Calculating Tile for a Small Bathroom
Worked scenarios are illustrative composites. Our editorial pen name and method.
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A small bathroom looks like the easiest tile job in the house — “it’s a 5-by-8, that’s 40 square feet, done.” It isn’t, quite, for a reason that trips up even careful DIYers: the tiled field is rarely the whole footprint, and what you subtract depends on a detail you have to decide before you measure — whether the tub, vanity and toilet sit on top of the finished floor or under it. Small rooms also punish waste harder, because a single bad cut is a bigger fraction of a small order.
The footprint is the starting point, not the answer
A nominal 5-by-8 bathroom is a 40 sq ft gross footprint. What actually gets tiled depends on the assembly:
- A tub or shower base usually sits on the subfloor, so you tile up to it, not under it — subtract its footprint.
- A vanity may be installed over the tile or set on the subfloor first — that choice changes whether you tile beneath it.
- The toilet flange sits in the floor; you tile around it and set the toilet on top.
So sketch the room, split it into rectangles, and subtract only the footprints the approved assembly won’t cover. Add any niche, closet or connected area that will be tiled. Don’t subtract movable items, and don’t apply a blanket rule that “every tub, vanity and toilet is handled the same way” — they aren’t.
For each rectangle:
Area = length × width
Sum the tiled rectangles. Curves, flange cuts, thresholds and irregular walls influence how much you’ll cut even when they don’t change the measured field.
Add a layout-specific overage
Tile size, pattern, batch, room edges, breakage, minimum usable cut and your installer’s plan all affect the order — a straight layout isn’t automatically 10%, and a small bathroom isn’t automatically 15%. Small rooms have a quirk worth knowing: they have a high ratio of edges to field, so cuts along the walls make up a bigger share of the job, and a large-format tile in a tiny room can waste more than a small mosaic would.
Target tile = measured tiled area × (1 + overage ÷ 100)
Cartons = target tile ÷ carton coverage, rounded up
Because the order is small, one extra carton is a big percentage jump — run a couple of overage cases and keep any intentional repair stock as its own line, not baked into the overage.
A real safety stop for older bathrooms
Before you demo an old floor to see what’s under it: stop if the existing floor or its adhesive might contain asbestos. Older sheet vinyl, floor tiles and the black “cutback” adhesive under them can, and you can’t identify it by looking. The EPA explains that suspect materials may need professional sampling and that intact material is often best left undisturbed:
Don’t sand, scrape or dry-cut a suspect old floor just to plan a new one.
The finish material is only part of the assembly
The carton count covers the tile itself. A tiled bathroom floor is a system — substrate, waterproofing membrane, mortar and grout — and each of those is a separate product with its own coverage and its own instructions. Use the tile, mortar, membrane and grout manufacturers’ guidance to design the assembly; this page only sizes the finish-tile purchase after that design is set.
Bathroom tile takeoff errors
- Tiling the whole footprint on paper. Subtract what the assembly won’t cover; add niches and closets.
- Assuming fixtures are all handled the same. On-top-of vs under-the-floor changes the field.
- Using a room-style overage. Small rooms have more edge cuts; run a couple of cases.
- Disturbing a suspect old floor to investigate. Test for asbestos; don’t scrape to find out.
Finish quantity is not an assembly design
This sizes the finish tile after the assembly is decided; it doesn’t design the waterproofing, substrate or fixture sequence, and it can’t identify hazardous old materials. Follow the tile, membrane, mortar and grout instructions, and treat any suspect existing floor as a job for testing, not guesswork.
Enter your measured tiled field and a layout-specific overage in the flooring calculator; the pattern buttons only seed a default, and the percentage stays editable. These are general-information estimates, not professional advice.