Grout is the most commonly under-ordered material in tiling. Homeowners calculate tile perfectly, then stand in the aisle guessing at grout — and either run short mid-job or pay for three bags they’ll never open. Grout quantity depends on four variables, and once you have them the math is quick.
Estimate your tile count and layout first with our tile quantity calculator, then size the grout to match.
The Four Variables
- Tile dimensions (e.g. 30 × 30 cm)
- Joint width (2 mm for rectified porcelain, 3–5 mm for ceramic, 6–10 mm for large stone)
- Tile thickness (the deeper the tile, the more grout fills the joint)
- Total area in square metres or feet
Coverage Rule of Thumb
For a 300 × 300 mm tile with a 3 mm joint, one 5 kg bag of cementitious grout covers roughly 4–5 m². Coverage scales strongly with joint width and inversely with tile size:
| Tile size | Joint | Approx coverage per 5 kg |
|---|---|---|
| 100 × 100 mm | 3 mm | ~1.5 m² |
| 300 × 300 mm | 3 mm | ~4.5 m² |
| 600 × 600 mm | 3 mm | ~9 m² |
| 600 × 600 mm | 6 mm | ~5 m² |
| 300 × 600 mm | 10 mm | ~2 m² |
Notice how a 100 × 100 mm mosaic uses about six times more grout per square metre than a 600 × 600 mm tile. Small tiles mean more joints, and joints are where grout goes.
A Worked Example
A 12 m² bathroom floor in 300 × 300 mm ceramic tile with 3 mm joints:
- Coverage ≈ 4.5 m² per 5 kg bag
- Bags = 12 ÷ 4.5 = 2.67
- Add 10% for waste and touch-ups = 2.94 → buy 3 bags
Epoxy and Sanded vs Unsanded
Unsanded grout is for joints under 3 mm and won’t scratch polished stone. Sanded is for joints 3 mm and wider and resists cracking better. Epoxy grout covers roughly 20–30% less per unit than cementitious, but it doesn’t need sealing and resists staining — worth the extra for kitchens and wet areas.
FAQ
How much extra should I buy? 10% for a straightforward floor, 15% if you’re mixing colours or working around many fixtures.
Does a bigger trowel notch use more grout? No — notch size controls adhesive, not grout. Grout fill is set by joint width and tile depth.
Can I store leftovers? Cementitious grout keeps about 6–12 months if sealed and dry. Epoxy has a shelf life; check the date.
Fewer, larger tiles and tight joints are the two levers that cut grout use fastest. Size the joints to the tile, then buy by coverage — not by guess.
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