Grout Calculator
Pounds or kilograms and bags of grout from tile size, thickness and joint width, including 12×24 tile over 100 sq ft.
Your estimate
6.2 lb
Grout needed (incl. 10% waste)
- Bags
- 1 × 25 lb
- Coverage per 25 lb bag
- 353 sq ft
- Tiled area
- 80 sq ft
- Joint volume
- 89 cu in (1.45 L)
Show the math
- Area = L × W = 80 sq ft; tile 12 × 12 × 3/8 in, joint 1/8 in
- Grout volume per area = joint × depth × (tile L + tile W + joint) ÷ ((tile L + joint) × (tile W + joint))
- = 1.11 cu in per sq ft → 89 cu in
- × 1.77 kg/L (≈ 110.5 lb per cu ft) = 5.7 lb; + 10% = 6.2 lb
- ÷ 25 lb per bag → 1 bag
Shopping list & cost
| Item | Spec | Qty | Cost |
|---|---|---|---|
| Sanded grout | 25 lb bags, 1/8 in joints | 1 bag | — |
| Grout float, sponge, bucket | hard rubber float | 1 set | — |
| Grout sealer (cement grout) | after full cure | per label coverage | — |
Prices are what you enter under Advanced options. Estimates only — check stock and pricing with your supplier.
Quick answer Grouting 80 sq ft of 12 × 12 in floor tile (⅜ in thick) with ⅛ in joints takes about 6.2 lb of sanded grout including 10% waste — 1 × 25 lb bag, which covers about 353 sq ft at this tile size. A 7.5 m² floor of 300 × 300 mm tile with 3 mm joints needs 2.9 kg. Smaller tiles and wider joints use far more grout: 2 × 2 in mosaic needs nearly four times as much per square foot.
Method & assumptions
Grout volume per area = J × T × (L + W + J) ÷ ((L + J) × (W + J)) Grout weight = Area × volume per area × 1.77 kg/L (0.064 lb per cu in) Bags = Weight × (1 + waste %) ÷ bag weight, rounded up
- L, W
- tile length and width
- T
- tile thickness = joint depth
- J
- joint width
- 1.77 kg/L
- cured cement grout, calibrated to the CUSTOM Polyblend coverage chart
Assumptions & limits
- Joints are filled to the full thickness of the tile; joints left shallow by squeezed-up thinset use less.
- Density of cement-based sanded or unsanded grout ≈ 1.77 kg/L; our coverage matches the manufacturer's published chart within about 2% across tile sizes.
- Premixed urethane and epoxy grouts are sold by volume in kits — use the volume figure and check the kit's coverage.
- Waste covers mixing leftovers, sponge-off and deeper joints at cut edges.
Rounding: purchase quantities are always rounded up to whole units as sold. See our methodology.
Diagram
How to use this calculator
- Measure the tiled area — length × width of the floor or wall section.
- Enter the tile length, width and thickness. Thickness matters because grout fills the joint to the full depth of the tile.
- Enter the joint width you will set with spacers: 1/16 in for wall tile and rectified tile, ⅛–3/16 in for most floors, ¼ in or more for rustic tile.
- Choose sanded grout for joints ⅛ in (3 mm) and wider, unsanded for narrower joints.
- Pick the bag size you can buy and keep 10% extra for mixing and clean-up.
Worked examples
Imperial: 5 × 8 ft bathroom, 12 × 24 in porcelain, ⅜ in thick, ⅛ in joints
- Volume = 0.125 × 0.375 × 36.125 ÷ (12.125 × 24.125) × 144 = 0.834 cu in per sq ft
- 40 sq ft × 0.834 = 33 cu in ≈ 2.1 lb; +10% = 2.3 lb
- A 10 lb bag is plenty — a 25 lb bag would cover about 469 sq ft
Metric: 3 × 2 m shower wall, 200 × 100 × 8 mm tile, 2 mm unsanded joints
- Volume = 2 × 8 × 302 ÷ (202 × 102) mm = 0.235 L per m²
- 6 m² × 0.235 = 1.41 L × 1.77 = 2.5 kg; +10% = 2.7 kg
- One 5 kg bag
Imperial: 100 sq ft of 12 × 24 in tile, ⅜ in thick, ⅛ in joint
- The table on this page lists 469 sq ft per 25 lb bag for this size (CUSTOM’s chart says 461).
- 100 sq ft is 5.3 lb before extra. With the default 10%: 5.9 lb.
- Buy 1 × 25 lb bag. A 12×12 in tile at the same thickness and joint uses more grout; do not reuse that pound figure here.
In depth: grout planning notes
Why tile size matters more than area
Grout fills the joints, not the floor, so what drives the quantity is the total length of joint and its cross-section. Small tiles have far more joint per square foot: a square foot of 12 × 12 in tile has about 2 ft of joint, a square foot of 2 × 2 in mosaic has about 12 ft. That is why the same 25 lb bag covers roughly 350 sq ft of 12 in tile but under 100 sq ft of 2 in mosaic at the same ⅛ in joint. Width and depth scale the answer directly: going from ⅛ to ¼ in joints roughly doubles the grout, and ½ in thick tile needs a third more than ⅜ in tile.
The formula on this page computes the joint volume around each tile footprint and converts it to weight with a cured density of about 1.77 kg per liter. We calibrated that density against CUSTOM's published Polyblend chart; across tile sizes from 1 in mosaics to 24 in porcelain our coverage lands within about 2% of the chart. Premixed urethane and epoxy grouts are sold by volume rather than weight, so for those use the joint volume the calculator shows and compare it with the kit's stated yield.
Choosing and working the grout
Sanded grout contains fine sand that resists shrinkage in wider joints and is the normal choice for floor joints of ⅛ in and up. Unsanded grout is smoother and sticks to vertical surfaces better, which suits wall tile with 1/16 in joints, but it can shrink and crack in wide joints. Polished marble, glass and some glazed tiles scratch easily, so unsanded or a non-abrasive premixed grout is safer even where the joint is near ⅛ in. Epoxy grouts resist stains and need no sealer, but they set faster and are harder to clean up — practice on a small area first.
Wait for the thinset to cure (often 24 hours), then work in small sections: pack the joints diagonally with a hard rubber float, strike off the excess, and sponge with a barely damp sponge once the grout firms up. Over-wet sponging pulls cement out of the joint and leaves it weak and blotchy. Cement-based grout is usually sealed after it has cured for two to three days; check the bag. Keep one bag back from the same lot for future repairs, because color varies from batch to batch.
Reference table
| Tile (L × W × T), joint | Sq ft per 25 lb bag |
|---|---|
| 1 × 1 × ¼ in mosaic, ⅛ in | 52 (chart 54) |
| 2 × 2 × ¼ in mosaic, ⅛ in | 95 (chart 96) |
| 6 × 6 × ¼ in, ⅛ in | 269 (chart 266) |
| 12 × 12 × ⅜ in, ⅛ in | 353 (chart 348) |
| 12 × 12 × ⅜ in, ¼ in | 179 (chart 177) |
| 12 × 24 × ⅜ in, ⅛ in | 469 (chart 461) |
| 24 × 24 × ⅜ in, ⅛ in | 700 (chart 688) |
Key facts
- Sanded grout
- joints ⅛ in (3 mm) and wider
- Unsanded grout
- joints under ⅛ in; polished stone and glass
- Doubling the joint width
- roughly doubles the grout
- Cure before sealing
- typically 48–72 hours (check the bag)
Tips & common mistakes
- Mix only what you can work in about 20–30 minutes; grout that has started to stiffen should not be re-tempered with more water.
- Buy all bags from the same lot number — color can vary between batches.
- Rake out squeezed-up thinset from the joints before it sets so the grout has its full depth.
- Use caulk, not grout, at changes of plane (inside corners, tub and countertop joints) where movement happens.
Frequently asked questions
How much grout for 12×24 tile?
For 100 sq ft of 12×24 in tile, 3/8 in thick, with a 1/8 in joint and the default 10% extra, the estimate is 5.9 lb. Buy 1 × 25 lb bag. The coverage table on this page lists 469 sq ft per 25 lb bag for that size (CUSTOM’s chart says 461). A 12×12 in tile at the same thickness and joint uses more grout because the joint length is longer. Sanded grout is the usual choice at 1/8 in. Count the tiles on the tile calculator and the thinset on the thinset calculator.
How much grout do I need for 100 square feet?
For 12 × 12 in tile ⅜ in thick with ⅛ in joints, about 7 lb (8 lb with waste) — a third of a 25 lb bag. For 6 × 6 in tile it is about 9.3 lb; for 2 × 2 in mosaic about 26 lb.
How many square feet does a 25 lb bag of grout cover?
It depends on tile size and joint width: about 350 sq ft for 12 × 12 in tile with ⅛ in joints, 180 sq ft with ¼ in joints, and under 100 sq ft for 2 × 2 in mosaics.
Should I use sanded or unsanded grout?
Sanded for joints ⅛ in (3 mm) and wider — the sand stops shrinkage cracks. Unsanded for narrower joints and for surfaces sand could scratch, like polished marble or glass.
Does tile thickness change how much grout I need?
Yes, in direct proportion. A ½ in thick tile needs a third more grout than ⅜ in tile with the same joint, because the joint is deeper.
How much grout do I need for a backsplash?
Very little: a 20 sq ft subway-tile backsplash with 1/16 in joints takes about 2 lb, so a 7–10 lb bag or box of unsanded grout is enough.
How do I calculate grout for regrouting?
Use the depth you rake out (usually ⅛ in, not the full tile thickness) as the thickness. Regrouting 1/8 in deep uses about a third of the grout of a new ⅜ in tile installation.
Sources
- CUSTOM Building Products – Polyblend Sanded Grout technical data sheet TDS-129 (PDF) — accessed : “Coverage for 25 lb bag: 12" x 12" x 3/8" tile, 1/8" joint – 348 ft² (32.3 m²); 3/16" – 234 ft²; 1/4" – 177 ft²”
- Tile Council of North America – TCNA Handbook — general reference — not cited for a specific figure
- ANSI A108.10 – installation of grout in tilework — general reference — not cited for a specific figure
Default values (yields, coverage rates and densities) are typical figures from manufacturer literature. Always check the label on the product you buy.
Related calculators
- Tile CalculatorCount floor or wall tiles and boxes, including a 100 sq ft bathroom, with joints and overage for straight, offset, diagonal or herringbone.
- Thinset CalculatorBags of thinset by trowel notch, bag weight and back-buttering, including 12×24 tile over 100 sq ft.
- Backsplash CalculatorKitchen backsplash tile estimate: subway tiles or mosaic sheets for the counter run and the taller section behind the range, plus grout, adhesive and trim.
Learn more in our guides
Method, waste and worked examples: Tile quantities: layout waste, grout and thinset.
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DIYCalcLab. “Grout Calculator.” Nov 6, 2026. https://diycalclab.com/tile/grout-calculator/
Estimates only. Verify quantities with your supplier and local building codes. For structural, electrical or safety-critical work, consult a licensed professional. Full disclaimer.