Question 1

What contrast ratio passes WCAG AA?

Accepted Answer

WCAG 2.1/2.2 Level AA requires a contrast ratio of at least 4.5:1 for normal text and 3:1 for large text (SC 1.4.3). User-interface components and graphical objects need at least 3:1 (SC 1.4.11).

Question 2

What contrast ratio is needed for AAA?

Accepted Answer

Level AAA (SC 1.4.6) requires 7:1 for normal text and 4.5:1 for large text. There is no AAA level defined for non-text (UI) contrast.

Question 3

What counts as large text in WCAG?

Accepted Answer

Large text is at least 18pt (about 24px) for regular weight, or at least 14pt (about 18.66px) when bold. Large text has a lower contrast requirement than normal text.

Question 4

How is the contrast ratio calculated?

Accepted Answer

Each sRGB channel is linearized (c/12.92 if c is at or below 0.03928, else ((c+0.055)/1.055)^2.4), combined into relative luminance L = 0.2126R + 0.7152G + 0.0722B, then the ratio is (L1 + 0.05) / (L2 + 0.05) with L1 the lighter color.

Question 5

What is the maximum possible contrast ratio?

Accepted Answer

The maximum is 21:1, achieved by pure black (#000000) on pure white (#ffffff). The minimum is 1:1 when both colors are identical.

Question 6

Does this checker use APCA (WCAG 3)?

Accepted Answer

No. This tool uses the established WCAG 2.x contrast-ratio algorithm. APCA is part of the WCAG 3 draft and is not yet a recommendation, so it is not used here.

적용 대상	AA	AAA
일반 텍스트 18pt(약 24px) 미만 · 14pt bold 미만	✓ 통과	✓ 통과
대형 텍스트 18pt(약 24px) 이상 · 14pt bold 이상	✓ 통과	✓ 통과
UI 요소·그래픽 버튼 경계·아이콘·차트 등 (SC 1.4.11)	✓ 통과	해당 없음

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