Backer Board Calculator
Your substrate
Floors use a tighter screw pattern than walls.
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.
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Tools the pros use for this job
Cement Backer Board
Hard-to-Find Fastener Phillips Self-Piercing Cement Board Screws, Durable Steel Hardware Fasteners for Home Improvement, DIY, Construction, 8 x 1-1/4, Pack of 168
$11.11
Check price on AmazonThe standard 3×5 sheets every tile floor and shower starts with.
Mixing Paddle
IMAYCC Cement Mixer, 2100W Electric Concrete Mixer with 6 Speed, 110V Handheld Mud Mixer for Motar,Paint, Grout, Plaster, Thinset,Fodder Stirring Tool
$48.99
Check price on AmazonBoards are bedded in thinset — you will be mixing a lot of it.
Waterproofing Kit
Backer board is not waterproof — this membrane layer is.
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Prices as of Oct 10, 2026, 6:33 AM UTC. Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.
Waterproofing the board? See our shower waterproofing buying guide.
Choosing mortar? See our thinset buying guide.
Slab not flat enough for large tile? Use the self leveler calculator.
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How this calculator works
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.
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.
Frequently asked questions
How many cement boards do I need?
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.
How many cement boards do I need for a shower?
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.
What thickness of cement board for floors and 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.
How many screws per sheet of backer board?
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.
Do I need thinset under backer board on a floor?
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.
Is cement board waterproof?
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.
Can I tile directly over plywood?
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.
Related calculators
- Thinset & Mortar CalculatorBags of thinset by trowel notch size and coverage.
- Shower Tile CalculatorWalls, floor, curb, and niche for a full shower surround.
- RedGard CalculatorGallons and pails of RedGard for shower walls and pan at the data-sheet coverage rates.
- DITRA CalculatorDITRA rolls, thin-set bags under and over the membrane, and the trowel for each.
- Self Leveler Calculator50 lb bags of self-leveling compound by area and depth.
- Tile Weight CalculatorTotal tile weight for delivery, upstairs floors, and structure.
Guides worth reading next
- How to Measure a Room for Tile (Step by Step)Measure any room for floor or wall tile: handle closets and alcoves, convert inches to decimals, subtract fixtures, and add the right waste percentage.
- Choosing the Right Tile Size for Your RoomHow tile size changes a room: when 12×24 beats 4×4, why small rooms can take large tile, grout line math, and the flatness rule for big formats.
- Sanded vs Unsanded vs Epoxy Grout: Which One Do You Need?Grout types explained by joint width and location: when sand scratches tile, why epoxy wins in showers, and how much of each type a bag actually covers.