This is one of those apps that make you exclaim, “why didn’t I think of that?” Developer DBT has created a little app that solves a big problem. Bolt Sizer uses your Android phone’s camera, a coin and a little mathematical magic to instantly tell you the size of the bolt in the photo. This is the perfect app for anybody working with carpentry or other household tools, and occasionally just about everybody else.

It works like this: start up the app and tap settings. Select any coin that happens to be in your pocket or change drawer. The app works with an American penny, nickel, dime or quarter, or a Euro 1, 5, 20, 20 or 50 cent piece. Point your camera towards your table or desk, take a photo, adjust the circle around your coin, and the app will use it as a physical reference to measure the bolt. You can get both the length of the shaft and the head size, in Imperial or Metric.

If you’d like to use the app for free or just need it periodically, there’s a free ad-supported version. If you plan on using it regularly, be a good Android citizen and shell out 99 cents for the ad-free version. There’s no functional difference between the two. The developer plans to add even more options in the future, so keeping it on your phone might be a god idea. Great idea, dev – keep ’em coming.

[via Reddit]