Grout Calculator

1. Enter the area you will tile, in sq ft or m2.
2. Enter the tile length, width and thickness. Measure a real tile, because the box size is often rounded.
3. Enter the joint width, or tap a joint chip such as 1/8 in. The joint must be smaller than the tile.
4. Set the waste percent and your bag size. The result shows total weight, bags to buy and the working.
5. Only change the density if your grout maker lists one. The bag chart is always the final word.

For example, the default 12 x 12 in tile, 3/8 in thick, with 1/8 in joints over 100 sq ft needs 7.69 lb of grout. With 10% waste that is 8.46 lb, so one 25 lb bag is enough.

Grout fills the gaps between tiles. So the amount you need is the volume of those gaps. Picture each tile with half a joint on every side. That makes a repeating cell.

Here L and W are the tile length and width, T is the tile thickness and J is the joint width, all in inches. The grout strip in one cell is J wide and T deep. It runs along one long side, one short side and the small square where joints cross.

There are 144 square inches in a square foot and 1728 cubic inches in a cubic foot. The formula assumes joints are filled to the full tile depth.

Smaller tiles mean more joints in every square foot. Wider joints make each of those joints hold more. Both effects stack up fast.

This table shows pounds of grout per 100 sq ft. Every row uses 3/8 in thick tile, an assumed 120 lb/ft3 and no waste, so only size and joint width change.

Doubling the joint from 1/8 in to 1/4 in about doubles the grout for 12 x 12 in tile, from 7.69 lb to 15.15 lb. Going from 12 x 12 in tile to 2 x 2 in mosaic at 1/8 in raises it from 7.69 lb to 42.82 lb.

The Tile Council of North America (TCNA) gives a simple rule for cement grout. Joints smaller than 1/8 in generally take unsanded grout. Joints 1/8 in and wider take sanded grout.

A 3 mm joint is just under 1/8 in (3.175 mm), so it sits right at the line. In that case, read the joint range printed on the bag. The calculator shows this guidance under your result.

Sanded or not, the joint volume is the same. The type of grout changes the weight per volume, not the size of the gaps.

Yes. Tile grouts come in several types. A U.S. Department of Veterans Affairs tiling specification lists standard cement grout (ANSI A118.6), high performance cement grout (ANSI A118.7), water-cleanable epoxy grout (ANSI A118.3) and modified epoxy emulsion grout (ANSI A118.8).

Epoxy and urethane grouts are often sold in kits or tubs by volume, not in powder bags by weight. Their density is not the same as cement grout.

The joint volume from this calculator still applies to any grout. Compare it with the volume a kit fills, or use the coverage chart on the package. If the maker lists a density, enter it in the advanced box.

Say you tile 100 sq ft with 12 x 24 in porcelain that is 3/8 in thick, with 1/8 in joints. You add 10% waste and buy 10 lb bags.

1. Cell area = (12 + 0.125) x (24 + 0.125) = 292.5156 sq in.
2. Grout per cell = 0.125 x 0.375 x (12 + 24 + 0.125) = 1.6934 cu in.
3. Per sq ft = 1.6934 / 292.5156 x 144 = 0.8336 cu in.
4. For 100 sq ft = 83.4 cu in, which is 0.0482 cu ft.
5. Weight = 83.4 / 1728 x 120 = 5.79 lb. With 10% waste: 6.37 lb.
6. Bags = 6.37 / 10 = 0.64, rounded up to 1 bag.

Large tiles need little grout. Here one small bag covers the job, with room to spare.

1. Using the Nominal Tile Size

A tile sold as 12 x 12 in may measure a little less. Measure one tile with a tape and use that size.

2. Forgetting Tile Thickness

Grout volume grows with depth. A 3/8 in tile holds 50% more grout per foot of joint than a 1/4 in tile.

3. Mixing Up Inches and Millimeters

A 3 mm joint is about 0.118 in, not 3 in. Pick the right unit next to each box. The calculator converts your numbers when you switch a unit.

4. Trusting the Density Over the Bag

The 120 lb/ft3 default is an assumption for estimates. Real products vary, so the coverage chart on the bag wins.

It depends on tile size, tile thickness and joint width. For 12 x 12 in tile that is 3/8 in thick, with 1/8 in joints, 100 sq ft needs about 110.8 cubic inches of grout. At an assumed 120 lb/ft3, that is about 7.69 lb, or 8.46 lb with 10 percent waste. The same area of 12 x 24 in tile needs about 5.79 lb before waste.

Each tile and its share of joint forms a cell of (L + J) x (W + J). The grout in one cell is J x T x (L + W + J), where J is joint width and T is tile thickness. Divide by the cell area and multiply by 144 to get cubic inches per sq ft. Multiply by your area, then divide by 1728 and multiply by the density to get pounds.

For cement grout, the Tile Council of North America says joints < 1/8 in generally take unsanded grout, and joints 1/8 in and wider take sanded grout. A 3 mm joint is just under 1/8 in, so check the joint range printed on the bag. Always follow the tile maker's advice too.

Small tiles mean many more joints in each square foot. With 1/4 in thick tile and 1/8 in joints, 2 x 2 in mosaic needs about 4.11 cubic inches of grout per sq ft. With the same joints, 12 x 12 in tile that is 3/8 in thick needs only about 1.11 cubic inches per sq ft, even though it is thicker.

This calculator starts at 10 percent. Some grout is always lost in the bucket, on the float and during cleanup. Add more if your tile edges are rounded or uneven, or if joint widths vary. Grout is sold in whole bags, so you will often have some left over anyway.

The joint volume is the same for any grout, so the cubic inches and liters still apply. The weight does not, because epoxy and urethane grouts have a different density and are often sold in kits or by volume. Use the coverage chart on the package, or enter the maker's density in the advanced box.

It depends on your tile and joints. At an assumed 120 lb/ft3, a 25 lb bag covers about 325 sq ft of 12 x 12 x 3/8 in tile with 1/8 in joints, before waste. With 2 x 2 in mosaic that is 1/4 in thick and has 1/8 in joints, it covers only about 88 sq ft. The chart on the bag is the better guide.

• Tile Council of North America: Grout FAQ (unsanded grout for cement grout joints under 1/8 in, sanded for 1/8 in and larger).
• U.S. Department of Veterans Affairs, Master Specification Section 09 30 13: Ceramic/Porcelain Tiling (via WBDG) (grout types by ANSI A118.3, A118.6, A118.7 and A118.8).
• NIST Special Publication 811, Appendix B.8: Factors for Units Listed Alphabetically (inch, square foot, cubic inch, pound and pound per cubic foot conversions).