It checks your photo against scientific standards for beauty - like facial symmetry and how wide the mouth is compared to the eyes. Then, it gives you a number between one and 100.
Jo Overline, the app's creator, says it's selling like crazy and is all in fun, but some people aren't laughing.
"Last month we were number one in China for about three weeks. We were the number one app overall. It doesn't matter. Everybody is interested in vanity and they like to know where they rank," he said.
More than 5 million people have bought the Ugly Meter app.