How the tile calculator works
Each tile covers its own area plus its share of the grout joint around it. The calculator divides your total area (with waste) by that, and rounds up. Grout is worked out from the total length of joints, multiplied by their width and depth (the tile’s thickness).
The formula
tiles = area × (1 + waste %) ÷ ((tile length + joint) × (tile width + joint))
grout = area × (tile length + tile width) ÷ (tile length × tile width) × joint width × tile thickness × density
The grout estimate uses about 1.8 kg of cement-based grout per litre of joint, plus 10% extra.
Tips
- Large tiles need more waste than you’d think, because each cut throws away a bigger piece. 12×24 in tiles in a small bathroom can waste 15% or more.
- Buy all your tile at once and check that the boxes share a lot or shade number. Colour varies between batches.
- Grout joint width: 1/8 in (3 mm) is common for rectified porcelain; hand-made or rustic tile needs a wider joint. The tile box often lists a minimum.
- Bathrooms: tile over a proper backer and waterproofing membrane on shower walls, not regular drywall.