How to Find the Center of the Floor to Lay Tile

When you lay tile, you should start in the center of the floor rather than along a wall. This ensures the grout lines line up with the sight lines in the room. It makes the room feel symmetric, calming and inviting instead of incongruent and discordant.

To follow this approach, you have to find the center of the room, and while that sounds easy, it's a little more complicated than you might think. The problem is that most rooms aren't square, and if you assume a room is square when it isn't, the center point you measure will be different than the actual one. You need to use the same procedure you'd use for squaring a floor for hardwood flooring.

It would be nice if there were a center-of-room calculator you could buy, but there isn't, so you have to use old-fashioned tools. These include a tape measure, a chalk line and a little math. The easiest way to check if a rectangular room is square is to measure both diagonals (from corner to corner in two different directions) with a tape measure. If they aren't the same, the room isn't square.

Now, measure the lengths of pairs of opposing walls. If one wall is longer than the other, the perpendicular walls aren't square. Here's how to square them:

1. Subtract the length of the shorter wall from that of the longer one. The difference is the amount the perpendicular walls are angled to each other.
2. Make a mark half this difference from the corner of each perpendicular wall on the end that adjoins the corner of the longer of the two walls you measured.
3. Snap a chalk line from each mark to the opposite corner.

The chalk lines make the room square, and if you use them to find the center of the floor, the center you find will be the true center. Of course, you'll have to fill the gaps between the chalk lines with angled pieces of tile, but you'd have had to fill gaps anyway.

Now that you've squared the room, double check by measuring the distance between diagonals, using the chalk lines as references instead of the actual walls. If the distances are the same, you can follow the standard procedure to find the center of the floor.

Find the mid-point of each chalk line or wall (if the walls are straight). Use a carpenter's square to draw a perpendicular line toward the other wall, then join these lines with a chalk line.

The intersection of the chalk lines would be the midpoint of the room if it were square, and it's the place to begin to lay tile. The corners of the first four tiles you lay should meet at this point.

Some rooms have one or more curved walls, some have alcoves and some are L-shaped. Whenever possible, you want to create the largest single rectangle you can, ignoring for the moment parts of the floor that aren't in this rectangle. This strategy works for most rooms except triangular ones.

If a wall has a concave curve with respect to the rest of the room, snap a straight line between the ends of the curved wall and use that line to find the center of the floor. In L-shaped rooms, use the larger part of the L as your primary rectangle.

To find the center of a triangular floor, treat the longest wall as the base of the triangle. Find the center and draw a line from that point to the apex of the triangle. Find the midpoint of the line and start laying tile from that floor point.