Tile Grout Calculator

Grout is easy to under-buy, because the amount doesn’t scale with floor area alone. Small tiles have far more joint length per square foot than large ones; wider and deeper joints hold more; and every job loses some to mixing and spillage. This calculator combines all of that into a volume estimate you can take to the grout aisle.

The grout volume formula

is the tiled area in square feet (×144 to reach square inches), and are the tile length and width in inches, and are the grout joint width and depth in inches, and is the waste percentage. The bracketed term is the fraction of the surface that’s joint — it grows as tiles shrink or joints widen.

Worked example

The calculator’s defaults are 100 sq ft of 12 × 12 inch tile, 1/8-inch (0.125) joints, 3/8-inch (0.375) deep, 10% waste.

Joint fraction:

Volume:

That’s cubic feet.

Tile Grout Calculator worked example diagram — A visual read of the worked example above — the same numbers the calculator returns for its default inputs.

How tile size drives grout use

Same 100 sq ft, 1/8-inch joints 3/8-inch deep, 10% waste:

Tile size	Grout volume
2 × 2 in (mosaic)	~742 cu in
4 × 4 in	~371 cu in
6 × 6 in	~247 cu in
12 × 12 in	~124 cu in
24 × 24 in	~62 cu in

A mosaic sheet uses roughly six times the grout of large-format tile over the same floor.

How to Calculate Tile Grout (step by step)

Step One: Convert the tiled area to square inches

The calculator uses inches for tile and joint dimensions, so convert the coverage area from square feet to square inches.

Tiled area = 100 × 144 = 14,400 sq in

Step Two: Calculate the grout joint volume for one tile pattern

For a repeating tile pattern, estimate the joint length around one tile, then multiply it by the joint width and depth.

Joint length = 2 × (tile length + tile width)
Effective shared joint length per tile = 12 + 12 = 24 in

Joint volume ratio = (0.125 × 0.375 × 24) ÷ (12 × 12)
Joint volume ratio = 0.0078125

Step Three: Calculate the base grout volume

Multiply the converted area by the joint volume ratio.

Base grout volume = 14,400 × 0.0078125 = 112.50 cu in

Step Four: Add the waste allowance

The default waste allowance is 10%, so multiply the base volume by 1.10.

Grout needed = 112.50 × (1 + 10 ÷ 100)
Grout needed = 112.50 × 1.10 = 123.75 cu in

Step Five: Convert the result to cubic feet

There are 1,728 cubic inches in one cubic foot.

Grout needed = 123.75 ÷ 1,728 = 0.072 cu ft

What your results mean

The primary result is the estimated grout volume in cubic inches. The cubic-foot result gives the same estimate in a larger unit that can be easier to compare with product packaging or bulk material measurements.

This is a volume estimate, not a bag count. Grout products differ in powder density, mixing ratios, and coverage efficiency, so use the product label to convert the calculated volume into the number of bags or containers to purchase. Buying slightly more than the exact estimate is usually safer than running short during installation.

For irregular tiles, wide joints, highly textured tile faces, or uneven substrates, increase the waste allowance. A careful installation with consistent joint depth will generally use less grout than a rough or irregular surface.

About the formula: The estimate treats grout joints as a continuous grid around each tile, then adds the selected waste allowance. Area is converted from square feet to square inches before calculating the joint volume.

Frequently Asked Questions

How much grout for 100 square feet of 12-inch tile with 1/8-inch joints?+

About 124 cubic inches including 10% waste, roughly 0.07 cubic feet. Check that figure against your grout bag's stated coverage to get a bag count.

Does this include a waste allowance?+

Yes, 10% by default (the volume is multiplied by 1.10). Raise it for uneven substrates, porous or textured tile, or if you're new to grouting.

Why do smaller tiles need more grout?+

More joint length per square foot. A 4-inch tile has three times the joint length of a 12-inch tile over the same area, so it uses about three times the grout. The formula captures this through tile perimeter over tile area.

Should grout depth equal the tile thickness?+

No — use the depth of the joint that actually gets filled, which is usually less than the tile is thick once you account for the adhesive bed. Measure it after the tiles are set.

How do I turn cubic inches of grout into bags?+

Grout coverage charts are given per bag for a specific tile size and joint width. Match your tile and joint to the chart, or divide your volume by the bag's yield (many 25-lb bags of sanded grout yield roughly 300–400 cubic inches mixed).

Sanded or unsanded grout?+

Sanded for joints 1/8 inch and wider; unsanded for joints narrower than 1/8 inch and for polished or scratch-prone tile like marble and glass. Coverage differs, so use the matching product's chart.