A paver patio is four materials, not one
People order pavers and forget that the pavers are the thin part. Under a finished interlocking concrete pavement sit three more materials, and two of them are heavier than the pavers themselves: a compacted aggregate base that carries the load into the subgrade, a screeded bedding course of coarse sand that the units are set into, and jointing sand that fills the gaps and creates the interlock the whole system depends on. Around the outside runs an edge restraint, without which the field simply spreads and the joints open.
Each layer is sized by a different rule. The paver count comes from geometry: the paved area divided by the footprint one unit occupies including its joint. The base is sized by traffic and subgrade, not by area. The bedding course is a fixed nominal thickness — 1 in — and treating it as a levelling layer is the classic way to ruin a patio. The joint sand follows from the joint width and the paver thickness, because you are filling a volume, not covering a surface.
Getting the paver count right is worth care for a second reason: colour. Concrete pavers are batched, and a top-up order weeks later can arrive a visibly different shade. Ordering the cut allowance up front, and pulling from several pallets as you lay, is how you avoid a patchy finish.
The module, the joint and why nominal sizes lie
The count formula divides the field area by the module area — the paver plus one joint on each of two adjacent sides. A paver sold as "4 × 8" almost never measures 4 × 8. The common Holland stone is 3⅞ × 7⅞ in, and with a ⅛ in joint the module comes back to exactly 4 × 8 = 32 in². That is deliberate: the manufacturer sizes the unit so that the repeating module lands on a round number and the pattern lays out on a grid. Enter the actual unit size and the joint separately and the arithmetic takes care of itself.
Multiplying the field area by 144 converts square feet to square inches so it can be divided by a module in square inches. Then the cut allowance is applied and the result rounded up to a whole unit. Around 5% covers the perimeter cuts on a rectangular field laid in running bond. A 45° herringbone pattern needs closer to 10%, because every course meets the perimeter at an angle and each cut wastes most of a unit.
The joint share falls out of the same two numbers. The fraction of the surface that is joint rather than paver is one minus the paver face area over the module area. For 3⅞ × 7⅞ units on a ⅛ in joint, that is 1 − 30.516 ÷ 32 = 4.64%. Multiply by the area, by the depth the sand fills, and by roughly 100 lb per cubic foot for dry graded sand, and you have the weight to buy. Working from volume rather than from a manufacturer's coverage claim is the only way to stay accurate when your joint width or paver thickness is not the one the bag was rated for.
Base and bedding volumes are ordinary area-by-thickness calculations, with one wrinkle: the base extends 6 in beyond the paver edge on every side so the edge restraint has something solid to spike into. That is why the calculator computes base volume over a footprint 1 ft larger in each direction than the paved field.
Worked example: a 20 ft × 14 ft patio in 4 × 8 Holland stone
A rectangular patio 20 ft by 14 ft, laid in 3⅞ × 7⅞ × 2⅜ in pavers with ⅛ in joints, on 6 in of compacted base and 1 in of bedding sand, with a 5% cut allowance.
- Paved area. 20 × 14 = 280 ft² = 40,320 in².
- Module area. (7.875 + 0.125) × (3.875 + 0.125) = 8.000 × 4.000 = 32.00 in².
- Pavers before waste. 40,320 ÷ 32 = 1,260 units exactly.
- With 5% cuts. 1,260 × 1.05 = 1,323 → order 1,323 units.
- Base footprint. (20 + 1) × (14 + 1) = 315 ft².
- Base volume. 315 × (6 ÷ 12) = 157.5 ft³ ÷ 27 = 5.833 yd³, which at 2,800 lb/yd³ is 5.833 × 1.4 = 8.17 tons.
- Bedding sand. 280 × (1 ÷ 12) = 23.33 ft³ ÷ 27 = 0.864 yd³, at 2,600 lb/yd³ = 1.12 tons.
- Joint share. 1 − (7.875 × 3.875) ÷ 32 = 1 − 30.516 ÷ 32 = 4.639%.
- Joint sand. 280 × 0.04639 × ((2.375 − 0.125) ÷ 12) = 2.435 ft³ × 100 lb/ft³ = 243.5 lb ÷ 50 = 5 bags.
- Edge restraint. Perimeter 2 × (20 + 14) = 68 ft ÷ 8 ft lengths = 9 pieces, with 68 spikes at one per foot.
Notice the weights. The pavers cover 280 ft² and the base under them is more than eight tons of stone. That is the real logistics problem on a patio job, and it is why the base tonnage, not the paver count, decides whether you need a machine on site.
How thick should the base be, and how flat does it have to be
Base thickness is a function of two things you cannot see from the surface: how much traffic the pavement carries and how well the subgrade drains. Construction guidance from the Interlocking Concrete Pavement Institute puts a pedestrian patio or walk at roughly 4 in of compacted aggregate over a sound subgrade, and a residential driveway at 6 in or more, with 8–12 in where the subgrade is clay, poorly drained, or subject to deep frost. Those are starting points; a soils report or a local specification beats any general figure.
Compact the base in lifts. A plate compactor works about 3–4 in of dense-graded aggregate at a time, so a 6 in base is two passes, not one. Compacting the whole thickness in a single lift leaves the bottom loose, and that is where the settlement comes from a year later.
The bedding course is where most patios are lost. It is 1 in nominal, screeded, and never compacted before the pavers go down. Every extra fraction of an inch is sand that will migrate under wheel load and let the units rock. If your base is out of level, fix the base. Screeding 2 in of sand to hide a low spot is a repair you will make twice. Standard specifications also call for coarse, well-graded bedding sand meeting ASTM C33 — not mason sand, and not the same product you put in the joints.
Edge restraint is not optional. Without it the perimeter units creep outward under traffic, the joints open, the sand washes out and the interlock is gone. Spike the restraint into the compacted base, which is why the base has to extend past the paver edge in the first place. Compare the base tonnage here against the gravel tonnage calculator if you want to price the aggregate separately, and use the concrete slab calculator if you decide on a poured surface instead.
Pavers per square foot for common unit sizes
| Sold as | Actual size (in) | Module with ⅛ in joint (in²) | Pavers per ft² | Joint share |
|---|---|---|---|---|
| 4 × 8 Holland | 3.875 × 7.875 | 32.00 | 4.500 | 4.64% |
| 6 × 6 | 5.875 × 5.875 | 36.00 | 4.000 | 4.13% |
| 6 × 9 | 5.875 × 8.875 | 54.00 | 2.667 | 3.44% |
| 12 × 12 | 11.875 × 11.875 | 144.00 | 1.000 | 2.07% |
| 6 × 12 | 5.875 × 11.875 | 72.00 | 2.000 | 3.10% |
| 8 × 16 slab | 7.875 × 15.875 | 128.00 | 1.125 | 2.34% |
Actual sizes vary by manufacturer — these are the common North American dimensions where the unit plus a ⅛ in joint lands on a whole-inch module. Always check the spec sheet.
What goes wrong on paver jobs
- Using the nominal size in the arithmetic. A "4 × 8" paver is 3⅞ × 7⅞. Using 4 × 8 as the unit size undercounts by about 4.6% — the joints disappear from the calculation.
- Levelling in the sand instead of the base. A thick bedding course looks flat on day one and ruts within a season. Correct the grade in the compacted aggregate.
- Compacting the base in one lift. Plate compactors reach 3–4 in of dense-graded stone. A 6 in base needs two lifts.
- Skipping the edge restraint or spiking it into soil. The restraint has to bear on the compacted base, which is why the base extends 6 in beyond the pavers.
- Sweeping joint sand into wet joints. Polymeric sand activates with water; loading it into damp joints sets it before it reaches the bottom, and the joint stays hollow.
- Ordering exactly the field count. Perimeter cuts, breakage and a spare handful for future repairs are all real. Under-ordering means a colour-mismatched top-up batch.
- Ignoring drainage. A patio needs about 1–2% fall away from the house; a base that holds water pumps fines up into the bedding course and the surface goes soft.
What the standards actually say
Interlocking concrete pavement practice in North America follows the Interlocking Concrete Pavement Institute's construction guidance, published as ICPI Tech Spec 2, Construction of Interlocking Concrete Pavements (ICPI is now part of the Concrete Masonry & Hardscapes Association). It sets the bedding course at a nominal 1 in of coarse sand meeting ASTM C33, requires compaction of the base in lifts, and requires an edge restraint on all unsupported edges.
The pavers themselves are specified by ASTM C936, which sets minimum compressive strength, maximum absorption and freeze-thaw durability for solid concrete interlocking paving units. If a supplier cannot tell you their units meet C936, that is worth knowing before the pallets arrive.
When a different method or a different surface makes more sense
Sand-set interlocking pavement is one of three ways to build a hard surface, and it is not always the right one. A bituminous- or concrete-set paver system, where units are mortared or set on an asphalt bed, suits roof decks, overlays on existing concrete, and any situation where the base cannot be excavated. It is stiffer, more expensive, and has no self-healing interlock. A poured concrete slab is cheaper per square foot in large open areas and needs no edge restraint, but it cracks on its own schedule and cannot be lifted and relaid to fix a settled corner or reach a buried utility.
The genuine advantage of sand-set pavers is repairability. You can lift twenty units, fix the base, and put the same units back with no visible seam. That is why utilities and municipalities use them over vaults and valve boxes.
If your project is a driveway rather than a patio, size the base at the higher traffic class here and check the excavation quantity with the trench excavation volume calculator for any utility crossings, or compare against a bound surface with the asphalt tonnage calculator. If the patio needs a retaining edge because of grade, the retaining wall block calculator handles the wall.