It’s supposed to be a simple way to replace a worn-out floor. And it’s true: You can install peel-and-stick vinyl tiles with just a few tools (a straightedge, a sharp utility knife.) But simple it’s not: There’s math involved.

Need to know: The exact square footage of the room you’re tiling. That involves measuring the width and length of the room right to the wall, not just to the shoe molding or baseboard. If you don’t measure to the walls, you may find yourself with less tile than you need.

While you’re at it, find the center of the floor you are covering: Measure each of the four walls to find their midpoints, then draw two lines across the floor from those points; where the lines intersect is the center of the room. Start putting down the tiles there and work your way out. That way, if you need to trim a tile to fit, the cut is hidden under the baseboard or the molding, and the irregular-size tile isn’t in the middle of the room.

Be sure to ask: Whether vinyl tile is right for the room. It may be the wrong choice for a mudroom, for example, because dirt gets ground into the surface. Ceramic or laminate floors are easier to keep clean.

What it will cost: For larger jobs, it’s cheaper to buy by the box, rather than individual tiles. The average price of a 12-inch-by-12-inch self-adhesive vinyl tile is about $1, but style and quality can push the cost up. Go cheap and you’ll be putting in a new floor in a year.

Good advice: Always buy more than you think you’ll need. The experts say 5 percent more, because of the trimming that needs to be done at the edges. And since styles change frequently, get an extra box or two, in case you need to replace part of the floor. Remember to keep your work space ventilated; the adhesive on the back of the tile may be toxic.

Bad advice: “Just sand the existing floor to make it flat.” Floor tiles in older houses often contain asbestos fibers that can be released into the air if they are disturbed. If you suspect this is the case, you’ll have to install a subfloor; typically a half-inch of exterior plywood is the easiest. This means, however, that door bottoms will need to be trimmed so they open properly; you may have to accommodate appliances as well.