Installing tile on a bathroom floor can be a very gratifying do-it-yourself project, and it will cost a lot less than paying someone else to do it for you. It’s a fairly easy job, too, but getting it started right is crucial. You’ll want to create guide lines that are perfectly square, otherwise you could end up with what’s formally called a “wonky-looking floor.” Creating those perfectly square lines can be a little tricky.

Home Depot Forums associate Jay Harris has a handy way to use geometry and the insight of Pythagoras to get your tile layout straight and square. It involves an ancient mathematical principle. But don’t worry — there won’t be a quiz.  

Recently, I had a customer in the store who was a bit unsure about how he was laying out his tile. We’d worked together previously to pick out the tile itself, and I made sure to let him know to do a dry-layout first. He’d run into a bit of a snag when doing his chalk lines, though, as they didn’t quite look square.

Now sometimes you can measure these out with a square caliper or framing ruler, but I rely on a different approach.