A small bathroom floor is the tile job most people tackle first — small enough for a weekend, big enough to learn on. This guide prices retiling a 40 sq ft bathroom floor before you start: the exact tiles, boards, and bags to buy, and what they add up to at typical US prices.
The assumptions, up front. An 8 × 5 ft bathroom floor, retiling with 12 × 12 in ceramic floor tile, 1/8 in grout joints, and a standard 10% waste allowance. The old floor is already removed and the subfloor is sound — this estimate covers backer board, tile, and setting materials, not demolition. If your floor differs, the same math is built into the calculator further down this page.
How much tile a 40 sq ft floor needs
- Area: 8 × 5 = 40 sq ft.
- Tile coverage: each 12 × 12 in tile plus its share of the grout joint covers about 1.02 sq ft, so the floor takes about 39 tiles before waste.
- With 10% waste: 44 tiles.
- Boxes: at 10 tiles per box, 44 ÷ 10 rounds up to 5 boxes — which also leaves a few spares from the same dye lot if a tile ever cracks.
Materials list and cost
Typical US prices, checked November 2026 — the same figures used on our Tile Calculator page. Materials only.
| Item | Quantity | Typical cost |
|---|---|---|
| Ceramic floor tile, 12 × 12 in | 5 boxes of 10 (50 sq ft) | $75 – $250 ($1.50 – $5.00 per sq ft) |
| Cement backer board, 3 × 5 ft sheets | 3 sheets (45 sq ft) | $30 – $45 |
| Modified thinset mortar, 50 lb bag | 1 bag | $15 – $30 |
| Sanded grout, 25 lb bag | 1 bag | $10 – $20 |
| Backer board screws and seam tape | 1 box + 1 roll | $10 – $15 |
| Tile spacers, 1/8 in | 1 bag | About $5 |
| Wax ring (the toilet has to come up) | 1 | $3 – $8 |
| Grout sealer (optional but recommended) | 1 bottle | $10 – $15 |
Total cost
Materials come to about $150 – $385 for the whole floor — comfortably inside the $3.00 – $11.00 per sq ft materials range in our Tile Installation Cost per Square Foot (2026 Guide). Porcelain tile at $3.00 – $8.00 per sq ft instead of ceramic pushes the tile line to $150 – $400 and the total up with it.
Hiring it out instead: at $8.00 – $23.00 per sq ft installed, a professional job totals about $320 – $920 for 40 sq ft — and expect small-job minimums to keep real quotes toward the middle of that range even though the floor is small. If the old floor is tile that has to come up first, removal and disposal commonly add $2 – $4 per sq ft on top.
Calculate your own project
Different room size or tile format? Our Tile Calculator runs the same calculation with your measurements — area, tile size, grout joint, and waste — and returns tiles and boxes.
The job in seven steps
- Pull the toilet and clear the floor: shut off the water, drain and remove the toilet, and plug the flange with a rag. Remove baseboards if they will trap the new floor height.
- Check the subfloor: it must be flat, solid, and bounce-free. Tile over a flexing floor cracks — fix deflection before anything else.
- Lay backer board: bed the three sheets in thinset, screw them down on the printed pattern, and tape the seams with mesh tape and thinset.
- Dry-lay the layout: find the center, snap chalk lines, and check the cuts at the walls and doorway before mixing anything.
- Set the tile: spread thinset with a 1/4 in notched trowel in small sections, set each tile with a slight twist, and keep the 1/8 in spacers honest.
- Grout after curing — usually the next day — packing joints fully, then washing the haze off with a barely damp sponge.
- Seal and reset: seal the grout once it cures, set the toilet on a new wax ring, and caulk the tub and wall junctions with silicone, not grout.
FAQ
How many tiles do I need for a 40 sq ft bathroom floor?
With 12 × 12 in tiles and 10% waste, 44 tiles — sold as 5 boxes of 10. Larger formats need fewer, bigger cuts; small mosaics come on sheets and are counted by the square foot instead.
How much thinset does a 40 sq ft floor take?
One 50 lb bag. A bag covers roughly 40–60 sq ft under 12 × 12 in tiles with a 1/4 in notched trowel, and the same bag also beds the backer board — buy one, and a second only if your trowel or tile size is larger.
Can I tile over the existing bathroom floor?
Sometimes. Tile needs a flat, rigid, well-bonded surface: sound sheet vinyl on a solid subfloor can work with the right preparation, but loose, cushioned, or damaged floors have to come up, and every layer you keep raises the floor height at the doorway and toilet flange.
Do I really need backer board?
On a wood subfloor, yes — tile and grout are not waterproof or structural, and backer board gives them a stable, water-tolerant base. On a sound concrete slab you can tile directly after proper prep.
How long does retiling a small bathroom floor take?
A realistic weekend plus curing time: day one for backer board and setting tile, day two for grout after the thinset cures, and grout sealer a few days later. The toilet is out of service from step one until the reset, so plan around a second bathroom if you have one.
Related guides and calculators
Price the rates behind this estimate in the Tile Installation Cost per Square Foot (2026 Guide), put the same skills to work on the Kitchen Backsplash Cost (2026 Guide), and measure any room with the Square Footage Calculator.
Estimates only. Prices are typical US ranges checked in November 2026 and vary widely by region, product, and contractor. Confirm current prices and get written quotes before committing to a project.