# Flooring and tile calculator

> Tile calculator: tiles and boxes for a floor or wall from room size, tile size, grout joint and waste allowance, plus grout in litres and kg.

Interactive version: https://www.calcopenly.com/construction/tile-calculator
Subject: Construction and home calculators

The tile count is the area divided by the area one tile covers with its grout joint, (tile length + joint) × (tile width + joint). A waste allowance for cuts and breakage is added, then the count is rounded up to whole tiles and whole boxes. Grout volume per m² is (A + B) ÷ (A × B) × tile thickness × joint width, with A and B the tile sides and all four in millimetres.

The default 4 × 3 m floor in 600 × 300 mm tiles with 3 mm joints takes 65.7 tiles laid edge to edge. With 10% waste that is 73 tiles, or 10 boxes of 8, plus 1.62 L of grout (2.6 kg).

The waste presets are this calculator's rules of thumb: 10% for a straight lay, 15% for diagonal and 20% for herringbone, which cut more tiles at the edges. The drawing shows a straight lay.

## Inputs

- **Area length**
- **Area width**
- **Tile length**
- **Tile width**
- **Grout joint**
- **Tile thickness (joint depth)**
- **Waste allowance**: Covers cuts and breakage. Diagonal and herringbone layouts cut more tiles at the edges.
- **Tiles per box**
- **Price per box**

## Results

- Tiles to buy (tiles) — main result
- Boxes to buy (boxes)
- Area (m²)
- Area (ft²)
- Grout volume (L)
- Grout (dry weight) (kg)
- Tile cost

## Formula

$$
N = \left\lceil \frac{A}{(\ell_t + j)(w_t + j)} \times (1 + \text{waste}) \right\rceil,\qquad G = \frac{\ell_t + w_t}{\ell_t w_t} \cdot t \cdot j \cdot A
$$

## Worked examples

### 4 × 3 m floor, 600 × 300 mm tiles, 3 mm joints, 10% waste

- Area length: 4 m
- Area width: 3 m
- Tile length: 600 mm
- Tile width: 300 mm
- Grout joint: 3 mm
- Waste allowance: 10%
- Tiles per box: 8
- **Area: 12 m²**
- **Tiles to buy: 73 tiles**
- **Boxes to buy: 10 boxes**
- **Grout volume: 1.62 L**
- **Grout (dry weight): 2.59 kg**
- **Tile cost: 400.00**
- Checked against: Python decimal: 12 ÷ (0.603 × 0.303) = 65.68 × 1.1 = 72.25 → 73; grout (900/180000) × 9 × 3 × 12 = 1.62 L × 1.6 kg/L (Mapei formula); 10 boxes × 40 = 400

### 12 × 10 ft, 12 in tiles, ⅛ in joints, diagonal 15%

- Area length: 12 ft
- Area width: 10 ft
- Tile length: 12 in
- Tile width: 12 in
- Grout joint: 0.125 in
- Tile thickness (joint depth): 0.375 in
- Waste allowance: 15%
- Tiles per box: 10
- **Area: 120 ft²**
- **Tiles to buy: 136 tiles**
- **Boxes to buy: 14 boxes**
- **Grout volume: 2.21 L**
- Checked against: Python decimal: 120 ft² ÷ (12.125 in)² = 117.54 × 1.15 = 135.17 → 136 tiles → 14 boxes of 10; Mapei grout formula in mm

### Edge: tiles fit exactly, no joint, no waste

- Area length: 3 m
- Area width: 3 m
- Tile length: 300 mm
- Tile width: 300 mm
- Grout joint: 0 mm
- Waste allowance: 0%
- Tiles per box: 10
- **Tiles to buy: 100 tiles**
- **Boxes to buy: 10 boxes**
- **Grout volume: 0 L**
- Checked against: Hand calculation: 3 m ÷ 0.3 m = 10 tiles each way = 100 tiles, 10 boxes; a zero-width joint needs no grout

## Questions

### How many tiles do I need per square metre?

Divide 1 m² by the area of one tile plus its joint. A 600 × 300 mm tile with a 3 mm joint covers 0.603 × 0.303 = 0.1827 m², so 1 m² takes 5.47 tiles; 300 × 300 mm tiles take 10.89. Multiply by the whole area before rounding up: rounding 5.47 up to 6 per m² would overbuy by about 10%.

### How many tiles do I need for 100 square feet?

About 98 twelve-inch tiles before waste. A 12 × 12 in tile with a ⅛ in joint covers 12.125 × 12.125 in, or 1.021 ft², so 100 ft² takes 97.95 tiles. Adding 10% for cuts and breakage gives 107.7, rounded up to 108 tiles.

### How much extra tile should I buy for waste?

This calculator's presets add 10% for a straight lay, 15% for a diagonal lay and 20% for herringbone, because angled layouts cut more tiles along every wall. On the default 12 m² floor those give 73, 76 and 79 tiles of 600 × 300 mm.

### How much grout do I need?

Multiply (A + B) ÷ (A × B) by tile thickness and joint width, all in mm, to get litres of joint per m². For 600 × 300 mm tiles 9 mm thick with 3 mm joints that is 900 ÷ 180,000 × 9 × 3 = 0.135 L per m², or 1.62 L for 12 m². The calculator converts at 1.6 kg per litre; check the grout bag's own coverage table.

### Do grout joints change the number of tiles needed?

Yes, they lower it slightly, because each tile plus its joint covers more floor. A 600 × 300 mm tile covers 0.18 m² on its own and 0.1827 m² with a 3 mm joint, so 12 m² needs 65.7 tiles instead of 66.7 before waste. For 50 × 50 mm mosaic with 3 mm joints, each tile's footprint grows by 12.4%.

### How accurate is the flooring and tile calculator?

Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 3 worked examples whose answers come from independent sources; for example, “4 × 3 m floor, 600 × 300 mm tiles, 3 mm joints, 10% waste” is checked against Python decimal: 12 ÷ (0.603 × 0.303) = 65.68 × 1.1 = 72.25 → 73; grout (900/180000) × 9 × 3 × 12 = 1.62 L × 1.6 kg/L (Mapei formula); 10 boxes × 40 = 400.

### Where does the method come from?

Mapei grout calculator — consumption (A + B)/(A × B) × C × D × 1.6 = kg/m²; TCNA Handbook for Ceramic, Glass, and Stone Tile Installation — joint widths and layouts.

## Sources

- [Mapei grout calculator — consumption (A + B)/(A × B) × C × D × 1.6 = kg/m²](https://www.mapei.com/gb/en/tools-and-downloads/product-calculator/grouts)
- TCNA Handbook for Ceramic, Glass, and Stone Tile Installation — joint widths and layouts