If you using YOAST plugin, you will see at the bottom of the page "readability". Readability is referred to the content framing. it is usually the use of simple and easy words that makes your readers read your article easy. Personally, you cannot understand your own content readability because everyone has its own style of writing. the only way to calculate is using YOAST plugin that calculates your content readability with its own language and gives you result in form of "Score"