How to use the grout calculator
- Enter the tiled area in square feet and the tile length and width in inches.
- Enter the joint width and the joint depth, which is usually the tile thickness. Fractions of an inch are decimals, so 1/8 is 0.125 and 3/8 is 0.375.
- Set the grout density and a waste percent, then optionally the bag size.
- Read the pounds of grout, with and without waste, and the number of bags.
Formula
Cell area = (tile length + joint) x (tile width + joint)
Joint area per cell = joint x (length + width + joint)
Tiles = area x 144 / cell area
Volume = tiles x joint area per cell x depth
Pounds = volume in cubic feet x density
Volume in cubic inches is divided by 1,728 to get cubic feet. Waste is added on top.
100 square feet of 12 inch tile
Take 100 square feet of 12 by 12 inch tile with 1/8 inch joints and a joint depth of 3/8 inch. A cell is 12.125 inches square, so there are 97.9 tiles and the joints hold 110.77 cubic inches, which is 0.0641 cubic feet. At an example density of 100 pounds per cubic foot that is 6.41 pounds.
With 10% for waste the figure is 7.05 pounds, shown as 7.1 pounds, which is one 10 pound bag. Doubling the joint width to 1/4 inch raises the grout to 12.62 pounds before waste.
How the volume is found
The grout in a floor is only the fill between tiles, so the quantity depends on the joint, not on the tile alone. Small tiles have far more joint per square foot than large ones, and wider or deeper joints use more grout. This tool measures the actual joint volume instead of using a flat coverage figure.
For the tile count itself, use the tile calculator, and for the floor area use the square footage calculator.
Why density and waste are inputs
Mixed grout is denser than powder and its weight per cubic foot differs by product, so the density is a number you set, with 100 as a starting example. If the maker of your grout publishes a coverage chart, compare it with this result and trust the chart for that product.
Joints are rarely filled exactly to the full depth, and uneven or rough tile takes more. Waste covers spills and leftover mix. Other fill materials, such as epoxy, are measured with the epoxy calculator.
Assumptions and limits
- Density (100 lb per cubic foot) and waste (10%) are example values you can change.
- Joint depth is assumed equal to the number you enter. A thinner fill uses less.
- Rounded edges, bevels, hand made tile and uneven surfaces change the real quantity.
- Bags are rounded up to whole bags of the size you enter.
Frequently asked questions
How much grout do I need for 100 square feet of tile?
It depends on tile size, joint width and depth. For 12 inch tile with 1/8 inch joints that are 3/8 inch deep, about 6.4 pounds fill the joints before waste.
Do smaller tiles need more grout?
Yes. Smaller tiles mean more joints in the same area, so the same area needs more grout.
What joint depth should I use?
Use the tile thickness if the joint is filled to the bottom. If part of the depth is taken up by something else, enter the depth that grout will actually fill.
How do I turn 3/8 inch into a decimal?
Divide 3 by 8 to get 0.375. In the same way 1/8 is 0.125 and 1/4 is 0.25.