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.