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Jointing Sand Calculator
Calculate kiln-dried or polymeric jointing sand for paving joints.
Total area of the paving, measured across the top including joints
Size of each block or slab — smaller units have more joints, so use more sand
Gap between units — 2–5mm for block paving, up to 10mm for slabs
Joint depth to fill — usually the full block depth (50–80mm); 25mm+ for slabs
Kiln-dried suits block paving; polymeric resists weeds and washout
Extra material for spillage and uneven joints (5-15% typical)
Weight of each bag — standard sizes are 15kg or 20kg
How We Calculate This
This calculator estimates jointing sand from the paved area, the size of each paving unit, the joint width, the joint depth and the sand type.
Coverage rate
For a grid of units measuring a × b (mm) with joint width w, joints run in both directions, so the share of the surface taken up by joints is:
jointFraction = 1 − ((a − w) / a) × ((b − w) / b)
Then kg/m² = jointFraction × jointDepth(mm) × sandDensity(kg/L). Smaller units (block pavers) have far more joint length per m² than large slabs, so they need more sand. Wider and deeper joints also need more.
Sand types
- Kiln-dried: Fine, dry silica sand swept into block-paving joints (≈1.5 kg/L). Cheapest option but can wash out and needs topping up.
- Polymeric: Hardens when wetted, resisting weeds and washout (≈1.6 kg/L). More expensive but long-lasting; needs joints ≥3mm wide and ≥25mm deep.
- Silver sand: Very fine grade, good for narrow joints under 3mm and tight slab gaps.
Frequently Asked Questions
Sand needed = paved area × joint plan-area fraction × joint depth × sand density. The joint fraction depends on your paving unit size: for a grid of units measuring a × b (mm) with joint width w, fraction = 1 − ((a−w)/a) × ((b−w)/b), because joints run in both directions. Smaller units (block pavers) have far more joint length per m² than large slabs, so they use more sand.
For standard 200 × 100mm block pavers with 3mm joints filled to full 50mm depth, roughly 3.3 kg/m² — so a 20kg bag covers about 6 m² of new paving. Deeper 80mm blocks rise to about 5–6 kg/m². Re-sanding cleaned existing paving uses much less because joints are only partly empty.
Yes, 5–10% extra is recommended. Kiln-dried sand is swept in dry and a fair amount blows away or stays on the surface, and joints settle after compaction so they need topping up.
Polymeric sand contains a binding agent that hardens when wet, locking pavers in place and resisting weed growth and ant nests. It is more expensive than kiln-dried sand but much more durable. Joints generally need to be at least 3mm wide and 25mm deep for it to cure properly.
Make sure the paving and joints are bone dry. Tip kiln-dried sand over the surface and sweep it into the joints with a stiff broom, working diagonally across the paving. Vibrate or compact, then re-sweep and top up until joints are full and level. For polymeric sand, brush in, remove all excess from the surface, then activate with a fine mist of water following the product instructions.
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Last updated: February 2026
All calculations are estimates based on standard gardening guidelines. Results may vary with soil conditions, climate, and plant varieties.