EstimatorKitFree grout calculator
Grout by the joint, in pounds and bags
Enter the tiled area, the size of the tile and the width and depth of the joint, and this returns the pounds of grout, the bags that rounds to, and whether that width takes sanded or unsanded. The tile size is an input because it sets how much joint a square foot has: at a 1/8 in joint and 1/4 in depth, 100 sq ft of 24 in tile needs 3.8 lb, and the same 100 sq ft laid in 2 in mosaic needs 45.3.
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- Sanded or unsanded
- Joint run in linear feet
- Sealer figured too
The tile is here to set how much joint there is per square foot. Nothing on this page counts tiles.
Sanded, because the joint is 0.125 in or wider
1 × 25 lb bag
- Grout needed
- 10.2 lb
- One bag covers
- 294 sq ft
- Left in the last bag
- 14.8 lb
- Joint to fill
- 180 linear ft
Bare joint against the bag figure
- Joint volume, 0.84 cu in per sq ft
- 0.059 cu ft
- That volume cured, at 125 lb per cu ft
- 7.32 lb
- Powder the coverage formula asks for
- 10.2 lb
The bag figure runs 1.39 times the cured weight of the holes you are filling. That margin is not an error — the constant in the coverage formula printed on cementitious grout bags and in the manufacturers' own estimating sheets — and it exists because the bucket, the float and the sponge all take a share, and because finishing a floor out of a second lot shows.
At 0.125 in the joint needs the sand: it is aggregate, and without it a cement grout this wide shrinks away from the tile edge and cracks along the middle of the run. On polished marble or glass, ask for a non-sanded high-performance grout instead — the sand scratches both.
Sealing that run takes about 7.2 fl oz of penetrating sealer — 1 applicator — scaled from grout sealer applicators state 150 to 250 linear feet per 8 fl oz bottle at a 1/8 in joint. Cementitious grout wants 48 to 72 hours to cure before any of it goes on; epoxy grout wants none of it ever.
How to work out how much grout to buy
Three inputs, and the tile is only there to describe the joint.
Give the area that is already tiled
Type the square footage straight in, or switch to length by width if that is how it was measured. Walls and floor go in together when they are being grouted out of the same bucket, and there is no tile count anywhere on this page — a hundred square feet is a hundred square feet whether it arrived as four slabs or four hundred mosaics.
Describe the joint: the tile that forms it, its width and its depth
The tile dimensions set how much joint exists per square foot, which is the number this whole calculation turns on. Width is what the spacers hold. Depth is the tile thickness minus whatever mortar squeezed up during setting — 5/16 in for glazed wall tile, 3/8 in for most floor tile, 1/2 in for large-format porcelain, and less than any of those if the trowel ridges came most of the way up.
Read the bags, and check the two weights against each other
The result gives pounds, whole bags at 25 or 10 lb, what one bag covers at this joint, and the run of joint in linear feet for the sealer. Underneath it the geometric volume of the joints sits next to the pounds the coverage formula asks for, so the cushion in that formula is visible as a ratio rather than buried inside a single number.
Technical specifications
| Coverage formula | ((tile L + tile W) ÷ (tile L × tile W)) × joint width × joint depth × 14.5 = lb per sq ft, all dimensions in inches |
|---|---|
| Sanded threshold | 1/8 in — unsanded below it, sanded at and above; over 1/2 in needs a wide-joint or epoxy product |
| Joint depth guidance | 5/16 in glazed wall tile, 3/8 in floor tile, 1/2 in large-format porcelain, less any mortar in the joint |
| Bag weights | 25 lb and 10 lb preset, or any weight typed in |
| Cushion made visible | The bag figure runs 1.39× the cured weight of the joint volume, and both are printed |
| Sealer coverage | 200 linear feet of 1/8 in joint per 8 fl oz applicator, scaled inversely with joint width |
| Cure before sealing | 48 to 72 hours for cementitious grout; epoxy grout takes no sealer at all |
Frequently asked questions
How much grout do I need for 100 square feet?
Anywhere between about 4 lb and about 45 lb, and the tile decides which. Hold the joint at 1/8 in wide and 1/4 in deep and vary only the tile: 24 in slabs take 3.8 lb over that hundred square feet, 12 in tile takes 7.6, 3 by 6 in subway takes 22.7, and 2 in mosaic takes 45.3. That twelvefold spread is why 'grout for 100 sq ft' has no answer without the tile size, and why every chart on the back of a bag is indexed by tile size first.
Should I use sanded or unsanded grout?
Unsanded below a 1/8 in joint, sanded at 1/8 in and above. The sand is aggregate: it holds the volume of the joint against the shrinkage that happens as the cement cures, and without it a wide joint pulls away from the tile edge and splits down the middle. Below 1/8 in the grain simply cannot pack into the gap, so the unsanded formula takes over. Two exceptions are worth knowing — sand scratches polished marble and glass tile, and the single-component high-performance grouts written to ANSI A118.7 are rated from 1/16 in right up to 1/2 in in one product.
How deep is a grout joint?
As deep as the tile is thick, less whatever mortar came up under it. That is the input most calculators skip and it moves the answer proportionally: the same floor at a 1/4 in effective depth takes a third less grout than at 3/8 in. If the setter used a large notch and the ridges collapsed most of the way up the tile edge, measure it — scrape a joint before grouting and you will often find half the depth you assumed, which is a bag you did not need.
Does grout have to be sealed?
Cementitious grout does; epoxy grout does not and cannot. A penetrating sealer soaks into the pores of a cement joint and slows the rate at which coffee, wine and mop water get in — it is not a film and it does not make grout waterproof. Wait 48 to 72 hours after grouting so the cement has cured before the sealer goes on. Epoxy grout, written to ANSI A118.3, is a resin with no capillary pores at all, so a sealer sits on top of it doing nothing until it wears off.
Why does grout crack in a straight line along a joint?
Almost always because that joint was doing a job grout cannot do: absorbing movement. Anywhere the tile turns a corner, meets a different material, runs into a wall or crosses a slab joint, the assembly moves and rigid cement cannot follow it — the TCNA detail EJ171 puts a flexible sealant in those positions for exactly this reason. The other two causes are a much shorter list: too much water in the mix, which dilutes the cement and leaves a powdery joint, and grouting over a mortar bed that had not cured, which pulls water out of the grout from below.
Can I grout the corner where the wall meets the floor?
No — that is a change of plane and it takes a color-matched silicone or urethane sealant instead. Every grout manufacturer sells caulk tinted to match each of its grout colors precisely because this joint, the perimeter against the tub, and the inside corners of a shower are all movement joints. Grout them and they crack within a season; caulk them and the wall can move against the floor the way buildings actually do.
How long after setting tile can I grout?
24 hours for a standard thinset bed under normal tile, longer for anything the mortar cannot dry out from underneath. Large-format porcelain over a non-porous substrate is the usual culprit: the tile is impervious, the substrate is impervious, and the only escape route for the water in the mortar is the open joint you are about to fill. Give that assembly 48 to 72 hours. Mastic behind wall tile in a wet area needs longer again, and is the wrong adhesive there anyway.
About grout coverage, and why the tile size is the input that matters
Grout is bought by weight and consumed by volume, and the volume is a perimeter quantity. Every tile contributes half of the joint on each of its edges, so the run of joint in a square foot is set by the ratio of a tile’s perimeter to its area — a ratio that climbs steeply as the tile gets smaller. That is the entire reason the published coverage formula divides the sum of the tile’s two dimensions by their product before it touches the joint at all. Hold the joint at 1/8 in wide and 1/4 in deep and the arithmetic is stark: 24 in tile puts 1 linear foot of joint in a square foot, 12 in tile puts 2, and 2 in mosaic puts 12. A floor tiled in mosaic takes twelve times the grout of the same floor in slabs, which is why a bag-count guess that starts from square footage is not a guess at all. Counting the tile itself is a different question with a different answer, and it lives on the tile calculator.
The width of that joint then decides which product fills it. Sand in grout is aggregate, doing what aggregate does in concrete: holding the volume against the shrinkage that comes with curing cement. Above about 1/8 in an unsanded mix has too much paste and too little to hold it, so it pulls away from the tile edges and cracks down the center of the run. Below 1/8 in the grain will not pack into the gap, and forcing it leaves voids behind a joint that looks filled. That is the whole of the sanded rule, and it explains its own exceptions: polished marble and glass get scratched by the sand, so they take an unsanded or a high-performance grout regardless of width, and the single-component grouts written to ANSI A118.7 span 1/16 in to 1/2 in in one bag because their aggregate is engineered rather than quarried.
What no grout can do is move. The tile field, the substrate and the building all expand and contract at different rates, and the industry answer — TCNA detail EJ171 — is to leave the corners, the perimeter, the tub line and any joint over a structural break to a flexible sealant, which every manufacturer sells tinted to match its own grout colors. Filling those with cement is what puts a hairline crack in a bathroom during its first year more often than anything else does, and no amount of extra grout in the order prevents it. Once the field joints have cured for two or three days, a penetrating sealer slows staining without ever making the joint waterproof; on epoxy it is wasted, because there are no pores for it to enter. Where the same bathroom gets a plank floor outside the shower, the flooring calculator handles the transition, and the walls that meet this tile are usually being ordered in the same trip on the drywall calculator.
Where the joint dimensions you typed go
Every number on this page is worked out by JavaScript running in the tab you are reading it in. Nothing you type — measurements, quantities, the prices your supplier quoted you — is uploaded, logged or kept, which is also why the calculators carry on working on a site with no signal.
That includes the coverage formula itself, which runs here rather than on a server: there is no lookup request behind the bag count and nothing to intercept.