What Is a Website Authority Score — and Why Does Semrush Say 6 While Ahrefs Says 20?

If you've spent any time in SEO tools, you've run into some version of an authority score. Semrush has one. Ahrefs has one. Moz has Domain Authority. They all claim to measure roughly the same thing — and they almost never agree with each other. Right now Ritner Digital's Semrush Authority Score is 6. Pull up the same domain in Ahrefs and it comes back at 20. Same domain, same day, fourteen points apart. Here's exactly why that gap exists and what either number actually means for your rankings.