Paver Base Calculator: Stone Depth for Clay and for Sand

The subgrade decides this job. On the sand and gravel outwash under most of Long Island, water leaves quickly and a 4 inch base does what it is asked. On the silt and clay valley floors of the Hudson and the Mohawk, and on the flat lake-plain clay west of Syracuse, the same 4 inches sits on ground that holds water all winter and heaves when it freezes. Pavers do not fail because of the pavers. They fail because of what is under them, and the paver base calculator only sizes the layer once you have decided how thick it needs to be for your ground.

Thaw to leaf-fall: when a base can actually be compacted

There is a working season for this, and it is set by the ground rather than the calendar. Frozen ground will not compact at all, so winter is out across the state. The weeks straight after the thaw are little better on clay: saturated subgrade pumps under a plate compactor instead of tightening, and the base you roll in a wet April will move again in June. On Long Island and around the city the milder coast opens the season earlier and closes it later, but a cold snap or a week of nor'easter rain still stops the work.

The practical stretch is from a few weeks after the frost is out until the ground starts to lock up in late autumn. Order the stone when the excavation is done, not before, because a pile sitting on turf for two weeks kills the grass under it.

Marking the base 6 inches past every open edge

The base is bigger than the patio. Extend it 6 inches beyond every edge that is not against a wall, so the edge restraint is sitting on compacted stone rather than on lawn soil. That overhang is the single most-missed number on this page, and on a small patio it adds a surprising share of the total.

Take a hypothetical patio 16 ft along the house by 13 ft out from it, with three open sides. The paved surface is 208 square feet. The base footprint is 16 plus 6 inches at each open end, by 13 plus 6 inches at the outer edge: 17 by 13.5 ft, or 229.5 square feet. That is the area the calculator wants.

Entering compacted inches, not the depth of the hole

Put in the compacted thickness of the stone layer alone. Not the excavation, not the stone plus the sand plus the paver. Choose rectangle, circle by diameter, or multiple areas to total up to five shapes, which is how a patio plus the path leading to it goes in as one calculation. Feet for length, width and diameter; inches for depth, from 0.25 to 24. Select the material so the tonnage is right, leave the 10% extra for compaction and spillage ticked, and the result returns cubic yards, tons and cubic feet at once, with the option to email it to yourself.

The dig depth is separate arithmetic, and worth marking on a stake before the spade comes out:

Excavation = base + 1 in bedding sand + paver thickness, less whatever you want standing above grade

For the example patio at 6 inches of base, with a 2 3/8 inch paver set half an inch proud of the lawn: 6 + 1 + 2 3/8 = 9 3/8 inches, less the half inch reveal, so dig about 8 7/8 inches below the existing grade. Overdigging costs twice, once in soil to haul away and once in stone to bring the level back up.

Where the weight comes from

Base stone is the heavy part of a patio order. This site publishes crusher run and Item 4 at about 3,000 lb per cubic yard, or 1.50 tons per yard; the bedding sand above it runs about 2,700 lb, or 1.35. Same patio, same square footage, two different conversions, which is why the two layers are calculated separately and why the base is usually six or seven times the tonnage of the sand.

Stone and sand are both sold here by the ton, so the tons figure is what the product page wants. The cubic yard figure tells you what will be sitting in the driveway.

Depths for a walk, a patio and a parking apron on clay

The 16 by 13 ft patio, on clay, at 6 inches:

• base footprint 17 x 13.5 = 229.5 sq ft
• 229.5 x 6 / 12 = 114.75 cu ft
• 114.75 / 27 = 4.25 cu yd
• 4.25 x 1.50 = 6.38 tons
• with the 10% box: 4.68 cu yd, 7.02 tons

A 24 by 3 ft walkway at 4 inches, open on all four sides, so 25 by 4 ft of base:

• 25 x 4 = 100 sq ft
• 100 x 4 / 12 = 33.33 cu ft
• 33.33 / 27 = 1.23 cu yd
• 1.23 x 1.50 = 1.85 tons, or 2.04 with the 10%

Both are illustrations with invented dimensions.

Ordering half a ton long, and building it in 2 inch lifts

Round up. Half a ton of surplus base stone fills a rut or backs up a step; half a ton short means compacting the layer in two sessions, which is how a hollow gets built into a patio on day one. Place it in 2 inch lifts, mist each lift lightly and roll it, and slope the finished base 2 to 3 percent away from the house, because the sand and the pavers will follow whatever grade the base sets.

Build the structural depth out of Crusher Run or Item 4. Stone Dust belongs on top of a compacted base as a thin screed layer, not as the base itself; used alone it holds water and pumps under load through a freeze-thaw winter.

Two layers, one delivery

Size the bedding sand on the paver sand calculator, then order the Mason Sand and the base stone together so they arrive on the same truck. For a drive or an unpaved pad with no edge restraint to carry, the crusher run calculator does the same arithmetic without the overhang. Delivery is arranged at checkout by ZIP code, and the driver needs a clear route and a firm place to tip.

Common questions

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