YepCalc

Grout Calculator

Find how much cement grout you need for a tile floor, wall, or backsplash, by weight and in bags. Enter the area, the tile size and thickness, and the grout joint.

Section 1

Add floors or walls, or subtract areas that need no grout, such as a window or a tub.

Tile and joint size

Use the actual size on the box, which can be slightly smaller than the nominal size.

Use the thickness on the box or spec sheet.

1/8 in (3 mm) is a common minimum. Use the joint your tile maker recommends.

Leave blank to fill the joints to the full tile thickness.

Grout density

Typical cement grout: 112.4 lb/ft³

Waste, bags, and cost

%

Recommended for grout: 10%

For a bag or box not listed, enter the weight printed on it.

per

Result

Enter the dimensions of a floor or wall to see the grout you need.

How much grout you need

Grout fills the joints between tiles, so the amount depends on the joint width and depth and on how many joints there are per square foot. Each tile shares the joints around it with its neighbors, so one tile and its share of the joints cover (tile length + joint) × (tile width + joint). The calculator finds the grout per unit of area as:

Grout per area = joint width × (tile length + tile width + joint width) × joint depth ÷ ((tile length + joint width) × (tile width + joint width))

Grout volume = net area × grout per area × (1 + waste % ÷ 100)

Grout weight = grout volume × density

Bags = grout weight ÷ weight per bag, rounded up

Convert every measurement to the same unit before you multiply. The joint depth is the tile thickness unless you enter a smaller depth. With several sections, the calculator adds the sections set to Add and subtracts those set to Subtract. For shapes other than rectangles, it uses these formulas:

Shape Area
Rectangle length × width
Circle π × diameter² ÷ 4 (or π × radius²)
Triangle (base and height) base × height ÷ 2
Triangle (three sides) Heron's formula: √(s(s − a)(s − b)(s − c)), where s = (a + b + c) ÷ 2
Trapezoid (parallel side A + parallel side B) ÷ 2 × height
Ring π × (outer diameter² − inner diameter²) ÷ 4
Rectangular border outer length × outer width − (outer length − 2 × border width) × (outer width − 2 × border width)
Known area the area you enter

Some manufacturers use a shorter formula, (tile length + tile width) ÷ (tile length × tile width) × joint width × depth. It counts the tiles without their joints, so it gives more grout than the formula above: about 1.6% more for 12 in tiles with 1/8 in joints, 9.5% more for 2 in mosaics, and 19% more for 1 in mosaics.

Grout density

Grout is sold by weight, so turning the volume of the joints into pounds or kilograms needs a density. The calculator uses 112.4 lb/ft³, 1,800 kg/m³, 1.8 t/m³. That's the weight of dry grout powder it takes to fill a cubic foot or cubic meter of joints once it's mixed with water, not the density of the loose powder in the bag.

The value comes from manufacturers' coverage charts. With the formula above, the chart for Custom Building Products' Polyblend Plus Sanded Grout works out to about 112 lb/ft³ for 12 in to 24 in tiles with 1/8 in to 1/4 in joints. Laticrete's data sheet for 1500 Sanded Grout (Middle East edition) matches the shorter formula with 1.8 kg per liter of joint.

Charts differ between brands. For tiles 12 in and larger, Mapei's Keracolor S chart covers about 10% more area per bag, close to 1.6 t/m³. For mosaics and joints that are wide compared with the tile, some charts call for 10% to 40% more grout than this calculator. Check the coverage chart of the grout you buy. If it calls for more, raise the waste allowance or enter a different density.

Unsanded grout is for joints up to 1/8 in (3 mm), and sanded grout for joints from 1/8 in to 1/2 in (3.1 to 12.7 mm), according to Custom Building Products' data sheets. The same maker's chart for unsanded grout works out to about 5% lighter than its sanded grout, smaller than the difference between brands, so the calculator uses one density for both. Choose the type that fits your joint width from the product label.

How much area a bag of grout covers

These areas come from the calculator's own formula, a density of 112.4 lb/ft³ (1.8 t/m³), no waste allowance, and joints filled to the full tile thickness. Tiles are listed as length × width × thickness. The areas are not copied from manufacturers' charts, and your product's chart may differ, especially for mosaics.

Square feet covered by a 25 lb bag

Tile (in) Joint width (in)
1/83/161/4
18 × 18 × 3/8 517.9347.1261.6
12 × 24 × 3/8 461.2309.3233.4
12 × 12 × 3/8 347.1233.2176.2
6 × 6 × 1/4 264.3178.9136.2
3 × 6 × 1/4 179.2122.393.8
2 × 2 × 1/4 93.565.150.9
1 × 1 × 1/4 50.936.729.7

Square meters covered by a 5 kg bag

Tile (mm) Joint width (mm)
235
600 × 600 × 10 41.928.016.9
300 × 600 × 10 28.018.711.3
300 × 300 × 8 26.317.610.7
100 × 100 × 6 11.98.15.0
25 × 25 × 4 4.93.42.3

To include waste, divide the area by 1 plus the waste allowance. With 10%, a bag covers the area in the table ÷ 1.1.

Joint width and depth

The amount of grout grows with the joint width. With 12 in × 12 in × 3/8 in tiles, a 5/32 in joint takes about 25% more grout than a 1/8 in joint. Custom Building Products' technical bulletin TB89 makes the same point: a 1/32 in difference changes the grout needed by about 25%. Measure the joint you'll actually leave, or use the spacer size.

TB89 also recommends filling grout joints at least 2/3 full. If the thinset fills the bottom of the joints, enter the depth left for grout as the Joint depth. Leaving it blank fills the joints to the full tile thickness, which gives a little more grout than you may need.

For mosaic tiles on sheets, enter the size of one piece as the tile size. The grout also fills the joints between the pieces on each sheet, so entering the whole sheet as one tile would leave you short.

How much extra grout to buy

The calculator adds 10% for waste, spillage, and cleanup, as Laticrete's project estimator recommends. Laticrete adds another 10% to 15% for unglazed quarry tile. Textured or porous tiles also hold grout on their surface, so raise the waste allowance for them as well.

Grout bag sizes

Grout is sold in bags and boxes labeled by weight, in the US as well as in metric countries, so the calculator counts bags by weight. The 10 lb and 7 lb sizes are often boxes; count them the same way. The calculator shows these sizes:

Bag Examples
25 lb Custom Building Products Polyblend Plus, Mapei Keracolor S, Laticrete 1500 and 1600
10 lb Custom Building Products Polyblend Plus Non-Sanded (box), Laticrete PERMACOLOR Select
7 lb Custom Building Products Polyblend Plus Sanded (box)
20 kg Ardex FG 8 (New Zealand)
10 kg Laticrete 1500 Sanded Grout (Middle East)
5 kg Ardex FG 8, Laticrete 1500 Sanded Grout, Mapei Keracolor FF (UK)

For another size, such as an 8 lb carton or a 25 kg bag, enter its weight in Custom bag size.

Examples

A bathroom floor

A floor 10 ft × 12 ft is 120 ft². With 12 in × 12 in × 3/8 in tiles and 1/8 in joints, one tile's joints take 1/8 × (12 + 12 + 1/8) = 3.016 in², and one tile with its joints covers 12.125 × 12.125 = 147.02 in². So each square foot needs 144 × 3.016 × 3/8 ÷ 147.02 = 1.108 in³ of grout. For 120 ft² that's 132.9 in³, or 146.2 in³ with 10% added: 0.63 gal (2.40 L). At 112.4 lb/ft³, you need 9.5 lb (4.3 kg), so one 25 lb bag is enough.

The same floor with mosaics

With 2 in × 2 in × 1/4 in mosaic tiles and 1/8 in joints, the same floor needs 35.3 lb (16.0 kg), about 3.7 times as much, even though the tiles are thinner. That's 2 bags of 25 lb.

Metric dimensions

A floor 5 m × 4 m is 20 m². With 600 mm × 300 mm × 10 mm tiles and 3 mm joints, each square meter needs 3 × (600 + 300 + 3) × 10 ÷ (603 × 303) = 0.148 L of grout. For 20 m² that's 2.97 L, or 3.26 L with 10% added. At 1.8 t/m³, you need 5.9 kg, so 2 bags of 5 kg or one of 10 kg.

FAQ