Grout Calculator
Find how much tile grout to buy from the area, tile size, tile thickness and joint width. Advanced adds floor and wall areas, mosaic sheets, grout density, waste, cost and a tile count.
Tile thickness is the depth of the joint. Most floor tiles are 8–10 mm (about 3/8 in), wall tiles 6–8 mm, mosaics 4–6 mm. Fractions work: type 1/8.
Typical assumptions: about 1,900 kg/m³ for set cement grout and 1,600 for epoxy. Type your product’s figure if you know it.
Grout left in the bucket, on the float and in the sponge. 10% is typical; use 15–20% for rough or textured tiles.
How your grout is worked out
Joint volume for each square metre or foot, times the area, times the grout's weight, plus extra.
- 1
Area to grout
10 ft × 10 ft= 100 sq ft
- 2
Joint per area
(12+12) ÷ (12×12)× 3/8 × 1/8 in= 1.13 in³/sq ft
- 3
Volume × weight
112.5 in³ = 1.84 L× 1,900 kg/m³= 3.5 kg
- 4
Add extra, bag it
3.5 kg × 1.10= 3.85 kg= 1 bag of 10 lb
Read more: the formula, worked examples, typical amounts and grout types
Grout fills the joints between tiles. The amount depends on how much joint there is in each square metre or foot (small tiles have far more joints than big ones), how wide the joint is and how deep it is (the tile thickness). Multiply that volume by the grout’s weight, add a little extra, and divide by the bag size.
The formula
joint volume per area = (tile length + tile width) ÷ (tile length × tile width) × tile thickness × joint width
joint volume = area × joint volume per area
grout weight = joint volume × grout density
grout to buy = grout weight × (1 + waste % ÷ 100)
bags = grout to buy ÷ bag size, rounded up
tiles = area ÷ ((tile length + joint) × (tile width + joint)), rounded up
Use one unit for all the sizes: in millimetres with the area in m², the answer is litres per m². Density is typically 1,900 kg/m³ (1.9 kg per litre) for cement grout and 1,600 kg/m³ for epoxy; these are our typical assumptions, not product data.
Worked example
A floor 10 ft × 10 ft is 100 sq ft, or 100 × 144 = 14,400 sq in. The tiles are 12 × 12 in, 3/8 in (0.375 in) thick, with 1/8 in (0.125 in) joints.
Joint volume per square inch: (12 + 12) ÷ (12 × 12) × 0.375 × 0.125 = 24 ÷ 144 × 0.046875 = 0.0078125 in, which is 0.0078125 × 144 = 1.125 cubic inches per sq ft. For 100 sq ft that is 112.5 cubic inches. One cubic inch is 0.016387064 litres, so that is 1.8435 litres, or 0.0018435 m³.
Cement grout at 1,900 kg/m³: 0.0018435 × 1,900 = 3.50 kg. With 10% extra: 3.50 × 1.10 = 3.85 kg, which is 3.85 ÷ 0.45359237 = 8.49 lb. One 10 lb bag is enough, with about 1.5 lb to spare.
Tiles: each tile with its share of the joint covers 12.125 × 12.125 = 147.015625 sq in. 14,400 ÷ 147.015625 = 97.95, so 98 tiles, or 97.95 × 1.10 = 107.74, so 108 tiles with 10% extra.
In metric: a floor 2.5 m × 4 m is 10 m². With 30 × 30 cm tiles 8 mm thick and 3 mm joints: (300 + 300) ÷ (300 × 300) × 8 × 3 = 0.16 litres per m², × 10 m² = 1.6 litres. × 1.9 kg per litre = 3.04 kg, + 10% = 3.344 kg, so one 5 kg bag.
Typical grout for common tiles
| Tile | Thick × joint | kg per m² | lb per 100 sq ft |
|---|---|---|---|
| 60 × 60 cm | 10 × 3 mm | 0.19 | 3.89 |
| 30 × 30 cm | 8 × 3 mm | 0.30 | 6.23 |
| 20 × 20 cm | 7 × 2 mm | 0.27 | 5.45 |
| 10 × 10 cm | 6 × 2 mm | 0.46 | 9.34 |
| 12 × 24 in | 3/8 × 1/8 in | 0.28 | 5.79 |
| 12 × 12 in | 3/8 × 1/8 in | 0.38 | 7.72 |
| 3 × 6 in subway | 5/16 × 1/16 in | 0.47 | 9.65 |
| 2.5 × 2.5 cm mosaic | 4 × 2 mm | 1.22 | 24.91 |
| 1 × 1 in mosaic | 1/4 × 1/16 in | 1.51 | 30.89 |
Cement grout at 1,900 kg/m³, no extra for waste. Epoxy at 1,600 kg/m³ is about 16% lighter for the same joints.
Notes
- Check your grout maker’s coverage chart. These results are estimates. Real use depends on the product, how full you pack the joints and how much is wiped away.
- If the tiles sit on a thick bed of adhesive that shows in the joint, the joint is a little shallower than the tile is thick, so you may need slightly less.
- Joints that are wider than 1/8 in (3 mm) usually take sanded grout; narrower joints take unsanded grout. Epoxy suits showers and kitchens.
- Buy all the grout from the same batch so the colour matches, and keep a little for repairs.
Densities are typical figures for set grout, not taken from any one product. Checked on 13 October 2026.
Common questions
How much grout do I need?
Work out the joint volume: (tile length + tile width) ÷ (tile length × tile width) × tile thickness × joint width gives the volume for each unit of area. Multiply by the area and by the grout’s weight. For 100 sq ft of 12 × 12 in tiles, 3/8 in thick, with 1/8 in joints, that is 112.5 cubic inches, about 3.5 kg (7.7 lb), or 3.85 kg (8.5 lb) with 10% extra.
How many bags of grout do I need?
Divide the grout you need, with extra for waste, by the bag size and round up. 3.85 kg is one 10 lb (4.54 kg) bag. Small tiles, wide joints and thick tiles use much more grout, so mosaics can need three or four times as much as big floor tiles.
What does grout weigh?
Set cement grout typically weighs about 1,800–2,000 kg per m³ (this calculator assumes 1,900) and epoxy grout about 1,500–1,700 (we assume 1,600). These are typical figures, not product data. Your grout maker’s coverage chart is the best guide.
How wide should grout joints be?
Typically 1/16–1/8 in (2–3 mm) for rectified tiles and walls, 1/8–3/16 in (3–5 mm) for most floor tiles, and 1/4 in (6 mm) or more for rustic or handmade tiles. Many makers ask for joints of at least 1/16 in (1.5–2 mm). Follow the tile maker’s advice.
Sanded or unsanded grout?
In the US, unsanded grout is usually used for joints up to 1/8 in and sanded grout for wider joints. Both weigh about the same once set. Epoxy grout suits wet, stain-prone areas like kitchen splashbacks and showers.
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