The rules that ask for contrast.

Four instruments, one requirement. Each points at the same standard, WCAG, and at the same level within it, AA. They differ in who they cover and in what happens when you fail.

European Accessibility Act

European Union

Applies to: Anything sold online to EU consumers.
Requires: WCAG level AA
Applies from: 28 June 2025
If you fail: Penalties reach six figures.
In full: Enforcement is national, so the penalty depends on the member state, and in several it reaches six figures. The technical benchmark is EN 301 549, which points at WCAG level AA. It covers e-commerce, banking, transport and e-books, and it applies wherever the seller is based as long as the customer is in the EU.

ADA Title III

United States

Applies to: Private businesses open to the public.
Requires: WCAG level AA
Applies from: Today
If you fail: Lawsuits. $4,000 per violation in California.
In full: No web rule was ever published for Title III, so there is nothing to comply with in advance. Courts and settlements use WCAG level AA anyway, and in California the Unruh Act adds statutory damages of $4,000 per violation on top.

ADA Title II

United States

Applies to: Government, and who it buys from.
Requires: WCAG 2.1 level AA
Applies from: 26 April 2027
If you fail: DOJ complaints and private lawsuits.
In full: The Department of Justice rule names the version and the level outright, which removes the usual argument that no standard was specified. Entities serving 50,000 people or more have until 26 April 2027, smaller entities and special districts until 26 April 2028.

Section 508

United States

Applies to: Anything sold to a federal agency.
Requires: WCAG 2.0 level AA
Applies from: Today
If you fail: Excluded from the contract.
In full: It is a procurement condition rather than a complaint process, so it is settled before the contract is signed rather than after somebody objects. The referenced level is WCAG 2.0 AA.

What the measurement is called

The number is a contrast ratio: how far a text color sits from the color behind it, on a scale from 1:1 to 21:1. Identical colors give 1:1. Black on white gives 21:1.

Level AA asks for 4.5:1 on normal text, and 3:1 on text at 24px or larger and on interface parts like buttons and inputs. Level AAA asks for 7:1 and no regulation requires it.

There is no partial credit. A color below its threshold is a failure whether it misses by two points or by 0.02, and the ones that miss by a hair are the ones nobody sees.

Contrast is one requirement among many in WCAG. This is a contrast report, not a certificate of compliance. It is the part of the standard that is arithmetic, which is why it is the part that can be settled exactly.