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One 3x5 cement board covers 15 sq ft. Enter your floor or shower area for the sheet count, screws (32 per floor sheet) and mesh tape, with 8% waste.
With these inputs:
| Result | Value |
|---|---|
| Sheets to buy | 5 |
| Coverage per sheet | 15 sq ft |
| Includes 8% cutting waste | Yes |
| Backer screws | ~160 |
| Mesh tape rolls (150 ft) | 1 |
Score-and-snap cuts like drywall — no wet saw needed. Wear a mask; cement dust is nasty.
<> Sheets come mainly in 3×5 ft (15 sq ft) for floors and 4×8 ft (32 sq ft) for walls. We add 8% for cutting waste and round up. On floors, use 1/4 in board bedded in thinset; on walls, 1/2 in board screwed directly to studs. Not sure board is the right base? Compare it with membranes and plywood in our tile underlayment guide . Screws: roughly 32 per sheet on floors (8-inch grid) and 24 on walls — always alkali-resistant backer board screws, never drywall screws, which corrode. Seams get alkali-resistant mesh tape embedded in thinset.
Divide the area by the sheet size and add about 8% for cuts. A 3x5 sheet covers 15 sq ft, so a 60 sq ft bathroom floor is 64.8 sq ft with waste — round up to 5 sheets. On walls, count each wall separately, because offcuts rarely fit the next wall.
Add up the wall area to be tiled (each wall's width times the tile height) and divide by the sheet size, rounding up per wall. A standard 5 ft tub alcove tiled to about 6 ft covers roughly 60–65 sq ft, which is 5 sheets of 3x5 board before offcuts; 4x8 sheets cut the seam count on walls.
1/4 in cement board on floors, where it adds no strength and only gives the tile a stable surface over a 5/8 in or thicker plywood subfloor. 1/2 in on walls and in showers, where it has to span the studs on its own at 16 in centers.
Plan on about 32 screws per 3x5 sheet on floors (an 8 in grid) and about 24 on walls, set 3/8–1/2 in from the edges. Use backer-board screws, not drywall screws, which corrode in mortar.
Yes — always. The thinset bed fills voids so the board cannot rock; the screws just clamp it while the thinset cures. Screws alone leave hollow spots that crack tile.
No. Cement board is water-stable (it will not swell or rot) but water passes through it. Showers still need a waterproofing membrane over or behind it.
Not recommended — plywood expands and contracts with humidity and flexes under load, cracking grout and tile. A backer board or uncoupling membrane isolates the tile from that movement.
Need the whole roof at once? The free roofing calculator works out roof area, squares, shingle bundles, underlayment, drip edge, ridge cap and installed cost from one set of measurements.