Published August 19, 2026 · Updated August 23, 2026 · By Tupep
Forty square feet, and why you cannot buy forty tiles
A 5 by 8 foot bathroom is 40 square feet of floor. A 12×12 tile covers exactly one square foot, so the temptation is to buy 40 tiles and add a couple for luck. Buy 48.
The math is not wrong. A bathroom floor just has four or five specific cuts that no square footage calculation knows about, and each has a real chance of eating two tiles instead of one. This is the plain baseline job. No diagonal, no large format, no pattern.
The formula
Field tiles = ceiling(width / module) x ceiling(length / module)
Order = field tiles x 1.10, plus a fixture allowance
The fixture allowance is the part that gets skipped. It is a flat count, not a percentage, because a toilet flange takes the same number of tiles whether the room is 40 square feet or 400.
The cut plan
Our room is 60 by 96 inches. With a standard 3/16 inch grout joint for a pressed, cushioned edge 12×12, the module is 12.1875 inches.
| Direction | Length | Module | Full tiles | Positions | Cut strip |
|---|---|---|---|---|---|
| Width (5 ft) | 60 in | 12.1875 in | 4 (48.75 in) | 5 rows | 11.25 in |
| Length (8 ft) | 96 in | 12.1875 in | 7 (85.31 in) | 8 columns | 10.69 in |
Five rows by eight columns is 40 tile positions. Both cut strips are over ten inches, which is a good sign. If either came out under about 3 inches we would shift the field half a tile so the leftover splits between the two opposite walls instead of leaving a sliver.
The fixture allowance
Here is what a 5×8 bathroom throws at you that a bedroom floor does not.
| Detail | Tiles involved | Extra to buy | Note |
|---|---|---|---|
| Toilet flange | 2 to 4 | 2 | Curved cuts crack, plan to redo one |
| Vanity or pedestal foot | 2 | 1 | Scribed curve, no straight reference |
| Supply line escutcheons | 1 to 2 | 1 | Notch from the back edge, not a hole |
| Doorway threshold | 1 | 0 | Runs under the door stop, plan the joint |
| Fixture allowance | 4 tiles | ||
So the full order: 40 positions x 1.10 for ordinary cut and breakage waste is 44, plus 4 for fixtures is 48 tiles.
Box rounding, which is where the real number lands
Tile is sold by the carton and cartons vary a lot in the 12×12 category. Work out both the tile count and the carton count before you go to the store.
| Carton size | Cartons needed | Tiles you get | Attic stock left |
|---|---|---|---|
| 11 sq ft (11 pcs) | 5 | 55 | 7 tiles |
| 15 sq ft (15 pcs) | 4 | 60 | 12 tiles |
| 16.7 sq ft (16 pcs) | 3 | 48 | 0 tiles |
That last row is a trap. Three cartons hits 48 exactly, which is zero margin. We always take one more carton and return it unopened. Ask about the return policy first, because plenty of places will not take back a special order.
The toilet flange, in detail
This is the cut that turns a one day bathroom into a two day bathroom. A closet flange is typically around 7 inches across at the outer ring. It usually lands so that two tiles meet at its centerline, occasionally four.
Cut it with a diamond hole saw sized to the flange body, then open the arc out with an angle grinder and a small diamond blade. Cutting the whole arc freehand is how tiles snap. Keep the tile wet and take light passes.
The flange should end up sitting on top of the finished tile, not buried under it, so the closet bolts and the seal have something to work against. If the flange ends up below the new surface it commonly gets brought up with a spacer ring kit and longer bolts. Rough in heights are code items in most jurisdictions, so confirm with your building department or your plumber.
The threshold, and where to start the layout
Start the layout from the doorway, not from the geometric center of the room. In a 5×8 bathroom, the only view anybody ever gets is standing in the door, and a full tile centered on the opening reads as intentional. Work outward from there and push the cut strips to the far wall and behind the toilet.
At the doorway itself, the tile should stop directly under the closed door slab so neither room sees the transition. If the bathroom tile finishes higher than the adjoining floor, that step gets a transition strip sized to the actual height difference, and you want to know that number before you set the last course.
Substrate and mortar specifics
- Backer. A quarter inch cement backer board bonded and fastened over a wood subfloor is a common approach for a small bathroom floor, as is an uncoupling membrane. Both are governed by the manufacturer’s written instructions and by local code, so verify before you commit.
- Flatness. Check with a 6 foot straightedge. For 12×12, 1/4 inch in 10 feet is the usual tolerance, and a 5×8 room rarely has a hump that big. Fix any that it does before you start.
- Trowel and coverage. A 1/4 x 3/8 square notch is standard for 12×12 and runs roughly 85 to 95 square feet per 50 pound bag. One bag covers this floor with room to spare, and you will still need a second bag if you also bond the backer board down, since that layer takes its own mortar.
- Joint width. Cushioned edge pressed tile has enough variation in facial size that a 1/16 inch joint will not close cleanly. Three sixteenths is the honest minimum for this tile, and 1/4 inch is common. Rectified tile is the only kind that belongs in a tight joint.
- Set the door casing first. Undercut the casing with a jamb saw using a scrap tile plus a scrap of mortar as your height gauge, so the tile slides under instead of getting scribed around it.
Related guides
- Tile for a Shower Surround: Walls, Floor, Niche
- Subway Tile Backsplash: How Many Square Feet for a Kitchen
- How Many 12×24 Tiles for a Standard Bathroom Floor
- Epoxy Grout Coverage vs Cement Grout
Sources and Further Reading
Run your own numbers with the Tile Calculator, or browse every tool on the calculators index. Coverage figures and material constants are cross-checked against manufacturer technical data sheets before publication. See our Methodology page for how figures are selected and verified.
Planning estimate only. Results assume standard conditions and are intended for material planning. Verify against your product’s technical data sheet and your local building code before purchasing. Structural, electrical, and gas work should be specified by a licensed professional.
Last updated: August 23, 2026
Leave a Reply