What’s the difference between web accessibility and usability?

I was recently asked to explain the difference between web accessibility and usability. I struggled to come up with a clear answer, so took some time to research how others had answered the question. While there are some good explanations out there, there wasn’t one I was happy forwarding to the questioner.

Taking bits from a few sources and adding my take, here’s how I replied:

Web accessibility and usability are closely linked, it’s no surprise you could do with some help defining the two concepts. I wasn’t sure at first if I could do it justice, but I’m pleased with what I have written – hope it helps.

Web accessibility

Web accessibility is what I deal in, so let’s start there. It’s all about helping people with disabilities have an equivalent experience to everyone else when browsing the web. I’ve avoided saying “the same experience” as users with disabilities often see, hear or feel the world differently. To me “equivalent” means that they get the same information, options and enjoyment – it may just be presented differently.  

Things like the Web Content Accessibility Guidelines aim to make the web more accessible to people with disabilities.

Accessible websites benefit people with disabilities in particular.

Usability

Usability, on the other hand, is more to do with designing a user-friendly approach. It’s concerned with how people interact with a website’s interface – is it easy to do the things people want to do? Can people quickly find what they want without help? Do people make lots of mistakes using a website? Do people enjoy using the website?

Usable websites benefit everyone.

In summary

A useful way to think about the distinction is this:

A website must be accessible to be usable, but it doesn’t need to be usable to be accessible.