From the Forums: How to Lay Tile Square with the Shape of the Room

Posted by: on November 16th, 2012 | One Comment
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A man lays tiles on a concrete floor


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. Something a bit more scholarly and mathematical.

In the picture above is the floor plan for a common bathroom. What I have done is found the center of the two opposing walls and marked them using the blue line that goes down the middle of each. This breaks the room into a smaller grid, and into four even sections … right?

Well … not always …

Even with the most accurate of tape measures, things can come out a bit off. Aside from going back and redoing all the measurements, there is a quick way to check if your center point is perfectly square.

In the picture above, you’ll notice the triangle that I’ve created. This is the basis for what’s known as the 3-4-5 Method.

  • Starting from the center point, measure down 3 feet on one line, and 4 feet on the other, making a mark at each point. If you’re really in a pinch for room, you can substitute the feet for cm or inches if you really need. But keep the numbers constant.
  • When you measure from mark to mark, you should see that it equals 5 feet (inches, cm, etc.). If it does, then you know you’ve created a square area! If not, then redo your chalk lines and try again.

Takes you back to high school math class, doesn’t it? Who would imagine we’d actually use all that information in real life!

Just a quick tip that I learned a while back from a tile pro that hopefully you all can find a use for in your home projects!

Check out our YouTube video how to lay tile in a bathroom for a video tutorial.

You can always find Jay on our How-To Community Forums answering questions and sharing tips about home improvement. Look for him posting under the handle Ask_Mr_Jay.

We have more advice and project ideas from our experts. Visit the Forums for DIY tips and and gardening advice from our store associates. From the Forums is our weekly column highlighting the best of The Home Depot’s Community Forums.

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  1. Andrew says:

    Note that the information above only assists in verifying that the intersecting lines drawn to mark off the segments of the room are approximately perpendicular to each other. It does not verify that the lines are properly centered along either axis of the room, or that they are even perpendicular to the walls of the room.