What is Domain Authority and how do I check it?

Domain Authority (DA) is a metric used to evaluate sites based on how well they are likely to rank in search engines. It has become a replacement for Google PageRank, which was widely used in the early 2000s for this purpose, but is no longer published. 

Domain Authority is was developed by Moz, and the best way to find out your site's DA is to head over to Moz.com's Link Explorer tool: https://moz.com/link-explorer. You'll have to sign up for a free Moz account to use this service.

The tool will analyse the site that you entered and provide a numeric score. You can also use the tool to compare the results for different sites. 

If you select "exact page" rather than "root domain" the tool will give you a couple of numbers: Domain Authority, which measures the rank of the site as a whole, and Page Authority (PA), which measures the rank of a particular page -- this will probably be your homepage in your first test. You can also measure the PA of particular posts or pages by pasting the URL for that page in the search bar.

Scores range from 1 to 100, but since this tool is comparative, there's no "good" or "bad" score. Very well-regarded sites like Wikipedia or the New York Times will have high scores, and brand-new sites always start with a score of 1. 

If you are curious about how your site's Domain Authority (DA) measures up, it can be helpful to use Link Explorer to analyse a handful of similar sites and benchmark your DA score against those. However, be aware that the free version of Link Explorer only allows you ten tests per month, so choose your comparison sites carefully, and run the test for your site first. 

How do I improve my Domain Authority?

Good question! Domain Authority is influenced by a variety of factors, so there's no clear route to improvement. As a general rule, though, a good way to improve Domain Authority is by improving its link profile -- the more high-quality sites that link to your site, the better. Also, be aware that Domain Authority scores are only updated every 2-3 months, so any changes you make to the site will not be immediately reflected in your Domain Authority score.
Check out  Moz's article about Page Authority for more advice on this topic.