How this calculator works
It multiplies the room’s length by its width, adds a cut allowance for the layout you choose and divides by the size of one tile to get whole tiles. Then it rounds up to full boxes using the coverage printed on the box.
Thinset is based on the trowel notch a tile that size usually needs (published bag-chart coverage, conservative end). Grout comes from the volume of the joints: tile size, joint width and tile thickness. Both get 10% extra for mixing.
floor area = length × width
tiles = floor area × (1 + cut allowance) ÷ area of one tile
boxes = tiles × area of one tile ÷ box coverage
thinset lb = floor area ÷ trowel coverage per 50 lb bag × 50 × 1.1
grout lb = area × 144 × (L + W) ÷ (L × W) × joint × depth × 0.065 × 1.1Worked example
A 12′ × 10′ kitchen is 120 sq ft. With 12″ × 24″ tile (2 sq ft each) laid straight, add 10% for cuts: 132 sq ft, or 66 tiles. At 16 sq ft per box that is 8.25 boxes, so you buy 9. Tile this size goes down with a ½″ square-notch trowel at about 40 sq ft per 50 lb bag: 120 ÷ 40 × 50 × 1.1 = 165 lb of thinset, three 50 lb bags plus one 25 lb bag. ⅛″ joints on ⅜″ tile need about 7.2 lb of grout, one 10 lb bag of sanded grout.
Tips before you buy
- Buy every box from the same lot (shade and caliber are printed on the box) so color and size match across the floor.
- Keep one or two spare tiles after the job. A cracked tile years later is easy to replace only if you still have a matching one.
- Lay the tiles out dry across the middle of the room first so you do not end up with thin slivers against a wall.
- Large tiles (over 15″ on a side) need a flat floor; check with a straightedge and plan for leveling clips or self-leveler if needed.
Questions
- How much extra tile should I buy?
- Add about 10% for a straight or offset layout, 15% for diagonal and up to 20% for herringbone, because angled cuts waste more tile. Small or oddly shaped rooms with many corners can need a little more.
- Why do I need the box coverage?
- Tile is sold by the box, and the number of tiles per box changes with size and brand. The label states the square feet (or m²) each box covers; enter that figure and the calculator rounds to whole boxes.
- Which trowel notch does floor tile need?
- A common rule is a ¼″ × ¼″ square notch for tile up to 8″, ¼″ × ⅜″ for tile up to about 15″, and ½″ × ½″ for larger tile. Always check that the back of the tile is fully bedded by lifting one after setting it.
- Should I return leftover boxes?
- Most stores take back unopened boxes, so rounding up costs little. Keep at least a few loose tiles from the same lot for future repairs before you return anything.