How this grout calculator works
Grout fills the joints between tiles, so the amount is the joint volume — width × depth — spread over the area, sized by the tile face:
weight = area × joint-per-ft² × (1 + waste) ÷ 1728 × 150 lb/ft³
At the defaults — 100 ft² of 12 × 12 in tile, 1/8 in joints, 3/8 in thick, 10% waste — that is 1.125 in³ of joint per ft², about 10.7 lb of grout, or one 25 lb bag at roughly $18; the full chain is in the worked example. The 150 lb/ft³ factor is set so coverage matches typical bag charts (about 256 ft² per bag here) — confirm on your product.
What sets how much grout you need
Four numbers drive grout, and tile size is the loudest of them:
- Tile size: smaller tiles mean more joints per square foot — a 6 in tile uses about twice the grout of a 12 in one.
- Joint width: a 3/16 in joint holds half again the grout of a 1/8 in joint — wider joints, more grout.
- Tile thickness: the joint is as deep as the tile is thick, so thick pavers take more than thin wall tile.
- Area: the tiled square footage — figure it on the tile calculator.
- Waste: 10% covers the grout left in the bucket and the bag you open for the last few feet.
Thinset, grout, and the two orders
A tile job needs two different materials, figured two different ways — don’t confuse them:
- Thinset (mortar): bonds the tile down, sized by trowel notch — about 95 ft² per 50 lb bag at 1/4 in square-notch, 70 at 1/4 × 3/8, 45 at 1/2 in.
- Grout: fills the joints after the thinset cures, sized by joints — this calculator.
- Trowel size: bigger tile needs a bigger notch and more thinset per foot — that is the thinset table below.
- Sealer: cementitious grout wants a penetrating sealer; epoxy grout does not.
- Spacers & sponges: small consumables — grab them with the grout.
Grout by tile size, and thinset by trowel
Table 1 shows how tile size drives grout, per 100 ft² at a 1/8 in joint; Table 2 is thinset coverage by trowel notch.
| Tile | Grout |
|---|---|
| 24 × 24 in | 4.9 lb |
| 12 × 12 in | 9.8 lb |
| 6 × 6 in | 19.5 lb |
| 3 × 6 subway | 29.3 lb |
| 2 × 2 mosaic | 58.6 lb |
| Trowel notch | Coverage |
|---|---|
| 3/16 in V | ≈ 100 ft² |
| 1/4 × 1/4 in | ≈ 95 ft² |
| 1/4 × 3/8 in | ≈ 70 ft² |
| 1/2 × 1/2 in | ≈ 45 ft² |
How to figure grout for a job
- Measure the tiled area in square feet — total odd rooms on the square footage calculator.
- Enter the tile size — length and width in inches. This is the biggest lever.
- Set the joint width and tile thickness — the joint is as deep as the tile.
- Add 10% waste for the grout left in the bucket and the partial last bag.
- Read the pounds and bags, and grab thinset separately from the trowel table.
Worked example: 100 ft² of 12 × 12 tile
The default, worked line by line — 100 ft², 12 × 12 in tile, 1/8 in joints, 3/8 in thick, 10% waste, 25 lb bags:
total = 100 × 1.125 × 1.10 = 123.75 in³
weight = 123.75 ÷ 1728 × 150 = 10.74 lb
bags = ⌈10.74 ÷ 25⌉ = 1 bag · cost = $18
One bag covers this whole floor with two-thirds of it to spare, which is why the pounds matter more than the bag count here — buy the one bag and keep the rest for repairs. Swap the tile to 3 × 6 subway and the same 100 ft² jumps past 30 lb and two bags, because there are three times the joints to fill.
What this grout estimate doesn’t include
It sizes the grout; a tile job carries more:
- Thinset. The setting mortar under the tile — a separate order by trowel size.
- Sealer. A penetrating sealer for cementitious grout, reapplied over time.
- Tile and trim. The tile itself, bullnose and edge pieces — on the tile calculator.
- Backer board and membrane. Cement board or an uncoupling membrane under the thinset.
- Consumables. Spacers, sponges, mixing paddle and buckets.
Grout FAQ
How much grout do I need?
Grout fills the joints, so it depends on the tiled area, the tile size, the joint width and the tile thickness. For 100 ft² of 12 × 12 in tile with 1/8 in joints, 3/8 in thick, that is about 10.7 lb — one 25 lb bag with plenty to spare. Smaller tiles have more joints and use far more grout for the same floor.
How do I calculate grout for tile?
The joint volume per square foot is the joint width × the tile thickness × (tile length + width) ÷ (length × width), times 144. Multiply by the area and a coverage factor for the weight. The key driver is tile size: the smaller the tile, the more linear feet of joint per square foot, and the more grout.
How much grout for 100 square feet?
It depends entirely on the tile. In 12 × 12 in tile with 1/8 in joints that is about 10.7 lb (one 25 lb bag); in 3 × 6 in subway tile it is roughly 29 lb before waste — nearly three times as much — because there are three times the joints. Enter your tile size and the calculator sizes it.
How much thinset do I need for tile?
Thinset (the mortar that bonds tile to the substrate) is sold separately and figured by trowel size, not joints. A 50 lb bag covers roughly 95 ft² with a 1/4 × 1/4 in square-notch trowel, about 70 ft² with a 1/4 × 3/8 in, and near 45 ft² with a 1/2 × 1/2 in for big tile. The tile calculator estimates thinset bags.
Does tile size change how much grout I need?
Hugely. At the same joint and thickness, 6 × 6 in tile uses about twice the grout of 12 × 12, and 2 × 2 in mosaic several times more — the reference table shows the spread. Big-format 24 × 24 tile uses the least. Always size grout to your actual tile, not a rule of thumb.
What is the difference between sanded and unsanded grout?
Sanded grout has fine sand for strength and is used for joints 1/8 in and wider — most floors and walls. Unsanded grout is smoother, for joints 1/16 in and narrower and for polished stone that sand would scratch. This calculator estimates by volume, which applies to either; check the specific bag for its coverage.
How much does tile grout cost?
Sanded grout runs about $15–25 for a 25 lb bag, and a bag covers a lot of large tile, so grout is rarely a big line on a job. Epoxy grout costs several times more but resists stains and never needs sealing — worth it in showers and on kitchen counters.
Sources and standards
The volume is geometry; the coverage is calibrated to product charts:
- Joint volume: joint width × depth × (L + W) ÷ (L × W) — the tiled-area joint geometry.
- Coverage factor: ~150 lb per ft³ of joint, set to match typical sanded-grout bag charts.
- Sanded vs unsanded: sanded for joints ≥ 1/8 in, unsanded for ≤ 1/16 in and polished stone.
- The bag governs: coverage varies by product — confirm the number printed on your grout.
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