Colour contrast calculator: easily check WCAG-compliant colours

A colour contrast calculator is a digital tool that helps you to ensure the legibility of text and graphic elements on websites, in apps or other digital products. It calculates the contrast ratio between two colours - typically a foreground colour (e.g. text colour) and a background colour - and checks whether this ratio meets the requirements of the Web Content Accessibility Guidelines (WCAG).

You may be wondering why so much importance is attached to colour contrast. Sufficient contrast between foreground and background colours is fundamental to making digital content accessible to all user groups. People with various types of visual impairments, such as colour blindness, generally low vision or age-related visual impairments, benefit enormously from well-contrasting colours. For them, too little contrast can mean that texts are difficult or impossible to read and important information is lost.

However, the benefits of good colour contrast are not limited to people with visual impairments. Every user benefits because a clear distinction between text and background improves general legibility and reduces eye strain. Just think of situations where you are trying to read content on your smartphone in bright sunlight or need to quickly grasp information on a small screen. In all these moments, a strong contrast makes all the difference for a positive user experience (UX). In addition, compliance with accessibility standards, as required in Germany by the Barrier-free Information Technology Ordinance (BITV) based on the WCAG, is not just a recommendation in many areas, but a legal obligation.

Fortunately, most colour contrast calculators are very straightforward and user-friendly. As a rule, you enter the colour codes of the foreground and background colour to be checked in the fields provided. Hexadecimal codes are the most common (e.g. #333333 for a dark grey or #FFFFFF for white), but many tools also accept RGB (red, green, blue) or HSL (hue, saturation, lightness) values.

Once you have entered the colours, the tool calculates the exact contrast ratio in the background. This calculation is based on the relative luminance values of the two colours, a measure of how bright a colour appears to the human eye. The result of this calculation is a number, for example 7.5:1. The calculator then shows you whether this ratio fulfils the minimum requirements of the WCAG for different conformance levels (usually AA and AAA) and for different text sizes (normal text vs. large text). Many modern contrast calculators also offer a direct visual preview of the selected colour combination so that you can get an immediate impression of the effect.

To make the application clearer to you, we would like to introduce you to a recommended and easily accessible tool: the contrast calculator for colours from barrierefreies.design. This online tool is characterised by its intuitive operation and clear presentation of results. You can define your foreground and background colours using hex, RGB or HSL values. The tool immediately provides you with the exact contrast ratio and an easy-to-understand evaluation in accordance with the WCAG 2.1 criteria for levels AA and AAA, for both normal and large font sizes. The additional visual preview helps you to assess the colour effect directly. This calculator is an excellent example of how you can easily check and optimise the accessibility of your colour decisions.

Using a colour contrast calculator should not be a one-off act, but an integral part of your design and development process. Start checking the colour contrasts as early as possible, ideally during the first design drafts, to avoid costly corrections later on. Don't just think about the body text of your website or app, but also consider all interactive and informative elements. This includes buttons, links, icons, form fields and their labelling as well as graphic elements that convey important information.

Many modern web browsers now have integrated developer tools that also offer contrast checking functions and are a good addition to specialised calculators. And perhaps the most important piece of advice: never rely solely on your subjective perception. A colour combination that appears clear and distinct to you personally may be illegible to another person with a visual impairment. The objective figures and assessments of a contrast calculator are your most reliable guide here.

By using colour contrast calculators regularly and consciously, you are making an important contribution to digital inclusion. It's a seemingly small tool, but it has a hugely positive impact on the accessibility and user-friendliness of your digital products for all people.