How much grout do I need for 100 sq ft of 12×12 tile?

With 1/8 in joints, roughly 8.5 lb of sanded grout — one 25 lb bag leaves you comfortable spare, while a 10 lb bag leaves almost nothing for mistakes. Enter your exact tile and joint sizes above for your own figure.

Why does small tile use so much more grout?

Grout fills joints, and joints run along every tile edge. A floor of 2 in mosaics has about six times the joint length per square foot of a 12 in tile floor, so it uses several times the grout even at the same joint width.

Should I use sanded or unsanded grout?

Use sanded grout for joints 1/8 in and wider — the sand stops the grout shrinking and cracking in the joint. Use unsanded for narrower joints and for polished marble or glass, which sand can scratch. The calculator adjusts its density figure for the type you pick.

Does joint depth matter as much as joint width?

They multiply together, so yes — doubling either one doubles the grout volume. Joint depth is usually close to the tile thickness; if your tiles are thin (1/4 in), lower the depth figure and watch the estimate fall.

Can I mix grout from two different bags on one floor?

You can, but colour can vary slightly between batches and dye lots. The safer approach the calculator supports is buying enough of one bag size to finish the visible area from a single lot, keeping the second bag for repairs.

Grout Calculator — Free, With Formula & Worked Example

About this calculator

Grout consumption is driven by joint volume: bigger tiles with narrow joints use surprisingly little, while small mosaics with wide joints can use several times more per square foot. This calculator estimates bags from your tile format and joint dimensions.

What this number means

Grout use is governed by how much joint there is, not just how much floor. Every tile edge is a joint, so halving the tile size roughly doubles the joint length per square foot — which is why a mosaic floor can use three times the grout of a large-format floor at the same joint width.

The weight above is the mixed grout the joints will actually hold, plus your waste allowance for what stays in the bucket and gets washed off. Bag counts round up, and it is always worth finishing a job from one bag and one dye lot rather than mixing batches.

The formula

Joint volume per tile ≈ ((Tile width + Tile length) × Joint width + Joint width²) × Joint depth
Tiles per sq ft = 144 ÷ ((Tile width + joint) × (Tile length + joint))
Total volume = Joint volume per tile × tiles per sq ft × area in sq ft
Weight = Volume × 0.077 lb per cu in (sanded) or 0.070 (unsanded), then × (1 + waste %)
Bags = Weight ÷ bag size, rounded up

Worked example

100 sq ft of 12×12 floor tile, 1/8 in joints. Tile thickness and joint depth are 3/8 in, grout is sanded.

Joint volume per tile = ((12 + 12) × 0.125 + 0.016) × 0.375 ≈ 1.13 cu in
Tiles per sq ft = 144 ÷ 147.02 ≈ 0.98 → total joint volume ≈ 111 cu in
Weight = 111 × 0.077 ≈ 8.5 lb; with 10% waste ≈ 9.4 lb
That is one 25 lb bag (or one 10 lb bag, with almost nothing spare)

The same 100 sq ft in 2 in mosaic needs roughly three times as much — joint length, not area, is what you are buying.

Assumptions and limitations

Density figures are for standard cementitious grout mixed to manufacturer consistency. High-performance and epoxy grouts have different yields — check the bag's coverage table for those.
Joints are assumed struck to the full joint depth. Deeply raked or bevelled-edge joints hold less; the estimate errs on the safe side.
Manufacturer coverage charts for the same tile format can differ by 20% between brands. Treat this as a planning figure and keep the receipt — unopened bags are returnable.
Movement joints (perimeter and over fixtures) should be filled with flexible sealant, not grout, and are not part of this estimate.