Calculator
Grout & Thinset Calculator
Grout and thinset are two different products with two different sizing formulas, and lumping them together is where a lot of tile-project budgets go wrong. Grout is sized by the actual volume of the joints themselves — a real, calculable volume based on tile size, joint width, and joint depth. Thinset is sized by trowel notch size, which determines how thick a bed of adhesive gets spread under the tile, not by joint volume at all.
This calculator runs both formulas side by side so you order the right amount of each, matched to your specific tile calculator order.
Calculate your quantity
sq ft per 50lb bag
lbs
Grout bags
1 25lb bags
Thinset bags
2 50lb bags
- Grout needed
- 6.5 lbs
- Tiled area
- 100 sq ft
Shopping summary
- • 1 bag(s) of grout (25lb)
- • 2 bag(s) of thinset
This is an estimate — confirm structural work with a professional.
How this calculation works
Grout volume (cubic inches) = joint width x joint depth x total joint length, where total joint length comes from the number of tiles and their perimeter. Convert to pounds using the grout manufacturer's published coverage table (sanded grout typically covers more linear joint footage per pound than unsanded, and joint width is the single biggest driver — a 1/8-inch joint uses roughly half the grout of a 1/4-inch joint on the same tile).
Thinset coverage is a completely different calculation: it's driven by trowel notch size, not tile size. A 1/4-inch square-notch trowel spreads a thinner bed than a 1/2-inch notch, and larger-format tile needs a bigger notch (and therefore more thinset per square foot) to get full contact and support across the tile's back. Manufacturer coverage charts list square-foot-per-bag figures by notch size — always check the specific bag, since formulations vary.
The formula
groutLbs = ( (area×144 / (tileL×tileW)) × (tileL+tileW) ) × jointWidth × jointDepth / 1728 × 100; thinsetBags = ceil(area / thinsetCoverage)
- (area×144 / (tileL×tileW)) × (tileL+tileW)
- Total linear inches of joint across the whole floor, derived from tile count times ONE length-plus-width per tile rather than a full perimeter per tile — every joint sits between two tiles, so counting a full 2×(L+W) perimeter for each one would double-count every shared edge.
- jointWidth × jointDepth
- The joint's cross-section in inches, not its length — width is the visible gap between tiles and depth is how far down the joint the grout actually fills, which is usually the tile's own thickness, not the full bed of thinset beneath it.
- × 100
- Grout's assumed density in pounds per cubic foot, applied after the cubic-inch volume is converted to cubic feet — this stands in for sanded grout's typical bulk density and is the reason grout is reported in pounds while thinset is reported in bags.
- thinsetCoverage
- Square feet one 50 lb bag covers at your chosen trowel notch, entered directly rather than computed — the calculator has no notch-size field, so a bigger notch for large-format tile has to be represented by lowering this number, the same way ceiling-paint texture is represented by lowering a coverage field.
Where these numbers come from
- joint length = tile count × (L + W), not tile count × 2(L + W)
- Derived on this page from the TCNA-style convention for estimating grout joint length across a tiled field: each tile is credited with one length-run and one width-run of joint, which correctly avoids counting the joint any interior tile shares with its neighbor twice.
- 100 lb per cubic foot grout density
- Trade convention for sanded cement grout used as a planning figure across manufacturers; unsanded and epoxy grout run to somewhat different real densities, so treat this as a working estimate rather than a specific product's spec sheet number.
- no trowel-notch field
- Trade convention, stated plainly rather than modeled: manufacturer coverage charts key thinset yield to notch size, and this calculator asks for that yield directly as "coverage per bag" rather than asking for a notch size and deriving it, so the number entered should already reflect the notch your tile size requires.
Worked examples
A 9 by 11 foot floor in 13 inch tile, 3/16 inch joints
| Room length | 9 ft |
|---|---|
| Room width | 11 ft |
| Tile length | 13 in |
| Tile width | 13 in |
| Joint width | 0.1875 in |
| Joint depth | 0.3125 in |
| Thinset coverage | 45 sq ft |
| Grout bag size | 20 |
| Grout bags | 1 20lb bags |
|---|---|
| Thinset bags | 3 50lb bags |
| Grout needed | 7.4 lbs |
| Tiled area | 99 sq ft |
99 sq ft of 13 inch tile needs 7.4 lbs of grout — comfortably inside one 20 lb bag with plenty left for a second small job — while thinset at 45 sq ft per bag needs 3 bags, since thinset coverage tracks raw floor area and doesn't shrink just because the grout total is small.
The two materials are sized by genuinely different logic here: grout scales with the length of every joint in the field, thinset scales with the area of the floor itself. A floor this size will always need multiple thinset bags even when the grout order rounds down to a single, mostly-unused one.
The same floor in 18 inch large-format tile, wider notch
| Room length | 9 ft |
|---|---|
| Room width | 11 ft |
| Tile length | 18 in |
| Tile width | 18 in |
| Joint width | 0.1875 in |
| Joint depth | 0.3125 in |
| Thinset coverage | 30 sq ft |
| Grout bag size | 20 |
| Grout bags | 1 20lb bags |
|---|---|
| Thinset bags | 4 50lb bags |
| Grout needed | 5.4 lbs |
| Tiled area | 99 sq ft |
Moving from 13 inch to 18 inch tile at the same joint width actually needs LESS grout, not more: 5.4 lbs instead of 7.4, because a bigger tile means fewer total tiles and therefore fewer linear inches of joint across the same floor, even though each individual joint is exactly the same size.
Thinset moves the opposite way — large-format tile needs a bigger trowel notch to keep full contact under a heavier, less flexible piece, and entering that lower 30 sq ft/bag coverage instead of 45 pushes the order from 3 bags to 4 on an identical floor area. Grout gets cheaper, thinset gets more expensive, and neither change is obvious from the tile size alone without running both numbers.
Common mistakes
- Applying the tile calculator's waste percentage to grout and thinset — these aren't wasted the same way tile is; buy by the volume/coverage formula instead, with a modest safety margin (~10%).
- Using a small trowel notch on large-format tile, which under-supports the tile and can cause hollow spots (lippage, cracking) — this doesn't just under-order thinset, it's a real installation failure mode.
- Guessing joint width instead of measuring — narrow joints (1/16 inch, common with rectified porcelain) use dramatically less grout than a 1/4-inch traditional joint.
- Mixing more thinset than can be applied and tiled within its open time (often 20-30 minutes depending on temperature and humidity), which causes it to skin over and lose adhesion before tile is even set into it.
- Not sealing natural stone grout joints (and sometimes the stone itself) after grouting, which is a separate step from the grout quantity calculation but affects long-term staining and durability.
Shopping summary
Buy thinset by the bag, rounded up from the manufacturer's coverage-per-bag figure for your trowel notch size; buy grout by the pound (or box), rounded up from the joint-volume formula plus about 10% for mixing loss and touch-ups.
Worked example: a 100 sq ft floor with a 1/4-inch square-notch trowel, at a manufacturer-stated coverage of roughly 60-70 sq ft per 50lb thinset bag for that notch size, needs about 2 bags. Grout for the same floor with 12x12 tile and 1/8-inch joints, at a typical published rate, commonly runs 2-3 lbs of grout per 10 sq ft — call it 20-30 lbs total, or one standard 25lb box plus a partial second.
FAQ
Can I use the same trowel notch for any tile size?
No — small mosaic tile typically needs a small notch (1/8-3/16 inch) while large-format tile needs a large notch (1/2 inch or bigger, sometimes with back-buttering added) to fully support the tile and avoid hollow spots.
Do wider grout joints need a different grout type?
Yes — joints 1/8 inch and under generally use unsanded grout, while wider joints use sanded grout, which resists shrinking and cracking at larger volumes.
How long does thinset need to cure before grouting?
Commonly 24-48 hours depending on the product, temperature, and humidity — grouting too early can disturb tiles that haven't fully bonded, so checking your specific thinset's cure window rather than assuming a flat 24 hours is worth the few extra minutes.
Is epoxy grout worth the extra cost over standard cement-based grout?
Epoxy grout resists staining and cracking better and doesn't need sealing, which makes it popular for kitchens and heavy-use floors, but it's more expensive, has a shorter working time, and is noticeably harder to apply cleanly — a real tradeoff worth weighing against a standard sanded or unsanded cement grout for the specific room.
Do I need a different thinset for large-format porcelain versus natural stone?
Yes — natural stone often needs a non-modified or stone-specific thinset to avoid staining or moisture issues some modified thinsets can cause with porous stone, while large-format porcelain typically calls for a polymer-modified, medium-bed thinset rated for its size and weight, so checking the tile manufacturer's specific thinset recommendation matters as much as the trowel-notch coverage figure.
Where to go next
The projects this number is a step of, the guides that explain the method behind it, and the rest of its trade group.