How Much Backer Board Do I Need for a Shower?
Quick answer: add the three tiled walls (back + two sides), subtract the door opening, add 10–15% waste, and divide by 15 sq ft per 3×5 sheet or 32 sq ft per 4×8 sheet. A 36×72 shower tiled to 6 ft needs about 72 sq ft — 5 sheets of 3×5 or 3 sheets of 4×8.
- The backer board formula
- 3×5 vs 4×8 sheets
- Backer types
- Worked example: 36×72 shower
- Common mistakes
- FAQ
The backer board formula
Backer board covers the same walls as your tile: back wall (width × height) plus two side walls (depth × height), minus the door opening, plus 10–15% waste. Divide by the sheet coverage — 15 sq ft for 3×5 ft board, 32 sq ft for 4×8 ft board — and round up to whole sheets. Board comes in 1/2-inch and 5/8-inch thicknesses; 1/2-inch is standard for walls.
3×5 vs 4×8 sheets
3×5 ft sheets are the DIY favorite: one person can handle them and they cut cleanly with a scoring knife. 4×8 sheets mean fewer seams and faster coverage but are heavy and awkward inside a small enclosure. For a standard shower, 3×5 sheets in 5/8 or 1/2 inch are the practical choice.
Backer types
Cement board (e.g., Durock, HardieBacker) is the classic wet-area backer. Fiber-cement and foam tile backers (lighter, waterproof, more expensive) are modern alternatives. Regular drywall — even green drywall — is not rated for direct spray zones. Whatever you use, tape the seams with alkali-resistant mesh and set them in thinset before tiling.
Worked example: a 36×72 shower tiled to 72 inches
- Back wall: 72 × 72 = 36 sq ft
- Two side walls: 36 × 72 each = 36 sq ft
- Minus door 11 sq ft = 61 sq ft
- Add 15% = 70 sq ft → 5 sheets of 3×5 (75 sq ft) or 3 sheets of 4×8 (96 sq ft)
Common mistakes
- Forgetting the door cutout. The opening is real board you don't need — subtract it before buying.
- Using 4×8 sheets alone in a small shower. Full sheets rarely fit an enclosure; you'll cut them anyway, so the larger size saves less than it seems.
- Regular drywall behind tile. It swells and fails in wet areas. Use cement or waterproof backer.
- Skipping seam tape. Untaped backer-board seams crack the tile above. Tape every seam in mesh and thinset.
FAQ
Measure the three tiled walls (width × height each), add them together, add 10–15% waste, and divide by 15 sq ft (3×5 sheet) or 32 sq ft (4×8 sheet). A 36×72 shower tiled to 6 ft needs about 72 sq ft — 5 sheets of 3×5 or 3 sheets of 4×8.
Add the area of the three walls you'll tile, subtract the door opening, add 10–15% for cuts, and divide by the sheet coverage: 15 sq ft for a 3×5 sheet, 32 sq ft for a 4×8 sheet.
Use 3×5 ft cement board (15 sq ft per sheet) for most showers — it's manageable by one person and cuts cleanly. 4×8 sheets mean fewer seams but are heavy in a small enclosure.
No — regular drywall breaks down in wet areas. Use cement backer board or a waterproof tile backer. Green drywall is acceptable only outside the direct spray zone.
Add 10–15% for cuts around the valve, corners, the niche and the curb. Because sheets are large, odd wall heights often waste a chunk — round up to whole sheets.