 38 | 38 |
42px | 100 | 70 | 55 | 43 | 40 | 38 | 35 | 35 | 35 |
48px | 90 | 60 | 50 | 40 | 38 | 35 | 33 | 33 | 33 |
60px | 75 | 55 | 45 | 38 | 35 | 33 | 30 | 30 | 30 |
72px | 60 | 50 | 40 | 35 | 33 | 30 | 30 | 30 | 30 |
96px | 50 | 45 | 35 | 33 | 30 | 30 | 30 | 30 | 30 |
Table key
- WCAG 3.0 Rating 4 - meets or exceeds the values on the APCA Lookup table
- Rating 3 - 1-4% below
- Rating 2 - 5-9% below
- Rating 1 - 10-15% below
- Rating 0 - >15% below
- NPPreferred for blocks of text
- N+Add 15 Lc to use for blocks of text
- NFont weight 100 should be avoided
- XProhibited except for decorative purposes
- ©Use for copyright/by-line only
Example font combinations & ratings
Attributions
SAPC & APCA were invented / developed by Andrew Somers, Senior Color Science Researcher at Myndex Technologies as part of the ongoing PerceptEx™ Perception Research Project.
SAPC: S-LUV Advanced Perceptual Color — an appearance model for self-illuminated displays
APCA: Advanced Perceptual Contrast Algorithm — a method for determining contrast to guide web-based design.
APCA is derived from the SAPC model. APCA is a method for prediction pf suprathreshold visual contrast of text on displays. APCA results are intended to provide design guidance for best readability of web-based content.
APCA DISCLAIMER
APCA is intended solely for web-based content per the W3 WCAG 3.0 standards, and the web-content version is licensed to the W3 per their cooperative agreement. Use for other-than web-based-content is restricted and/or prohibited. APCA is a public beta, under active development. Prior written authorization is required for the use of SAPC or APCA in the context of, or in applications for, transportation, aerospace, medical, military, or where human safety is involved.
5.78:1
Normal text
- WCAG 2.1 AA
- pass
- WCAG 2.1 AAA
- fail
Large text
Text that is 14pt (18.67px) and bold or any text bigger than 18pt (24px) is defined as large scale text.
- WCAG 2.1 AA
- pass
- WCAG 2.1 AAA
- pass