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Color contrast checker (WCAG 2.2)

Check the WCAG 2.2 contrast ratio between a text color and its background, with AA and AAA pass or fail for normal text, large text and UI parts.

Updated Checked against 5 worked examples

#RRGGBB, a CSS name, rgb(), hsl() or oklch().
Try
Contrast ratio
:1
Contrast ratio: 14.67 :1
Shown to 2 decimal places, truncate
AA normal text (≥ 4.5:1)
Pass
AA large text (≥ 3:1)
Pass
AAA normal text (≥ 7:1)
Pass
AAA large text (≥ 4.5:1)
Pass
UI components (≥ 3:1)
Pass
Text luminance
0.0215
Background luminance
1.0000

#1F2937 on #FFFFFF has a contrast ratio of 14.67:1, which passes AA normal text, AA large text, AAA normal text, AAA large text and UI components.

#1F2937 text on #FFFFFF

Normal text, 16 px: the quick brown fox jumps over the lazy dog

Large text, 24 px (18 pt): the quick brown fox jumps over the lazy dog

Large bold text, 19 px (14 pt): the quick brown fox jumps over the lazy dog

Where the ratio falls

FailLargeAAAAA134.572114.67:1
How it's calculated S

  1. Linearise each channel

    Clin={C/12.92C≤0.04045((C+0.055)/1.055)2.4otherwisetext (R,G,B)lin=(0.0137,0.0222,0.0382)\begin{aligned} C_{lin} &= \begin{cases} C/12.92 & C \le 0.04045 \\ ((C + 0.055)/1.055)^{2.4} & \text{otherwise}\end{cases} \\ \text{text } (R, G, B)_{lin} &= (0.0137, 0.0222, 0.0382) \end{aligned}

    WCAG's text prints 0.03928 as the threshold, the older sRGB draft value; for 8-bit colors both thresholds give identical results because no 8-bit value falls between them.

  2. Relative luminance

    Ltext=0.02153,Lbackground=1.00000L_{text} = 0.02153,\quad L_{background} = 1.00000

  3. Contrast ratio (lighter over darker)

    1.00000+0.050.02153+0.05=14.6791\frac{1.00000 + 0.05}{0.02153 + 0.05} = 14.6791

    Compared with the thresholds unrounded: 4.5 for normal text at AA, 3 for large text and UI parts, 7 and 4.5 at AAA.

About the color contrast checker

WCAG measures contrast as (L1 + 0.05) ÷ (L2 + 0.05), where L1 and L2 are the relative luminances of the lighter and darker color. Each luminance comes from the linearized sRGB channels, weighted 0.2126 for red, 0.7152 for green and 0.0722 for blue, so the ratio runs from 1:1 for identical colors to 21:1 for black on white.

Designers and developers check it before shipping text, buttons and icons. The default, #1F2937 slate text on a white background, measures 14.67:1 and passes all five checks, while #777777 on white measures 4.48:1, just under the 4.5:1 that AA needs for normal text.

The ratio is truncated to two decimals and compared unrounded, as WCAG requires, so 4.499:1 fails the 4.5:1 threshold. Alpha is ignored; blend a semi-transparent color onto its background first.

Worked examples

Black on white is the maximum

Text color
#000000
Background color
#FFFFFF
Contrast ratio
21.00 :1
AA normal text (≥ 4.5:1)
Pass
AAA normal text (≥ 7:1)
Pass

Checked against: WCAG 2.2 definition: (1 + 0.05) / (0 + 0.05) = 21

#777777 on white just misses AA

Text color
#777777
Background color
#FFFFFF
Contrast ratio
4.48 :1
AA normal text (≥ 4.5:1)
Fail
AA large text (≥ 3:1)
Pass
UI components (≥ 3:1)
Pass

Checked against: Python 3.8 decimal: luminance of 0x77 = 0.18447…, (1.05) / (0.23447…) = 4.4781…

#767676 on white passes AA

Text color
#767676
Background color
#FFFFFF
Contrast ratio
4.54 :1
AA normal text (≥ 4.5:1)
Pass
AAA normal text (≥ 7:1)
Fail
AAA large text (≥ 4.5:1)
Pass

Checked against: Python 3.8 decimal: 1.05 / (0.18116… + 0.05) = 4.5422…

Same color on itself (edge)

Text color
teal
Background color
#008080
Contrast ratio
1.00 :1
AA large text (≥ 3:1)
Fail
UI components (≥ 3:1)
Fail

Checked against: WCAG 2.2 definition: (L + 0.05) / (L + 0.05) = 1

Questions

What contrast ratio does WCAG require?

Level AA needs at least 4.5:1 for normal text and 3:1 for large text (success criterion 1.4.3), and 3:1 for user interface components and meaningful graphics (1.4.11). Level AAA raises text to 7:1 and large text to 4.5:1 (1.4.6). Logos, disabled controls and purely decorative text have no requirement. Most laws and procurement rules point to level AA.

What counts as large text in WCAG?

Large text is at least 18 point, or 14 point when bold. In CSS, where 1 pt is 1.333 px, that is 24 px for regular weight and about 18.66 px for bold. W3C's Understanding document puts these at roughly 1.5 em and 1.2 em of default body text, and warns that very thin fonts may need more. Large text only needs 3:1 at AA instead of 4.5:1.

What is the lightest gray text that passes AA on white?

#767676, which gives 4.54:1 on #FFFFFF. One step lighter, #777777, gives 4.48:1 and fails, because WCAG compares the exact ratio with 4.5 and allows no rounding up. For large text you can go much lighter: any gray that reaches 3:1, such as #949494 at 3.03:1, passes AA.

Did WCAG 2.2 change the contrast requirements?

No. WCAG 2.2 became a W3C Recommendation on 5 October 2023 and added 9 success criteria, mainly on focus visibility, target size and authentication, but the contrast criteria 1.4.3, 1.4.6 and 1.4.11 are the same as in WCAG 2.1. A color pair that passed under 2.1 still passes under 2.2, at the same 4.5:1 and 3:1 thresholds.

Does the order of text and background colors matter?

No. The formula always puts the lighter color's luminance on top, so white text on #1F2937 and #1F2937 text on white both measure 14.67:1. What changes is how the pair reads: light text on a dark background can look thinner or bolder depending on the font and screen, so check the actual rendering too, especially at small sizes.

How accurate is the color contrast checker?

Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 5 worked examples whose answers come from independent sources; for example, “Black on white is the maximum” is checked against WCAG 2.2 definition: (1 + 0.05) / (0 + 0.05) = 21.

Where does the method come from?

W3C WCAG 2.2 — Success Criteria 1.4.3, 1.4.6 and 1.4.11; definitions of contrast ratio and relative luminance; W3C Understanding SC 1.4.3 — large text is at least 18 pt, or 14 pt bold.

About this calculator

ratio=L1+0.05L2+0.05L=0.2126Rlin+0.7152Glin+0.0722Blin\begin{aligned} \text{ratio} &= \frac{L_1 + 0.05}{L_2 + 0.05} \\[4pt] L &= 0.2126 R_{lin} + 0.7152 G_{lin} \\ &\quad + 0.0722 B_{lin} \end{aligned}

Sources

  1. W3C WCAG 2.2 — Success Criteria 1.4.3, 1.4.6 and 1.4.11; definitions of contrast ratio and relative luminance
  2. W3C Understanding SC 1.4.3 — large text is at least 18 pt, or 14 pt bold

Checked against references

5 worked examples with independently sourced answers ship with this calculator. They run in the test suite; you can run them here too.

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