About the Grout Calculator
This grout calculator estimates how much grout a tiling project needs from the dimensions that actually drive it: the tile length and width, the tile thickness (joint depth), the grout joint width and the total area. It returns the pounds of grout, the number of bags to buy and how many square feet a bag will cover for your layout.
Small tiles and wide joints use far more grout than large-format tile with tight joints — a mosaic backsplash can need several times as much grout per square foot as a 24-inch porcelain floor. Use this before buying so you get one consistent batch (color can vary between lots) without paying for bags you will not open.
The result assumes joints are filled to the full tile thickness and uses a typical mixed cement-grout density of about 110 lb per cubic foot, which you can change. Epoxy and urethane grouts are sold by volume or unit size, so compare the cubic-feet figure in the notes with the product’s stated yield.
With the default inputs, the grout needed (with waste) is 7.8 lb. Change any value above to recalculate instantly.
How to use the grout calculator
- 1Measure the tiled area in square feet (walls and floors separately if tiles differ).
- 2Enter the tile length, width and thickness in inches.
- 3Enter the joint width you will use — check your spacers.
- 4Choose the bag size you plan to buy and keep the default density unless your product states one.
- 5Buy the number of bags shown, all from the same lot for consistent color.
Formula and method
Each tile plus its share of joint occupies a module of (L + J) × (W + J) square inches. Within that module the grout fills one joint along the length and one along the width, which is (L + W + J) × J square inches of joint, filled to the tile thickness T. Dividing 144 sq in by the module area gives the number of modules per square foot, so the formula returns the cubic inches of grout in every square foot of tile.
Cubic inches are converted to pounds with the mixed grout density (lb per cubic foot ÷ 1,728 cubic inches per cubic foot), multiplied by the area, and a waste allowance is added for mixing leftovers and cleanup. Bags are rounded up to whole bags.
- L, W
- Tile length and width (in)
- T
- Tile thickness = joint depth (in)
- J
- Grout joint width (in)
- density
- Mixed grout density (lb/ft³)
Worked examples
100 sq ft of 12 × 12 tile, 3/8 in thick, 1/8 in joints
Each square foot has about 1.11 cubic inches of joint, which is 0.071 lb of grout at 110 lb/ft³. Over 100 sq ft with 10% waste that is about 7.8 lb — a single 25 lb bag, which would cover roughly 322 sq ft of this layout.
200 sq ft of 3 × 6 subway tile, 1/16 in joints, 10 lb bags
Subway tile has many joints per square foot, so even with thin 1/16-inch joints it uses about 0.087 lb per sq ft. For 200 sq ft plus 10% that is 19.2 lb, or two 10 lb bags.
500 sq ft floor, 12 × 12 tile with wide 1/4 in joints
Doubling the joint width to 1/4 inch almost doubles grout use to 0.139 lb per sq ft. Across 500 sq ft plus waste you need about 76 lb — four 25 lb bags.
Frequently asked questions
How much grout do I need per square foot?+
It depends on tile size, thickness and joint width. 12 × 12 tile with 1/8-inch joints uses roughly 0.07 lb per sq ft, while small mosaics or 1/4-inch joints can use two to four times as much.
How many square feet does a 25 lb bag of grout cover?+
Anywhere from under 100 sq ft for mosaics with wide joints to 400+ sq ft for large-format tile with narrow joints. For 12 × 12 tile, 3/8 inch thick with 1/8-inch joints, it is roughly 320 sq ft.
Should I use sanded or unsanded grout?+
Unsanded grout is generally used for joints of 1/8 inch or less and on easily scratched surfaces; sanded grout is used for wider joints because the sand resists shrinkage and cracking. Always follow the grout manufacturer’s joint-width range.
Why do I need extra grout?+
Some grout is lost in the bucket, on the float and during sponge cleanup, and some joints end up deeper than planned. A 10% allowance covers this, and buying all bags from one lot avoids color differences.
Does tile thickness affect grout quantity?+
Yes. Joints are filled to roughly the full tile thickness, so a 1/2-inch tile uses a third more grout than a 3/8-inch tile with the same size and joint width.