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Generated on: July 20, 2026 at 09:33 PM

Tile Grout Calculator

Inputs

Tiled area10 m²
Tile length30 cm
Tile width30 cm
Tile thickness8 mm
Joint width3 mm
Waste allowance10 %

This is an estimate based on the joint-volume method and a typical cementitious grout density. Actual coverage varies by grout brand, the exact density of the mixed product, tile layout, and how fully the joints are packed. Use the coverage chart on the grout bag as the final reference and buy a little extra to allow for a single dye lot.

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Construction & DIY

Tile Grout Calculator

Estimate how much grout a tiling job needs from the tiled area, tile size, joint width, and tile thickness, with a waste allowance.

Inputs

≥ 0 m²
≥ 0.1 cm
≥ 0.1 cm
≥ 1 mm
≥ 0.1 mm
%
0 – 50 %

Results

Enter a value to see results.

Details

Tiling 10 m² with 30 cm × 30 cm tiles and 3 mm joints needs about ... of grout (... of joint volume, including 10 % waste).

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Tile Grout

Grout is the material that fills the gaps between tiles, and the amount a job needs is set by four things: the tiled area, the size of each tile, the width of the joints between them, and the thickness of the tiles. This calculator estimates the grout volume and the dry weight to buy so you can avoid both running short mid-job and over-buying several bags.

The joint-volume method

Grout occupies the rectangular channels around every tile. For a field of identically sized tiles, the volume of grout per unit of tiled area works out to a simple expression:

Vper area=l+wl⋅w j⋅t\begin{aligned} V_{\text{per area}} &= \frac{l + w}{l \cdot w}\, j \cdot t \end{aligned}

where ll and ww are the tile length and width, jj is the joint width, and tt is the tile thickness. Multiplying by the tiled area AA gives the total joint volume, and multiplying by the grout density (about 1600 kg/m³ for cementitious grout) converts that volume into the dry weight you actually purchase.

The formula shows why small tiles use far more grout than large ones: mosaic and small-format tiles pack many more joints into the same area, so the l+wl⋅w\frac{l+w}{l \cdot w} term grows quickly as tiles shrink.

Worked example

Consider 10 m² of 30 × 30 cm porcelain tiles, 8 mm thick, set with 3 mm joints:

V=10⋅0.30+0.300.30⋅0.30⋅0.003⋅0.008=10⋅6.667⋅0.003⋅0.008=0.0016 m3=1.6 L\begin{aligned} V &= 10 \cdot \frac{0.30 + 0.30}{0.30 \cdot 0.30} \cdot 0.003 \cdot 0.008 \\ &= 10 \cdot 6.667 \cdot 0.003 \cdot 0.008 \\ &= 0.0016 \ \text{m}^3 = 1.6 \ \text{L} \end{aligned}

At 1600 kg/m³ with a 10% waste allowance, that is about 2.8 kg of dry grout — roughly one small bag, with a little to spare.

Consider 100 sq ft (14400 in²) of 12 × 12 in porcelain tiles, 0.3 in thick, set with 1/8 in joints:

V=14400⋅12+1212⋅12⋅0.125⋅0.3=14400⋅0.1667⋅0.125⋅0.3=90 in3≈50 fl oz\begin{aligned} V &= 14400 \cdot \frac{12 + 12}{12 \cdot 12} \cdot 0.125 \cdot 0.3 \\ &= 14400 \cdot 0.1667 \cdot 0.125 \cdot 0.3 \\ &= 90 \ \text{in}^3 \approx 50 \ \text{fl oz} \end{aligned}

At the density of cementitious grout, with a 10% waste allowance, that works out to roughly 5.7 lb of dry grout — about one small bag, with a little to spare.

Choosing inputs

The joint width is the input most people underestimate. Rectified porcelain can be laid with 2 mm1/16 in joints, while rustic, handmade, or natural-stone tiles usually need 4–5 mm3/16 in to absorb size variation, and that difference can double the grout required. Always check the coverage chart printed on the grout bag, since the exact density of the mixed product varies by brand, and buy from a single dye lot so the colour stays consistent across the whole surface.

For working out how many tiles to buy in the first place, see Tile Calculator.

Frequently Asked Questions (FAQ)

How much grout do I need?

Grout quantity depends on the tiled area, the tile size, the joint width, and the tile thickness. Smaller tiles and wider joints create more joint volume and need more grout. As a worked example, 10 m² of 30 × 30 cm tiles that are 8 mm thick with 3 mm joints holds roughly 1.6 litres of grout, which is about 2.8 kg of dry cementitious grout once a 10% waste allowance is added.

Grout quantity depends on the tiled area, the tile size, the joint width, and the tile thickness. Smaller tiles and wider joints create more joint volume and need more grout. As a worked example, 108 sq ft of 12 × 12 in tiles that are 0.3 in thick with 1/8 in joints holds roughly 50 fl oz of grout, which is about 5.7 lb of dry cementitious grout once a 10% waste allowance is added.

Why does the joint width change the amount so much?

Grout fills the gaps between tiles, so the amount scales directly with the joint width. Doubling the joint from 3 mm to 6 mm roughly doubles the grout needed for the same tiles. Joint width also depends on tile type: rectified porcelain can use 2 mm joints, while rustic or handmade tiles often need 5 mm or more to absorb size variation.

Grout fills the gaps between tiles, so the amount scales directly with the joint width. Doubling the joint from 1/8 in to 1/4 in roughly doubles the grout needed for the same tiles. Joint width also depends on tile type: rectified porcelain can use 1/16 in joints, while rustic or handmade tiles often need 3/16 in or more to absorb size variation.

What is the difference between sanded and unsanded grout?

Sanded grout contains fine aggregate and is used for joints wider than about 3 mm, where it resists shrinkage and cracking. Unsanded grout is smoother and is used for narrow joints (under 3 mm) and on polished or easily scratched tiles such as glass or marble. Both are estimated by the same joint-volume method; only the product choice differs. Always confirm against the coverage table printed on the bag.

Sanded grout contains fine aggregate and is used for joints wider than about 1/8 in, where it resists shrinkage and cracking. Unsanded grout is smoother and is used for narrow joints (under 1/8 in) and on polished or easily scratched tiles such as glass or marble. Both are estimated by the same joint-volume method; only the product choice differs. Always confirm against the coverage table printed on the bag.

Disclaimer

This is an estimate based on the joint-volume method and a typical cementitious grout density. Actual coverage varies by grout brand, the exact density of the mixed product, tile layout, and how fully the joints are packed. Use the coverage chart on the grout bag as the final reference and buy a little extra to allow for a single dye lot.

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