Cement Board Calculator
How many cement backer board sheets for a shower, wall or floor: 3×5, 4×8 or 0.90×1.20 sheets with waste, backer-board screws, alkali-resistant mesh tape and thinset bags.
How it works
sheets = ⌈area × (1 + waste) ÷ sheet area⌉ · screws per sheet = (columns) × (rows) at 20 cm (8″), columns on studs for walls · tape ≈ area × (1/width + 1/height)
Cement backer board (Durock, HardieBacker, Superboard, Aquapanel and similar) is the tile substrate for showers, wet walls and floors. Manufacturers such as USG specify corrosion-resistant backer-board screws every 8″ (20 cm) along each stud on walls, and every 8″ in both directions over the whole sheet on floors, where the board is also set in a bed of thinset over the plywood. Every joint gets 2″ (5 cm) alkali-resistant fiberglass mesh tape embedded in thinset. The calculator rounds sheets up after a waste allowance, typically 10% for walls with cut-outs.
Worked example
12 m² of wall with 4 × 8 ft (1.22 × 2.44 m, 2.97 m²) sheets: 12 × 1.10 ÷ 2.97 = 4.4 → 5 sheets. On studs 40 cm apart with screws every 20 cm each sheet takes 4 × 13 = 52 screws, 260 in all; the joints need about 15 m of alkali-resistant mesh tape (1 roll), and the sheets cost $75.00 at $15 each.
Sources: USG Durock cement board — installation guide · Tile Council of North America — TCNA Handbook
Frequently asked questions
How many screws per sheet of cement board?
About 50 on a 4×8 ft wall sheet (4 studs × 13 screws at 8″ spacing) and about 90 on a floor, where screws go every 8″ in a grid. A 3×5 sheet takes roughly 25–30 on a wall.
Do I need thinset under cement board on a floor?
Yes. Manufacturers require a bed of modified thinset troweled with a ¼″ (6 mm) notch between the subfloor and the board to fill voids, then screws every 8″. Walls do not need it.
What tape do I use on cement board joints?
Alkali-resistant fiberglass mesh tape, 2″ (5 cm) wide, embedded in thinset — not paper or regular drywall tape, which breaks down in cement.
What size cement board should I buy?
3×5 ft (0.91 × 1.52 m) sheets are light and fit tub surrounds; 4×8 ft (1.22 × 2.44 m) sheets mean fewer joints on large walls and floors. Thickness is usually ½″ (12.7 mm) for walls and ¼″ (6 mm) for floors over plywood.
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This calculator is for educational purposes. Double-check important results before acting on them.