How it works
The formulas
tile cost = price per sq ft × (boxes × sq ft per box)
grout lb = sq ft × 144 × (L + W) ÷ (L × W) × joint × thickness × 0.0672
grout bags = lb ÷ 25, rounded up
thinset bags = floor sq ft ÷ sq ft per bag, rounded up
Assumptions
- Waste is 10% for a straight layout and 15% for diagonal or herringbone, where more tiles are cut. Add a few more percent for a tricky room or tile that chips easily. These are rules of thumb.
- Tile is sold by the box and priced per sq ft. We round the boxes up first, then price the full 15 sq ft in each box, because you pay for the whole box. That is why the cost is a little higher than floor area times price.
- Grout uses the joint volume method used by grout makers' calculators: the length of joint in a sq ft of floor, times the joint width, times the tile thickness, times the weight of the grout. Sanded grout weighs about 0.0672 lb per cubic inch (1.86 g/cm³). We derived this conversion ourselves, so treat it as an estimate and compare it with the coverage chart on the bag. Most of the grout goes in the joints; expect some to be lost in mixing and cleanup.
- Joints under 1/8 in (that is, 1/16 in) take unsanded grout. The count is the same, but buy unsanded bags and use your own price.
- Thinset (a 50 lb bag) covers about 60 sq ft with a 1/4 × 3/8 in square-notch trowel, the low end of the 60 to 67 sq ft on Custom Building Products' charts. Tile with a side of 15 in or more gets a 1/2 × 1/2 in trowel at about 40 sq ft per bag (a rule of thumb; check the bag, since large tile may also need back-buttering).
- Metric: type meters. The floor is converted to feet for the math. Tile and joint sizes stay in inches, and tile, grout and thinset are still bought in US sq ft, boxes and pounds.
Worked example
A 10 × 8 ft bathroom floor, 12 × 12 in tile, 1/8 in joints, 3/8 in thick, straight layout
- Floor: 10 × 8 = 80 sq ft
- Add 10%: 80 × 1.10 = 88.0 sq ft
- Boxes: 88.0 ÷ 15 = 5.87, so buy 6 boxes (90 sq ft)
- Tile cost: 90 sq ft × $9.13 (the middle of our typical range) = $821.25
- Grout: 80 × 144 × (12 + 12) ÷ (12 × 12) × 1/8 × 3/8 × 0.0672 = 6.0 lb, so 1 bag of 25 lb
- Thinset: 80 ÷ 60 = 1.33, so 2 bags
Common floor sizes, 12 × 12 in tile
| Floor | Sq ft | Boxes of tile | Grout bags | Thinset bags |
|---|---|---|---|---|
| 5 × 8 bath | 40 | 3 | 1 | 1 |
| 10 × 10 room | 100 | 8 | 1 | 2 |
| 12 × 12 kitchen | 144 | 11 | 1 | 3 |
| 15 × 20 room | 300 | 22 | 1 | 5 |
12 × 12 in tile at 15 sq ft per box, 1/8 in joints, 3/8 in thick, straight layout with 10% extra, 60 sq ft of thinset per bag.
Questions people ask
How much tile do I need for a 10x10 floor?
A 10 × 10 ft floor is 100 sq ft. With 10% extra that is 110 sq ft, or 8 boxes of 12 × 12 tile at 15 sq ft per box. A diagonal layout needs 8. Always divide by the sq ft on your own box label.
How much extra tile should I buy?
10% for a straight layout and 15% for diagonal or herringbone. Small rooms with many cuts, and large tile, can need more. Keep a spare box: dye lots change, and a future repair will not match a new batch.
How much grout do I need per sq ft?
It depends on tile size, joint width and thickness. For 12 × 12 in tile with 1/8 in joints and 3/8 in thickness it is about 0.08 lb per sq ft. For 3 × 6 subway tile with 1/16 in joints and 1/4 in thickness it is 0.08 lb, and for 12 × 12 in tile with 1/4 in joints it is 0.15 lb. Small tile and wide joints use the most.
Sanded or unsanded grout?
Use sanded grout for joints 1/8 in and wider. The sand keeps wide joints from shrinking and cracking. Use unsanded grout for joints under 1/8 in, and for polished marble or other tile that sanded grout can scratch. The calculator prices sanded grout; type the price of unsanded if that is what you need.
How much thinset do I need?
A 50 lb bag covers about 60 sq ft with a 1/4 × 3/8 in trowel, and about 40 sq ft with a 1/2 × 1/2 in trowel for large tile. A 100 sq ft floor of 12 × 12 tile needs 2 bags; with 12 × 24 tile it needs 3. Uneven floors and back-buttering use more.