To find out how readable your writing is, check out this online tool: Readability Tester. It evaluates your writing using three measures, and very helpfully explains what they mean.
For example, here’s what I obtained when I put a recent article of mine through it:
Your score is 57.7
That's pretty good. Your grade is about nine, which is at the same reading level as the BBC News website.
And if you're wanting a little more detail your Gunning FOG score is 11, and your SMOG score is 8.6
This means that the reading age of the article is about 15.
What is also very useful is the comparison table it provides at the end of the process. In this case, it told me that my article was harder to read than President Obama’s speeches, but less difficult than the Financial Times:
This is definitely a very good tool to have at your disposal — and it’s free. Run your article through the Readability Tester before sending it off to the editor.
See also: Make it readable.