Tile Calculator — Tile, Thinset & Grout Estimator
A 120 ft² floor in 12" tile with 1/8" joints needs 132 tiles, 2 bags of thin-set at a 1/4" notch, and 1 bag of grout. The joints occupy 2.05% of the floor — this calculator derives grout from that geometry instead of a manufacturer's chart, so it stays right for any tile size. Coverage figures verified 2026-08-04.
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Prepared with MaterialMath — https://estimatormath.com. Quantities are estimates based on the dimensions entered and the published figures cited on the tool page (verified 2026-08-04). Verify against your own measurements and your supplier's actual pack sizes before ordering. Not professional engineering, construction or financial advice.
How is tile, thin-set and grout calculated?
Tile quantity is an area calculation with one refinement most calculators miss. Thin-set comes from a published coverage chart. Grout is the interesting one, and this calculator derives it from geometry rather than looking it up — which is why it produces a sensible answer for tile sizes and joint widths no chart covers.
The cell-area idea is worth dwelling on because it goes the opposite way from what people expect. A 12" tile with 1/8" joints does not cover one square foot of floor — it covers a cell of 12.125" × 12.125", which is 147.016 in², or 1.0208 ft². So a 120 ft² floor takes 132 tiles before waste, not 120. The effect grows as tiles get smaller: on a 3" mosaic with 1/16" joints the joints are over 4% of the floor.
Where the grout number comes from
Take one repeating cell. Its area is (L + J) × (W + J). The tile inside it has area L × W. The difference is grout footprint, and dividing by the cell area gives the fraction of the floor that is joint. Multiply that fraction by the joint depth — the tile thickness, which is what a properly packed joint fills — and you have volume of grout per unit of floor. No chart, no lookup, no interpolation.
| Tile | Joint | Grout share of floor | Litres per 100 ft² |
|---|---|---|---|
| 3" × 6" subway | 1/16" | 3.05% | 2.25 L |
| 6" × 6" | 1/8" | 4.04% | 2.98 L |
| 12" × 12" | 1/8" | 2.05% | 1.82 L |
| 12" × 24" | 3/16" | 2.30% | 2.04 L |
| 24" × 24" | 3/16" | 1.54% | 1.44 L |
Computed at build time by the same function the calculator uses. Note that subway tile takes over three times the grout of a 24" tile for the same floor area — small tile is mostly joint.
A worked example: a 120 ft² bathroom floor
12" × 12" porcelain, 3/8" thick, 1/8" joints, 1/4" × 1/4" square notch, 12% tile waste and the default 50% grout allowance.
Step by step
- Repeating cell
- 12.125 × 12.125 = 147.02 in²
- Grout share of floor
- (147.02 − 144) ÷ 147.02 = 2.05%
- Tiles including 12% waste
- 132 tiles
- Thin-set at 95 ft²/bag
- 63 lb → 2 × 50 lb bags
- Grout in the joints
- 2.18 litres
- Grout to buy, +50%
- 11.9 lb → 1 × 25 lb bag
The grout line shows why the allowance is set high. The joints physically hold 2.18 litres — under a gallon. But you will mix more than that, leave some in the bucket, lose some into the bottoms of the joints where the tile is not perfectly bedded, and pull some back out in the first wash. Buying the second bag costs about twenty dollars. Discovering you are short two-thirds of the way across a floor, with a dye lot you may not be able to match, costs the floor.
Who this calculator is for
- DIY tilers doing a bathroom or kitchen who need all three materials in one place rather than three separate lookups.
- Tile setters pricing a job, particularly on unusual tile sizes where published coverage charts do not have a row.
- Anyone laying large-format tile — the tool flags the TCNA flatness requirement as soon as a tile side reaches 15", which is the point at which substrate preparation stops being optional.
- People comparing tile sizes. Switching from 12" to 24" tile roughly halves the grout and changes the trowel, and both show up immediately.
For plank flooring rather than tile, use the flooring calculator. If you are tiling over a new slab, check the concrete calculator and give the slab its full cure before tiling.
What this calculator does not account for
- Substrate flatness. The thin-set figure assumes a flat floor. A wavy one can take 30–50% more mortar, and with large-format tile it is not optional to fix — the tile will not bridge it.
- Waterproofing and crack isolation membranes. Required in showers and strongly advisable over any slab with movement. They are a separate material and a separate cost.
- Epoxy grout. Different yield, different working properties, sold by the unit rather than the pound. Nothing here applies to it.
- Layout and pattern. The waste slider is where layout lives. A diagonal or herringbone lay needs it raised, and the tool does not infer the pattern from anything you enter.
- Trim, bullnose and transitions. Edge pieces are counted by the lineal foot of exposed edge, not by area, and are not in this calculation.
- Movement joints. The TCNA requires them at the perimeter and at intervals across large fields. They are filled with sealant, not grout, and skipping them is a common cause of tenting.
Thin-set coverage by trowel notch
| Notch | Coverage per 50 lb bag | Suits |
|---|---|---|
| 3/16" V-notch | 140 ft² | Mosaic and tile under 6" |
| 1/4" × 1/4" square notch | 95 ft² | Tile 6"–12" |
| 1/4" × 3/8" square notch | 75 ft² | Tile 12"–16" |
| 1/2" × 1/2" square notch | 45 ft² | Large format 16"+ and natural stone |
| 3/4" × 5/8" euro notch | 30 ft² | Large format with back-buttering |
From Custom Building Products and MAPEI published technical data, cross-checked between the two. All figures assume a flat substrate and full trowel ridges collapsed by the tile — a partially bedded tile uses less mortar and fails sooner.
Common questions
How many 12x24 tiles do I need for 100 square feet?
Including a 12% waste allowance and the joint-cell geometry above, 100 ft² of 12×24 plank tile needs 56 tiles. Set your own area and joint width above for an exact count — plank tile's larger cell means fewer pieces than the same area in 12×12.
How many bags of thinset per 100 sq ft?
For 100 ft² of 12×24 tile with a 1/4"×3/8" notch (the usual choice for this size), budget 2 × 50 lb bags. A smaller notch on smaller tile uses less; a larger notch or a wavy floor uses more — the calculator above recomputes for your exact trowel and tile size.
What waste percentage should I add for a diagonal tile layout?
17% for a 45° diagonal lay, versus 12% for a straight lay — the diagonal cuts two triangular offcuts at every wall instead of one straight cut, and neither triangle is reusable elsewhere. Herringbone runs higher still, around 22%, because almost every piece at the perimeter needs its own cut.
How many tiles come in a box?
It depends entirely on the tile — a box is priced and packed by the manufacturer, not by a fixed count, and ranges from 3–4 large-format tiles to 20+ small mosaics per box. Enter your carton's printed coverage into the "box coverage" field above and the calculator converts your tile count into a box count automatically.
How much grout do I need for tile?
Grout volume is pure geometry: the joints occupy a known fraction of the floor, and that fraction times the joint depth is the volume. For 12" tile with 1/8" joints, the grout occupies 2.05% of the floor area. At 3/8" deep that works out to about 0.65 litres per 100 ft².
This calculator computes that directly rather than reading a manufacturer's chart, which means it stays right for tile sizes and joint widths no chart covers. It then adds a practical allowance — see the question below, because that allowance is large and it is not padding.
Why does the grout figure include 50% waste?
Because grout genuinely disappears at a rate tile does not. Material is lost filling irregularities in the bottom of the joint, left clinging to the bucket and the float, and pulled back out during the first cleanup pass before it sets.
The asymmetry is what drives the number. Surplus grout costs a few dollars. Running short of a dye-lot grout mid-floor means either a visible colour change across the room or chipping out and redoing what you have already grouted. Fifty percent is the default and it is adjustable, but do not take it below about 25%.
How many tiles do I need?
Fewer than the naive answer, and this calculator gives you the accurate one. A tile laid in a grid does not occupy its own area of floor — it occupies a repeating cell of (length + joint) × (width + joint), because each tile owns one joint on two of its four sides.
For a 12" tile with 1/8" joints the cell is 12.125" square, so each tile covers 1.0208 ft² rather than 1.00 ft². Counting on bare tile area over-orders by about 2% on a 12" tile and by nearly 8% on a 3" mosaic. On a large job that is real money.
How much thin-set mortar do I need?
Thin-set is quoted by trowel notch, not by tile size, because the notch determines the depth of the bed. A 1/4" × 1/4" square notch covers about 95 ft² per 50 lb bag; a 1/2" × 1/2" notch covers about 45.
The important caveat is that those figures assume a flat substrate. On a wavy floor the notch depth is only where you start — filling the hollows can push consumption 30–50% above the chart. If your floor is out of flat, check it before you buy, because large-format tile makes the problem worse rather than hiding it.
Should I use sanded or unsanded grout?
Sanded at 1/8" and wider, unsanded below. The rule is about shrinkage: unsanded grout shrinks as it cures and will crack in a wide joint, while sanded grout physically cannot pack into a joint narrower than about 1/8".
The other consideration is the tile itself — sanded grout will scratch polished stone, glass and some glazed tile. If you have narrow joints in a scratch-prone tile, unsanded is the only option and that is fine, because narrow joints are what it is for.
What counts as large-format tile and why does it matter?
Under the TCNA Handbook, any tile with one side 15 inches or longer is large format. The practical consequences are substantial: the substrate must be flat to within 1/8" in 10 ft, back-buttering becomes effectively mandatory, and you need a larger notch and often a medium-bed mortar.
A big tile cannot bend to follow a floor the way a 6" tile can, so every hollow under it becomes either a void — which cracks the tile later — or extra mortar. This is the single most common reason a large-format job consumes far more thin-set than the chart predicted.
Sources for the figures used
Every rate, coverage figure and code limit in this calculator comes from a published source. Where a figure is a convention rather than a standard, it says so.
- TCNA Handbook for Ceramic, Glass and Stone Tile Installation — Large-format definition, substrate flatness tolerance, and installation methods (checked 2026-08-04)
- Custom Building Products technical data sheets — Thin-set coverage per trowel notch (checked 2026-08-04)
- MAPEI technical data sheets — Cross-check on mortar coverage figures (checked 2026-08-04)
- Grout volume derivation — Computed from joint geometry in this calculator; the full derivation is published in the section above rather than taken from a chart (checked 2026-08-04)