Grout Calculator — Bags, Coverage & Joint Width
Calculate how much grout you need for any tiling job. Enter tile size, joint width and tile thickness to get the exact quantity in kg — accounting for tile perimeter, grout density and the specific formula used by professional tilers.
How much grout do I need?
It follows joint length, not floor area, so smaller tiles need far more of it. The sum is ((tile length + width) ÷ (length × width)) × joint width × tile thickness × 1.7. A 300 mm square tile at a 3 mm joint works out near 0.34 kg/m² — about 0.07 lb/sq ft — where a 600 mm tile needs roughly half that over the same floor.
What joint width should I use?
Rectified porcelain will take 2–3 mm, about ⅛ in; pressed ceramic and handmade tiles need 3–5 mm — ⅛ to 3/16 in — to absorb their size variation. Outdoors and on large-format tiles, go wider: the joint is what accommodates movement, and closing it up is how tiles come loose.
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How the grout calculator works
- 1Grout kg/m² = ((L+W) ÷ (L×W)) × joint width (mm) × tile thickness (mm) × grout density (1.7 kg/dm³, about 106 lb/cu ft)
- 2Where L = tile length (mm), W = tile width (mm)
- 3This gives the theoretical grout quantity; real consumption varies by tile edge shape, surface texture and cleanup loss
- 4Total grout = grout per m² × total area (m²)
- 5Add 10% waste for end-of-bag losses and corner cuts
- 6Round grout quantity according to the pack size used in the shared tile calculator or the actual product packaging; verify 2 kg, 5 kg or 25 kg availability locally — US packs are usually 10 lb or 25 lb
Worked example
20 m² (215 sq ft) of 300×300 mm (12 × 12 in) tiles, 10 mm thick, 3 mm (⅛ in) joint width.
Grout per m²: ((300+300) ÷ (300×300)) × 3 × 10 × 1.7 = 0.34 kg/m². Total: 0.34 × 20 = 6.8 kg + 10% = 7.5 kg, about 17 lb → two 5 kg bags.
Frequently asked questions
What grout joint width should I use?
Rectified (precision-cut) tiles: 1.5–2 mm, under ⅛ in. Standard ceramic tiles: 3–5 mm (⅛–¼ in). Natural stone and rustic tiles: 5–10 mm (¼–⅜ in). Check the tile manufacturer's recommendation — minimum joint widths are specified to allow for dimensional variation.
What is the difference between sanded and unsanded grout?
Unsanded (fine) grout is used for joints up to 3 mm, or ⅛ in — it shrinks less in narrow joints. Sanded grout contains fine aggregate and is used for joints 3–15 mm (⅛–⅝ in) — the sand prevents shrinkage cracking in wider joints.
How long after tiling can I grout?
Wait for the adhesive minimum open time specified on the datasheet — typically 24 hours for standard adhesives, 4–6 hours for rapid-set. Grouting too soon can disturb tiles before the adhesive has bonded.
Can I use epoxy grout instead of cement grout?
Epoxy grout (class RG) is more stain-resistant, non-porous and stronger than cement grout — ideal for commercial kitchens, pools and shower enclosures. It is harder to apply, must be used quickly and costs 3–4× more than cement grout.
How do I seal grout?
Apply a penetrating grout sealer 7–14 days after grouting, once the grout has fully cured. Reapply annually in high-use areas such as showers and kitchen floors. Epoxy grout does not require sealing.
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