How to Calculate Tile and Grout for a Bathroom

Floor and wall tiles are usually different products, so keep them as separate lists from the start. For the floor, measure wall to wall. Tile under the vanity only if it’s freestanding or might be replaced later. Most people skip tiling under a fixed cabinet.

For a shower, measure each wall to the height you’re tiling, often to the ceiling or just above the shower head. Take off any window or niche you won’t tile across.

• Floor area: 7 × 5 = 35 sq ft
• One 12 × 24 in tile covers 2 sq ft, so 17.5 tiles before waste
• Small room, lots of cuts: allow 15%. 35 × 1.15 = 40.25 sq ft, which is 20.1 tiles, so 21
• At 8 tiles per box, that’s 3 boxes (24 tiles)

Why 15% here and not the usual 10%? In a small room a larger share of tiles get cut, and an off-cut from one side rarely fits the other. Large tiles make this worse, not better.

A 5 ft wide shower recess with two 3 ft side walls, tiled 7 ft high:

• Back wall: 5 × 7 = 35 sq ft
• Side walls: 2 × (3 × 7) = 42 sq ft
• Total: 77 sq ft

A 3 × 6 in subway tile covers 18 sq in, which is 0.125 sq ft. So 77 sq ft needs 616 tiles before waste, and about 709 with 15% for cuts around the valve, the corners and the edge trim. Boxes of small tile are sold by area or by count, so check the label before dividing.

A tiled niche adds its back and four sides to the total. Measure them like tiny walls.

If your grout’s data sheet has a coverage table for your tile size and joint width, use that. If not, the joint-volume formula works it out from the tile:

kg per m² = (A + B) ÷ (A × B) × C × D × density

A and B are the tile length and width, C is the joint depth (usually the tile thickness), D is the joint width, all in millimetres. Density is in kg per litre, from the data sheet. We’ll assume 1.6.

Shower walls (3 × 6 in subway, 5/16 in thick, 1/16 in joints): about 0.40 kg per m². 77 sq ft is 7.15 m², so 2.8 kg, or 3.1 kg (about 6.9 lb) with 10% for mixing and cleanup.

Floor (12 × 24 in, 3/8 in thick, 1/8 in joints): about 0.24 kg per m². 35 sq ft is 3.25 m², so 0.85 kg (about 1.9 lb) with 10% extra.

Small tiles need far more grout per square foot than large ones, because there’s more joint in every square. Mosaics on a shower floor can use several times as much as the wall tiles above them.

• Check that every box has the same batch or lot number. Shade varies between production runs, and the difference shows most in a small, well-lit room.
• Open a few boxes and blend tiles as you go, rather than finishing one box before starting the next.
• Keep a handful of spare tiles. A cracked tile five years from now is easy to replace if you kept some.
• Wet areas may need a specific grout type, membrane or sealant. Follow the tile and grout makers’ instructions for showers.

The tile calculator works out tiles and boxes with your waste allowance, and the grout calculator uses the joint formula or your product’s coverage figure. To total awkward floor shapes first, use the square footage calculator.