Tile Grout Calculator

The short answer

Grout volume is the joint area: tile area divided by tile size, times joint width, times joint depth. In practice, a 25-pound bag of sanded grout typically covers 80 to 120 square feet of 12-inch tile with eighth-inch joints. The same bag covers far less on small mosaic tile or with wider joints, because the joint area multiplies as tile size falls.

What it depends on

Tile size and joint width are the two inputs that matter, and both are easy to get wrong. Large-format tile with tight joints uses very little grout per square foot, while small format with wide joints uses a lot. Sanded versus unsanded grout is a joint-width decision, not a preference: unsanded is used on narrow joints to avoid scratching, sanded on wider ones for strength.

Where this stops being useful

This is a quantity estimate. Substrate flatness, tile Lippage, movement joints and the manufacturer's specified grout type all affect both the material and the outcome. Wet-area assemblies have waterproofing requirements that the grout does not satisfy on its own. General information and planning only, not engineering, structural or code advice.

Grout quantity is a function of joint width as much as area, and the relationship is not linear. Halving the joint width roughly halves the grout, but doubling the tile size does not halve it — larger tiles create fewer joints, and the saving comes from that rather than from area. The bag states coverage for a standard joint width and a standard tile size, so if your joint is narrower or your tile larger, the stated coverage overestimates what you need. Work out the actual joint length on a small sample rather than trusting the printed figure.

Grout is worth calculating properly for two reasons. The first is cost, which is small. The second is that a shortage discovered halfway through a tiled floor means a visible colour difference between batches, and that shows for the life of the floor.

Grout colour and width are decided at installation and cannot be changed later without removing the tiles, so settle them before the adhesive goes down. Sealing is a separate question — cement-based grout needs sealing, epoxy grout does not, and the two are not interchangeable. Order the grout at the same time as the adhesive and the tiles; running out mid-job means a second trip and a risk of a slightly different batch in the same floor, which shows.

Grout fills the gaps between tiles, and the amount you need depends on how much gap there is rather than how big the floor is. Two rooms of the same size can need very different quantities: large tiles with narrow joints leave little space to fill, while small tiles with wide joints leave a lot. That is why grout is estimated from tile size and joint width, not from area alone. The dominant variables are tile size and joint width. Small tiles create many more joints per square foot, so they consume far more grout — halving the tile size roughly doubles the joint area. Wide joints need more grout per joint. The thickness of the tile also matters, because the joint is as deep as the tile is thick, and a thick stone tile needs a deeper fill than a thin ceramic one. Water content, application technique and waste all shift the real figure. Some grout is lost to sponging off the surface, some sticks to the float and bucket, and mixing more than you can apply in one go leaves unused material that sets hard. Buying a little more than the calculator suggests is normal practice, and any surplus keeps for future repairs if stored dry and sealed. This calculator applies the standard estimator — joint cross-section times joint length per unit area — and returns kilograms for your tile dimensions, then converts to bags. It assumes an even joint and a single grout type, and it does not distinguish sanded from unsanded grout, which differ in density. Treat the result as a shopping estimate and check the coverage table on your chosen grout.

This calculator returns estimates for planning and general information only. It is not engineering, architectural, structural, electrical or code advice, and it cannot replace a qualified professional who has seen the site. Material quantities depend on the actual dimensions, the product you buy and local building codes, so confirm the figures before ordering materials or starting work, and always follow local regulations.