Grout Calculator

How it works

joint share = joint × (L + W) ÷ ((L + joint) × (W + joint)) · hexagon: 2 × size × joint ÷ (size + joint)² · grout per area = joint share × tile thickness × grout density · total = per area × area × (1 + waste%) · bags = ⌈total ÷ bag size⌉

Grout fills the lines between tiles, so the amount depends on what share of the surface is joint and how deep the joint is. Each tile plus its joint repeats across the floor, and the joint lines along a tile’s edges divided by that repeat area give the share of the surface taken by grout — larger for small tiles and wide joints, smaller for large-format tile. Multiplying by the tile thickness gives the joint volume per square foot or square meter, and multiplying by the grout density gives the weight of powder to buy. The densities used — about 1.8 g/cm³ for sanded and 1.72 for unsanded cement grout — are worked back from manufacturer coverage charts, so the result lands within a few percent of the charts printed on the bag; epoxy kits are lighter per volume. The waste allowance covers what is left in the bucket and washed off. The coverage chart shows how the amount and the square footage per bag change if you choose a different joint width, and hexagon tiles use their own geometry.

Worked example

For 100 ft² of 12 × 12 in tile, 3/8 in thick, with 1/8 in joints and sanded grout: the joint share is 0.125 × 24 ÷ (12.125 × 12.125) = 2.04%. Over a square foot that is 2.04% × 144 in² × 0.375 in = 1.10 in³ of joint, and at 1.8 g/cm³ (0.065 lb/in³) it takes 0.072 lb/ft². So 100 ft² needs 7.2 lb, or 7.9 lb with 10% waste — one 25 lb bag, which covers about 349 ft² of this tile, in line with the 348 ft² printed on a common sanded grout chart.

Sources: Custom Building Products — Polyblend Sanded Grout data sheet (TDS-129) coverage chart · Custom Building Products — Polyblend Non-Sanded Grout data sheet (TDS-130) · Custom Building Products — CEG-Lite epoxy grout data sheet (TDS-101)

Frequently asked questions