This app was mentioned in 7 comments, with an average of 2.29 upvotes
There already is an application for that. It's fairly reliable. It's called FittingRoom by Asphaltgold Sneakerstore. I've really only encountered this with Adidas shoes. They're horribly inconsistent. If I absolutely cannot get a consistent answer I'll go half size up. Worst case scenario I have to lace it slightly tighter. I'd never, ever go down unless I know 100% that it's a good idea.
https://play.google.com/store/apps/details?id=de.asphaltgold.app
Try this app, it has really helped me with sizing.
https://play.google.com/store/apps/details?id=de.asphaltgold.app&hl=en
or
https://itunes.apple.com/de/app/asphaltgold-fittingroom/id943110749?mt=8
Pentru incaltaminte folosesc aplicatia asta: https://play.google.com/store/apps/details?id=de.asphaltgold.app&hl=en
If you're having problems with sizing check this app out https://play.google.com/store/apps/details?id=de.asphaltgold.app
I'd go a half size down.
You should check out the app asphaltgold fittingroom if you ever wonder how shoes fit.