Polymeric Sand Calculator

How do you calculate how much polymeric sand you need?

Work out the volume of the joints, not the patio. Find the share of the surface that is joint, multiply by the area and by the depth you fill, then divide by the volume one bag fills. The calculator does this from your paver size, joint width and paver thickness.

Joint share = 1 − (L × W) ÷ ((L + j) × (W + j))
Joint volume (ft³) = area (ft²) × joint share × (paver thickness − 1/8 in) ÷ 12
Bags = joint volume × (1 + extra %) ÷ fill per bag, rounded up

L and W are the paver’s length and width and j is the joint width, all in inches. The 1/8 in comes from Sakrete’s PermaSand data sheet, which says to fill to within 1/8 in (3.2 mm) of the top of the paver; Alliance Gator’s XP G2 sheet says at least 3 mm below the top.

Where the fill per bag comes from. Manufacturers publish coverage as square feet per bag for a stated paver and joint, not a bag volume. We back-calculated the volume from the Alliance Gator XP G2 chart: its 16 cells (four joint widths, four colours, 200 × 100 × 60 mm pavers) work out to 0.415–0.520 L of joint per kg, a mean of 0.478 L/kg. For a 50 lb bag that is about 0.38 ft³ (10.8 L) of finished joint. This is our estimate, not a manufacturer figure, and colours and brands differ by about ±12% around it. If your bag prints a coverage for your joint and paver, type it in: it overrides the model.

How much does a bag of polymeric sand cover? (chart)

A 50 lb bag covers from under 10 ft² to almost 200 ft², depending on joint width and paver size. Narrow joints and big slabs stretch a bag furthest. The chart is the site’s joint-volume model for 2 3/8 in thick pavers filled to 1/8 in below the top.

Coverage is in ft² per 50 lb bag. For a 40 lb pail multiply by 0.8; for a 20 kg bag by 0.88. For thinner pavers coverage rises in proportion: a 1 3/4 in thick paver fills 1.625 in instead of 2.25 in, so a bag goes about 38% further.

How this checks against the data sheets. Sakrete’s PermaSand sheet gives 30–45 ft² per 40 lb pail at a 1/4 in joint on a 2 in paver, without naming the paver size. The model gives 22.4 ft² (4 × 8 in) and 29.7 ft² (6 × 9 in) for the same pail and joint, at or below the sheet’s low end, so it errs toward buying slightly more. Sika’s EVOLUTION Pro 1 sheet gives 1.7–11.8 m² (about 18–127 ft²) per 22.7 kg (50 lb) bag across joints of 3–25 mm, which brackets most of the chart.

How many bags of polymeric sand for common patio sizes?

This table uses 50 lb bags, 2 3/8 in pavers and 10% extra. Pick the column closest to your paver and joint.

Doubling the joint from 1/8 to 1/4 in on the same 4 × 8 in pavers almost doubles the bags, from 10 to 19 on 400 ft². Measure a few joints with a tape before you shop rather than guessing.

Why joint width matters more than patio size

Polymeric sand fills the gaps only, so the joint share of the surface drives the order. On 4 × 8 in pavers the share rises fast as joints open up:

Small pavers have more joint per square foot than big slabs. A 4 × 8 in paver has 2.25 times the joint length per square foot of a 12 × 12 in slab, which is why the chart’s 12 × 12 row covers more than twice the area at the same joint width.

Tumbled, chamfered or irregular stones hold more sand than the clean rectangle in the formula, because the rounded edges widen the gap at the top. For those, use the next joint width up or the coverage on the bag. Natural flagstone with wide irregular joints is best estimated from the bag chart for “natural stone” joints.

Polymeric sand in metric

The formula is the same in millimetres: joint share = 1 − (L × W) ÷ ((L + j)(W + j)), then volume (m³) = area (m²) × share × fill depth (m).

How do you install polymeric sand so the bags go the right distance?

Fill the joints to full depth, compact, top up, then wet. Both data sheets agree on the order; the details below are from the Sakrete PermaSand and Alliance Gator XP G2 sheets.

1. Dry pavers, dry forecast. PermaSand should go down above 40 °F with no rain forecast within 24 hours, on dry pavers; damp pavers stain.
2. Clean the joints full depth on an existing patio. Do not part-fill with ordinary sand.
3. Sweep in and compact. Run a plate compactor (a rubber pad is recommended on the Gator sheet) so the sand settles, then refill. This settling is what the 10% extra covers.
4. Leave the top gap: within 1/8 in (3.2 mm) of the top for PermaSand, at least 3 mm below for Gator XP G2.
5. Blow or sweep the surface clean before wetting, then water as the bag directs. PermaSand allows foot traffic after 24 hours and light vehicles after 72.

Sand left on the face of the pavers when you wet it sets as a haze, so the cleanup step matters more than an extra bag.

Common polymeric sand estimating mistakes

• Using bedding-sand math. Bedding sand is a full 1 in layer under the pavers; polymeric sand fills only a few percent of the surface. Use the paver sand calculator for the bed.
• Guessing joint width. 1/8 in and 1/4 in look similar but differ by almost 2× in bags.
• Ignoring paver thickness. An 80 mm driveway paver takes about a third more sand than a 60 mm one at the same joint.
• Mixing brands mid-job. Colours and set times differ. Buy enough of one product.
• Taking one coverage for every product. Use the chart on your bag when it lists your joint, and the model here when it does not.

All results are ordering estimates. The product’s own coverage chart and instructions take priority over this calculator.