How Much Grout Do I Need?
Tile size is the biggest driver of how much grout a job needs — smaller tiles pack far more joint length into the same floor area than large ones. The table below shows grout weight by tile size for a fixed 100 sq ft floor at standard joint dimensions; for your own tile size, area, and joint width, the grout calculator computes the exact figure. This page is the size comparison itself, plus a worked example isolating what joint width alone does to the total.
Grout needed by tile size (100 sq ft floor)
Figures assume a 3/8in joint depth, a 1/8in joint width, standard sanded cementitious grout at 1,700 kg/m³, and the standard 10% waste allowance — the same assumptions as the calculator's own worked examples.
| Tile size | Grout needed (100 sq ft) |
|---|---|
| 2 × 2 in mosaic | 45.6 lb |
| 6 × 6 in | 15.2 lb |
| 6 × 24 in plank | 9.5 lb |
| 8 × 8 in | 11.4 lb |
| 12 × 12 in | 7.6 lb |
| 18 × 18 in | 5.1 lb |
| 24 × 24 in | 3.8 lb |
Joint-volume coverage methodology: Custom Building Products grout coverage calculator (Polyblend), consistent with Mapei's published grout coverage method — the 2 in mosaic needs roughly 12x the grout of the 24 in tile for the identical floor area, because joint length per square foot scales with (length + width) ÷ (length × width), which grows fast as tile shrinks. Scale any row proportionally for a different floor area.
A full example: joint width alone, same tile
Tile size dominates the grout estimate, but joint width matters too — and unlike tile size, its effect is exactly linear, not curved. Take the same 100 sq ft floor of 12 × 12 in tile at the standard 3/8in joint depth, and change only the joint width. At the standard 1/8in joint, that floor needs about 7.6 lb of grout. Narrowing to a 1/16in joint — common for rectified porcelain or polished stone, where tile edges are precise enough not to need a wide gap — halves that to about 3.8 lb, since halving joint width simply halves joint volume. Widening to a 1/4in joint — typical for handmade or size-irregular tile that needs a wider gap to absorb dimensional variation — doubles the standard figure to about 15.2 lb. Tile size decides which row of the table above you start from; joint width then scales that starting figure up or down in direct proportion, which is why the calculator treats it as a simple multiplier rather than a lookup.
Tile size and joint width together
Because joint width scales the total in direct proportion, the first table extends to the three joint widths you are most likely to choose. Every figure is for the same 100 sq ft floor at a 3/8in joint depth, with the 10% waste allowance included:
| Tile size | 1/16in joint | 1/8in joint | 1/4in joint |
|---|---|---|---|
| 2 × 2 in mosaic | 22.8 lb | 45.6 lb | 91.2 lb |
| 6 × 6 in | 7.6 lb | 15.2 lb | 30.4 lb |
| 6 × 24 in plank | 4.8 lb | 9.5 lb | 19.0 lb |
| 8 × 8 in | 5.7 lb | 11.4 lb | 22.8 lb |
| 12 × 12 in | 3.8 lb | 7.6 lb | 15.2 lb |
| 18 × 18 in | 2.5 lb | 5.1 lb | 10.2 lb |
| 24 × 24 in | 1.9 lb | 3.8 lb | 7.6 lb |
Read across a row to see what a joint-width decision costs in grout, and down a column to see what tile size costs. A 2 × 2 in mosaic at a 1/4in joint needs about 48 times the grout of a 24 × 24 in tile at 1/16in on the same floor. That gap is why a mosaic job can run out of grout while the same bag would have finished a large-format floor.
Wall tile: a subway-tile shower
Wall tile is usually thinner than floor tile, so its joints are shallower and hold less grout per square foot, even though subway and other small wall tiles have a lot of joint length. Take a 60 sq ft shower surround in 3 × 6 in subway tile, 1/4in thick, with a 1/16in joint. Joint depth is the tile thickness, so the joint network holds (3 + 6) ÷ (3 × 6) × 1/16 × 1/4 in of grout per square inch of wall. Over 60 sq ft that is about 67.5 cubic inches, or roughly 1.9 kg (4.1 lb) at the table's density, and about 4.6 lb with the 10% waste allowance. That is less than the 7.6 lb a 12 × 12 in floor of 100 sq ft needs, because the thin tile and fine joint more than cancel out the smaller tile size. Enter wall tile at its real thickness in the calculator; using a floor-tile depth by habit overestimates a thin wall tile by half or more.
Regrouting an existing floor
Regrouting doesn't replace the full joint. The old grout is raked or ground out to a partial depth, and only that depth is refilled. Whatever depth you actually remove is the figure to enter as joint depth, not the tile thickness. Raking the 12 × 12 in floor above down by 1/8in, a third of its 3/8in depth, needs about a third of the grout: roughly 2.5 lb per 100 sq ft instead of 7.6 lb. Measure the cleaned-out joints in a few places before buying, since worn joints near doorways are often deeper than the rest.
When the estimate runs short
The joint-volume method assumes every joint is the width you planned and exactly as deep as the tile. Real floors drift from that in two directions. Handmade tile, reclaimed tile and natural stone with irregular edges end up with joints wider than the spacers in places, so the grout used runs above the estimate. Tile with rounded, cushioned edges has shallower joints at the surface than the tile's thickness suggests, so it uses a little less. If your tile has irregular edges, measure a few of the widest joints once the tile is set and re-run the estimate with that width before buying the last bag.