Grout Calculator
Grout quantity depends on far more than floor area: a small tile with a wide joint can need five times the grout of a large tile with a tight one. Enter the tile size, its thickness and your joint width to get the pounds needed, the number of bags, and whether the joint calls for sanded or unsanded grout.
Results
How much grout a job actually takes
Grout fills the space between tiles, so the quantity depends on how much of that space there is — which is a function of tile size, tile thickness and joint width, not of floor area alone. Two 100 square foot floors can differ by a factor of five. Large-format 24 × 24 in tile with a 1/16 in joint has very little perimeter per square foot; 2 × 2 in mosaic with a 1/8 in joint is nearly all perimeter.
Formula: lb per sq ft = ((tile length + tile width) ÷ (tile length × tile width)) × tile thickness × joint width × 14.5
All four measurements are in inches. The 14.5 is the constant tile manufacturers use on their published coverage charts; it folds in the density of mixed grout plus a small working allowance, so it is not a straight unit conversion and it is not the same for every brand. Treat the result as a planning figure and check the bag.
| Tile size | Coverage per 25 lb bag |
|---|---|
| 2 × 2 in mosaic | ≈ 37 sq ft |
| 4 × 4 in | ≈ 74 sq ft |
| 6 × 6 in | ≈ 110 sq ft |
| 12 × 12 in | ≈ 221 sq ft |
| 12 × 24 in | ≈ 294 sq ft |
| 24 × 24 in | ≈ 441 sq ft |
Sanded, unsanded or epoxy
The joint width picks the grout, not the other way round:
| Type | Joint width | Where it belongs |
|---|---|---|
| Unsanded | Up to 1/8 in | Wall tile, polished stone, glass — anything sand would scratch |
| Sanded | 1/8 in and wider | Floors and most wall tile; the sand stops the joint shrinking as it cures |
| Epoxy | 1/16 to 1/2 in | Showers, counters, commercial kitchens — waterproof, stain-proof, needs no sealer |
| Single-component (pre-mixed) | 1/16 to 1/2 in | Small jobs and repairs; convenient, more expensive per pound, slower to cure |
Epoxy grout is sold by volume in kits rather than by the pound, so the figure above will not translate directly — use the kit's own coverage chart. It also sets fast and is unforgiving of a slow cleanup, which is why it is a poor first grout on a large floor.
Joint width is a decision, not a default
Wider joints hide size variation between tiles. Rectified tile — cut to a precise size after firing — can take a 1/16 in joint because every piece is genuinely the same. Ordinary pressed tile varies enough that a joint under 1/8 in will telegraph every difference along the run. Natural stone varies most of all.
- 1/16 in — rectified porcelain, large format, a deliberately seamless look. Unsanded only.
- 1/8 in — the default for most floor and wall tile, and the width most coverage charts assume.
- 3/16 to 1/4 in — handmade, saltillo, slate and anything with an irregular edge.
- 3/8 to 1/2 in — rustic stone and exterior paver-style tile, where movement matters more than looks.
Wider joints also mean more grout to seal and more surface to keep clean, which is a maintenance cost rather than a material one.
Why coverage charts disagree with each other
Two manufacturers can quote coverage for the same tile size and be 20% apart. The reasons are real, not sloppy: grout formulations differ in density, some charts assume a full joint and some assume a slightly recessed one, and some quietly include a waste allowance while others quote the bare calculation. On top of that, how hard you pack the float changes the number on the actual floor.
The practical answer is to buy one bag more than the calculation says on any job over about 100 square feet, and to buy it at the same time as the rest. An unopened bag is usually returnable; a color that no longer matches is not.
Frequently asked questions
How much grout do I need for 100 square feet?
For 12 × 12 in tile that is 3/8 in thick with a 1/8 in joint, 100 square feet needs about 11.3 pounds of grout, so a single 25 lb bag covers it with room to spare. Change the tile to 2 × 2 in mosaic at the same joint and the same 100 square feet needs about 68 pounds — three bags. Tile size drives the answer far more than area does.
Should I use sanded or unsanded grout?
Joint width decides it. Joints under 1/8 in take unsanded grout, because sand cannot pack into a gap that narrow. Joints of 1/8 in and wider take sanded grout, which uses the sand as aggregate to stop the joint shrinking and cracking as it cures. At exactly 1/8 in either is rated, so choose unsanded if the tile is polished stone or glass that sand would scratch.
How many square feet does a 25 lb bag of grout cover?
It depends almost entirely on tile size. At a 1/8 in joint with 3/8 in thick tile, a 25 lb bag covers roughly 221 square feet of 12 × 12 in tile, about 74 square feet of 4 × 4 in tile, and only about 37 square feet of 2 × 2 in mosaic. Smaller tile means more joint per square foot and much more grout.
What size grout joint should I use?
One eighth of an inch is the default for most floor and wall tile. Rectified porcelain, cut precisely after firing, can go down to 1/16 in. Handmade, slate and natural stone need 3/16 to 1/4 in because the pieces vary in size and a narrow joint would show every difference.
Can I use sanded grout on glass or polished marble?
No. The sand will scratch a polished or soft surface as you work the float across it, and the damage shows immediately under raking light. Use unsanded or epoxy grout on glass, polished marble, and any honed stone, and keep the joint at 1/8 in or under so the unsanded grout is within its rating.
Does grout need to be sealed?
Cement-based grout, sanded and unsanded alike, is porous and should be sealed once it has fully cured — usually 48 to 72 hours, though the bag will say. Epoxy grout does not need sealing at all, which is a large part of why it costs more. Sealing is not permanent; wet areas typically want it redone every year or two.