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Grout Calculator

Grout usage swings wildly with tile size and joint width. A bag can cover 768 sq ft or 7. This calculator works straight from MAPEI's published coverage chart, so the answer matches the bag you'll actually buy.

Diagram of tiles with grout joints, showing how tile plus joint sets the true coverage per tile
Tiles plus the grout joint between them set the true coverage per tile.

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Enter your measurements

How the grout quantity is calculated

There is no honest one-line formula for grout. Coverage depends on tile size, tile thickness and joint width together. So this calculator uses the manufacturer's own chart: MAPEI's Keracolor S technical data sheet lists the square feet a 25 lb bag covers for each tile size and joint width. For example, 12 × 12 in tiles with a 1/4 in joint: 191 sq ft per bag; the same tiles at 1/8 in: 383 sq ft.

Pounds needed = your area (plus waste allowance) ÷ chart coverage × 25, rounded up to whole bags. Keracolor S comes in 25 lb and 10 lb bags; the calculator scales the chart's per-pound coverage to whichever size you pick. Another brand's own chart is the last word for its product. Only tile sizes that appear in MAPEI's published chart are offered, and the figures are for sanded cement grout. Epoxy and unsanded grouts cover differently, so check their data sheets. The chart's figures also assume the standard tile thickness in MAPEI's table for each size (12 × 12 at 3/8 in thick, 4 × 8 at 1/2 in, 6 × 6 at 1/4 in): a tile thinner than the chart assumes will use slightly less grout than shown.

Still counting tiles? Start with the Tile Calculator, which uses the same measurements.

Sources

The figures behind this calculator come from published manufacturer data and industry standards:

Worked examples

200 sq ft floor, 12 × 12 in tiles

1/4 in joints, 10% waste. MAPEI chart coverage: 191 sq ft per 25 lb bag.

Buy 2 × 25 lb bags

60 sq ft shower walls, 6 × 6 in tiles

1/8 in joints, 10% waste. Chart coverage: 285 sq ft per bag.

Buy 1 × 25 lb bag

1,000 sq ft, 24 × 24 in tiles

3/16 in joints, 10% waste. Chart coverage: 510 sq ft per bag.

Buy 3 × 25 lb bags

Frequently asked questions

How much grout do I need for 100 sq ft of 12×12 tile?
With 1/8 in joints, MAPEI rates a 25 lb bag at 383 sq ft, so one bag is plenty. Widen the joint to 1/4 in and coverage drops to 191 sq ft; you'd need about 13 lb, still one bag, but with far less spare.
Why does joint width change grout use so much?
Grout fills the joint volume: double the width and you roughly double the grout. Small tiles multiply the effect because there are far more joints per square foot: 1×1 mosaics at wide joints can need 12× more grout than large tiles.
Sanded or unsanded grout: does coverage differ?
Yes. This calculator uses MAPEI's sanded grout (Keracolor S) chart, for joints 1/8 in and wider. For joints under 1/8 in or delicate glazed and polished tiles, use unsanded grout and its own coverage chart.
How much extra grout should I allow?
10% covers spillage, the grout that washes out during cleanup, and joints that run slightly deeper than the tile. Keep any leftover dry grout for future repairs. Colours vary between batches.
One bag is open. Can I store the rest?
Yes, dry grout powder keeps for months in a sealed container in a dry place (MAPEI rates the shelf life at 2 years unopened). Never mix a full bag if you only need part of it.

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Estimate disclaimer: results are planning estimates based on standard manufacturer yields and coverage figures. Site conditions, product choice and installation method change actual quantities. Verify before you buy, and follow local building code for structural work. This tool does not replace professional engineering advice.

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