Contrast tools

#ffffff
|
rgb(255, 255, 255)
Contrast value

-83.43 Lc

#6e45e4
|
rgb(110, 69, 228)
Sample text
Share these colors

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
100200300400500600700800900
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
            70
            55
            43
            40
            38
            35
            35
            35
            48px
            60
            50
            40
            38
            35
            33
            33
            33
            60px
            55
            45
            38
            35
            33
            30
            30
            30
            72px
            50
            40
            35
            33
            30
            30
            30
            30
            96px
            45
            35
            33
            30
            30
            30
            30
            30

            Table key

            • N
              WCAG 3.0 Rating 4 - meets or exceeds the values on the APCA Lookup table
            • N
              Rating 3 - 1-4% below
            • N
              Rating 2 - 5-9% below
            • N
              Rating 1 - 10-15% below
            • N
                Rating 0 - >15% below
              • NP
                Preferred for blocks of text
              • N+
                Add 15 Lc to use for blocks of text
              • Font weight 100 should be avoided
              • X
                Prohibited except for decorative purposes
              • Use for copyright/by-line only

              Example font combinations & ratings

              14px/400
              Rating: 0
              16px/400
              Rating: 2
              16px/600
              Rating: 4
              24px/500
              Rating: 4
              30px/300
              Rating: 4

              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.

              #ffffff
              |
              rgb(255, 255, 255)
              Contrast value

              5.78:1

              #6e45e4
              |
              rgb(110, 69, 228)
              Sample text
              Share these colors

              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