Quick takeaway: Divide room area by square tile area, add your waste allowance and round up to whole tiles. A 20 × 20 ft room using 24 × 24 in tiles needs 110 tiles with 10% allowance, or 11 boxes of 10 tiles.
Calculate carpet tiles and boxes
Measure the room in feet and the side of each square tile in inches. Choose an allowance for edge cuts, pattern matching and spare replacements. Enter the manufacturer's tiles-per-box count to convert the estimate into whole boxes.
The calculator estimates a rectangular room using square tiles. Irregular rooms, stairs and rectangular carpet planks need a separate layout or takeoff.
Carpet tile formula
Tiles = ceil((Room length × Room width × 144 × (100 + Waste %)) ÷ (Tile side² × 100))
There are 144 square inches in one square foot. A 24-inch square tile covers 24 × 24 ÷ 144 = 4 sq ft. Whole boxes are calculated by dividing the rounded tile count by tiles per box and rounding up again.
Worked example for a 20 by 20 ft room
For a 20 ft × 20 ft room, 24-inch square tiles, a 10% allowance and 10 tiles per box:
- Room area = 20 × 20 = 400 sq ft.
- Tile area = 24 × 24 ÷ 144 = 4 sq ft.
- Tile count before allowance = 400 ÷ 4 = 100 tiles.
- Add allowance = 100 × 110 ÷ 100 = 110 tiles.
- Order quantity = round 110 ÷ 10 up = 11 boxes.
If your supplier sells boxes of 12, the same 110-tile estimate requires 10 boxes, containing 120 tiles. Box rounding can add spare tiles beyond the allowance you entered.
Choose a waste allowance
The default 10% is a planning allowance, not a universal manufacturer requirement. Adjust it for the tile, installation pattern, room shape and spare stock you want to keep. A room with many corners or obstructions may need a detailed layout rather than a larger blanket percentage.
Evidence note: Interface's carpet tile installation guidance distinguishes backing types and installation methods, and reports low waste for specific non-directional products. This supports using product-specific instructions rather than treating 10% as an exact rule. This calculator estimates material quantity; it does not check subfloor moisture, adhesive suitability or installation requirements.
Common Mistakes
- Mixing feet and inches. Room dimensions are in feet; tile dimensions are in inches.
- Entering 50 for a 50 cm tile in an inch field. Convert 50 cm to about 19.685 inches first.
- Forgetting that the tile input assumes a square. A 12 × 24 in plank cannot be entered as a 24-inch square.
- Rounding tile count or boxes down, which can leave you short of materials.
- Assuming tiles generate no waste or that every installation pattern needs the same allowance.
- Using the area of a bounding rectangle for an L-shaped room. Split it into rectangles and account for the actual installation layout.
Square tile coverage reference
| Square tile size | Coverage per tile |
|---|---|
| 12 × 12 in | 1 sq ft |
| 18 × 18 in | 2.25 sq ft |
| 24 × 24 in | 4 sq ft |
Confirm the actual tile dimensions and pack quantity on your product label. This estimate does not include adhesive, connectors, trim, labor or subfloor preparation.