Grout Calculator

The formula

Coverage and yield assumptions

The density figure, about 0.0686 lb per cubic inch (1.9 g/cm³), is typical for cured cement grout. Manufacturer coverage charts from companies such as Custom Building Products give slightly different results by product, and epoxy grouts are often sold by volume in kits. Use your product's chart to check the final figure.

Sanded, unsanded or epoxy?

Unsanded grout is for joints narrower than 1/8 in and for polished stone or glass that sand could scratch. Sanded grout resists shrinkage in joints 1/8 in and wider. High-performance cement grouts and urethane or epoxy grouts are stain resistant and need no sealer; epoxy is also the choice for showers and kitchen counters that see heavy use, though it works fast and is harder to clean up.

Why small tiles take more grout

A square foot of 2 × 2 in mosaic has six times as much joint length as a square foot of 12 × 12 in tile. That is why mosaics, penny rounds and subway tile can consume a full bag in a small bathroom while a large-format floor barely uses one. The calculator reflects this through the (L + W) ÷ (L × W) term.

Mixing and applying

• Wait for the thinset to cure per the label, usually 24 hours, before grouting.
• Mix only what you can use in about 30 minutes.
• Pack joints diagonally with a rubber float and clean with a damp sponge.
• Seal cement grout once cured if the maker recommends it.

Color and consistency

Grout color can look different from batch to batch and dries lighter than it looks wet. Buy all bags for one room at once and mix full bags when possible so the shade stays even. Contrasting grout highlights tile shape; matching grout hides joint variation.

Common mistakes to avoid

• Using unsanded grout in joints wider than 1/8 in, which cracks and shrinks.
• Grouting before the thinset has cured.
• Mixing too much at once so it stiffens in the bucket.
• Using too much water while sponging, which weakens and lightens the joints.
• Filling change-of-plane corners with grout instead of flexible sealant.

Waste factor

10% accounts for grout left in the bucket, sponged off the surface and mixed but unused. Use 15–20% for first-time projects, textured tiles that trap grout on the face, or very small batches.

Imperial and metric

Switch the toggle above the inputs to enter in ↔ cm, sq ft ↔ m². The page converts metric entries to imperial before calculating, using NIST factors (1 ft = 0.3048 m, 1 in = 2.54 cm), and shows key results in both systems.

Worked examples

Floor, 12 × 12 tile

Inputs: tiled area 100 sq ft; tile length 12 in; tile width 12 in; tile thickness 0.375 in; joint width 0.125 in; waste factor 10%.

Result: You need about 8.5 lb of grout (3.9 kg).

• Units to buy (rounded up): 1 25 lb bags
• Joint volume: 113 cu in
• 25 lb bags: 1
• 10 lb bags: 1

Shower walls, 3 × 6 subway

Inputs: tiled area 80 sq ft; tile length 6 in; tile width 3 in; tile thickness 0.3125 in; joint width 0.0625 in; waste factor 15%; cost per unit $24.

Result: You need about 8.9 lb of grout (4 kg).

• Units to buy (rounded up): 1 25 lb bags
• Joint volume: 113 cu in
• 25 lb bags: 1
• 10 lb bags: 1
• Estimated material cost: $24.00

Mosaic floor, 2 × 2

Inputs: tiled area 40 sq ft; tile length 2 in; tile width 2 in; tile thickness 0.25 in; joint width 0.125 in; waste factor 15%.

Result: You need about 14.2 lb of grout (6.4 kg).

• Units to buy (rounded up): 1 25 lb bags
• Joint volume: 180 cu in
• 25 lb bags: 1
• 10 lb bags: 2

Quick reference for common sizes

The table repeats the first worked example at smaller and larger sizes, keeping every other setting the same, so you can see how the grout calculator result scales.

Limitations

Results assume square-edged tiles with full-depth joints. Tiles with pillowed or beveled edges take less grout; uneven handmade tiles may take more. Movement joints at walls and changes of plane are filled with sealant, not grout.