Tile Grout Calculator
Calculate grout from your tile size, joint width and tile thickness — pounds of sanded or unsanded grout and the bags to buy.
How grout is figured
Grout fills a network of channels, and the trade calculates it the honest geometric way: the total joint volume in the floor. Each tile sits in a cell of tile-plus-joint; the joint's share of that cell, times the tile's thickness (the joint depth), times the whole area, is the volume to fill. Weight comes from the grout's density — about 0.069 lb per cubic inch for sanded grout, 0.05 for unsanded.
Grout volume = area × joint share of each tile cell × tile thickness · Weight = volume × density
Example: a 20 × 10 ft floor in 12 × 12 in tile with 1/8 in joints and 3/8 in thickness needs about 15.4 lb of sanded grout exactly — call it one 25-lb bag with working room, which is why a single bag covers roughly 325 sq ft of this tile.
Sanded or unsanded?
| Joint width | Grout | Sold as |
|---|
| Under 1/8 in | Unsanded — fine, smooth, safe on polished stone and glass | 10-lb boxes |
| 1/8 in and wider | Sanded — the sand stops shrinkage cracks in wide joints | 25-lb bags |
Small tiles drink grout: a 2 × 2 mosaic has six times the joint length of a 12 × 12 floor per square foot, and the calculator's numbers will show it. Whatever the size, check the chart on your specific bag before a big floor — brands vary a little around the standard densities used here, and their figure governs their product. Keep a small reserve from the same dye lot for future repairs; grout color is nearly impossible to match years later.
Frequently asked questions
Why does the result say pounds as well as bags?
Because many floors need less than a bag, and some need a bag and a bit. Pounds tell you the truth of the job; bags tell you what to buy. If the count lands just over a bag, a 10-lb box of the same grout often tops it up more cheaply than a second 25-lb bag.
Is the joint filled to the full tile thickness?
Very nearly — grout is struck slightly below the tile face, but installers figure volume at full depth because the joint shoulders and minor voids take up the difference. The estimate here follows that trade practice.
Can I use sanded grout on marble or glass tile?
Manufacturers say no: the sand can scratch polished and delicate surfaces even at wide joints. Unsanded (or a modern high-performance grout rated for the material) is the safe choice there, whatever the joint width.
How much grout does a shower wall need compared with a floor?
The same formula — area, tile, joint, thickness. Wall tile is usually thinner (1/4 in), which is why the thickness selector matters: a thin tile at the same size and joint needs about a third less grout than a 3/8-inch floor tile.
CalcCoverage