Coverage charts on the bag assume a paver size you probably aren't using. This works out the real volume of your joints from the paver dimensions, so the answer matches your patio rather than the example on the packaging.
Polymeric sand does not cover an area. It fills the joints between the pavers, and how much joint there is depends entirely on the size of the paver.
Small pavers have far more joint per square foot than big ones, because there are more of them and every one has a perimeter. Run the numbers at a quarter-inch joint and the difference is stark:
| Paver | Share of area that is joint |
|---|---|
| 4 × 8 in | 8.73% |
| 6 × 9 in | 6.59% |
| 12 × 12 in | 4.04% |
| 24 × 24 in | 2.05% |
A patio of 4 × 8 pavers needs more than four times the sand of the same patio laid in 24 × 24 slabs. The chart printed on the bag picks one paver and one joint width and prints a single number — which is right for that combination and wrong for everything else.
A paver of length L and width W laid with a joint of width j occupies a cell of (L+j) × (W+j). The paver itself covers L × W of that, and everything left over is joint. So the joint share of the area is one minus L×W divided by (L+j)×(W+j).
Multiply that share by the paved area and by the joint depth, and you have the volume of sand needed. Convert with the weight of the bag and you have a bag count that reflects your patio rather than an example.
Below about an eighth of an inch, polymeric sand generally cannot get down the joint. The polymer-coated grains bridge at the surface instead, and what looks like a filled joint is hollow underneath. Some products are formulated for tighter joints, so check the bag before assuming.
Depth matters just as much and gets less attention. Fill less than an inch and there is not enough mass in the joint to hold together — the first heavy rain washes it out and takes your afternoon with it. An inch and a half is the usual target, stopping about an eighth of an inch below the paver surface so the sand is not sitting proud where a broom will catch it.
Sweep it in dry, in several passes, vibrating or tamping between them so the joints settle and take more. Then sweep the surface properly clean — polymer left on the paver face hardens into a haze that is genuinely difficult to remove.
Water it exactly as the bag says. Under-watering leaves it powdery; over-watering floats the polymer out of the joint and up onto the surface. And check the forecast, because rain within the curing window can undo the whole job.
| Assumption | Value used |
|---|---|
| Bag weight | 50 lb |
| Sand density | 2700 lb/yd³ |
| Minimum workable joint width | 0.125 in |
| Minimum sensible joint depth | 1 in |
| Cubic feet per cubic yard | 27 |
| Default waste factor | 10% |
Bag weights vary between brands, and a few products are sold in 55 lb sacks. The joint-volume maths holds regardless — only the divisor changes.