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.
Do this math on the job site — in the free app
Smart Tile Calculator for Android: offline, in your pocket, no ads. iPhone version coming soon.
Tools the pros use for this job
Cement Backer Board
BXI Inorganic Ceramic Fiber Thermal Insulation Board(2732F) - 12'' X 8'' X 0.4'', Pack of 1 - High Density - Flame Retardant, Heat Resistant, High Temperature Insulation
Check price on AmazonThe standard 3×5 sheets every tile floor and shower starts with.
Mixing Paddle
Edward Tools Paint and Mud Mixer for Drill - Mixes 1 to 3 Gallons - 15 3/4" Length - 5/16" Hex Shaft - Zinc Plated Steel - Reinforced Weld - Non Slip Hex Head - Easy Clean - Paint Mixer Attachment
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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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
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.
- Self-Leveling Compound CalculatorBags of leveler by area and depth of the low spots.
- 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.