Paver Base Calculator: Stone Under the Patio, Not Sand
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Patios in this state fail from the bottom. A surface that looked flat in October comes out of the thaw with one corner dropped and three pavers rocking, and the cause is almost never the pavers. It is either too little compacted stone or, more often, sand doing a job stone was supposed to do. Those are two different layers with two different jobs: the base is four or more compacted inches of dense-graded stone and it carries the load, while bedding sand is exactly one inch of screeded setting material and carries nothing. This paver base calculator sizes the first of those, at 1.5 tons per cubic yard. The second has its own tool, and the two should never be merged into one number.
How far past the pavers does the stone have to reach?
Further than the patio. Any edge without a wall or a slab beside it needs the base carried about six inches beyond the paver line, because the edge restraint sits on the compacted base and needs something under it to bear on.
Take a hypothetical patio 17 feet along the house by 13 feet out. The paving is 221 square feet, but the base footprint is 13.5 by 18, which is 243 square feet. That is the number that goes in the length and width fields.
How deep under a patio, and how much deeper over lake-plain clay?
Compacted depth, measured after rolling, not the loose lift you spread:
| Where it goes | Compacted base |
|---|---|
| Walkway or garden path | 4 inches |
| Patio or seating area | 4 to 6 inches |
| Anything cars drive on | 6 to 8 inches |
| Clay or soft subgrade | add 2 inches and a geotextile beneath |
That last row does most of the work in the southeast and around Saginaw Bay, where flat, slow-draining clay stays saturated through the thaw and pushes stone down into the subgrade unless fabric separates the two. On the sandy ground of the west side the subgrade drains faster, but the load does not get lighter.
Frost is the reason none of these numbers can be trimmed. The residential code puts frost depth at 42 inches, and local building officials can require more where winters are colder. No patio base reaches that, and it is not supposed to. What the base does is drain and spread the load so the ground beneath it heaves evenly instead of in one corner.
Dig depth follows from the layers, not from a rule of thumb: base plus one inch of bedding plus the paver thickness, minus whatever reveal you want above the lawn. With a 4-inch base and a standard 2 3/8 inch paver, that is about 7 3/8 inches below the finished surface. Mark it on a stake before the first spade goes in. Digging deep costs twice, once to haul soil out and once to buy stone to put the grade back.
Why does 3 cubic yards come back as 4.5 tons?
Because the material weighs about 3,000 lb a cubic yard. Run the patio above at four inches:
- 243 x 4 / 12 = 81 cubic feet
- 81 / 27 = 3.0 cubic yards
- 3.0 x 1.5 = 4.5 tons
- with the 10 percent allowance: 4.95 tons
Order 5 tons. Dense-graded stone weighs more per yard than clean washed stone, which sits nearer 2,800 lb, because the fines fill the voids rather than leaving them open. Those fines are exactly what lets a base lock up under a plate compactor, and exactly why the same material has no business in a drain.
The tool takes a rectangle, a circle by diameter or up to five areas at once, so a patio, a path to the gate and a landing at the steps go in as one calculation. Feet for the dimensions, inches for depth, anywhere from 0.25 to 24. The result shows cubic yards, tons and cubic feet together, and you can have it emailed.
Is the 10 percent box enough when the base goes in two lifts?
It is an allowance for spillage and settlement, not a substitute for measuring. Leave it ticked, then round the answer up to something a delivery can sensibly carry.
The bigger lever is how the stone is placed. A four-inch base built as two compacted two-inch lifts, each lightly misted before the plate goes over it, ends up denser than the same tonnage dumped and rolled once. Damp dense-graded stone compacts tighter than dry, and this is the one piece of technique that decides whether the patio is still flat after three winters.
Two other things to build in while the base is open: a fall of 2 to 3 percent running away from the house, which the sand and pavers will copy, and the edge restraint set on compacted stone rather than on lawn soil.
21AA, 22A or screenings under the pavers?
- 21AA limestone is the usual structural course here, a dense-graded crushed limestone with fines, named for the MDOT class that describes it. That class name is specification language, not a certification.
- 22A road gravel is the other dense-graded class, with a smaller top size. It works as base too, and it has its own calculator if that is what you are buying.
- Stone screenings belong in a thin leveling layer over compacted base, or as a setting bed in place of sand. Used for the full base depth they hold water and pump under load.
Once the tonnage is settled, take it to the product page - the sand and stone in the catalogue are all sold by the ton - set quantity and a delivery date, and finish at checkout where delivery is arranged by ZIP code. Check what the driver needs to reach the tipping spot before you book. Book the drop for after the digging is done. A pile parked on the lawn for two weeks leaves a dead rectangle you will be reseeding in the fall.
Common questions
Does the one-inch sand bed ride on the same delivery as the 21AA?
Yes, and you should, but size them in separate tools because they use different weights and different depths. Base goes through this page at the compacted depth you chose. Bedding sand goes through the paver sand tool at exactly one inch over the same footprint, including the six-inch overhang. Put both quantities on one delivery and check each line against its own unit before you set the date.
Do I square a curved patio off, or put it through circle mode?
Square the curve off. Draw the smallest rectangle that swallows the whole shape, take the tonnage for that, and accept the offcut, because base stone is one of the few materials where having a little spare is genuinely useful for the path or the shed pad. If the curve is a true half circle, use circle mode and halve the result instead.
The stone under the lifted pavers still looks firm. Can it stay where it is?
Only if the old one has failed. Pull the pavers, sweep off the bedding sand and look at what is underneath. Firm, level, draining stone can stay, and you are then buying a new one-inch sand bed and very little else. Soft spots, hollows or standing water mean the base comes out, because with 42-inch frost depth in this state, leaving a failing base under new pavers just reschedules the problem.
Can the last stretch of base go in thinner to stretch a short load?
You will be tempted to thin the last stretch or top it up with sand, and both create the low corner you were trying to avoid. A base has to be its full depth everywhere or it is not a base. Order to the calculated figure plus the allowance, and if the number sits awkwardly between two sensible quantities, take the higher one.
What makes the tonnage drift once the excavation is open?
Uneven digging, mostly. The figure holds where the depth you entered is the compacted depth and the subgrade is even, and it drifts when the excavation is dug unevenly, since every extra inch of dig has to be filled with stone, and when soft patches swallow material during compaction. Measure the dig in several places against your marked stake, and treat the result as a good working figure rather than a guarantee.
Related calculators
The pavers get the compliments. The base earns them.
Crusher run and screenings by the ton, free delivery, ordered together with your bedding sand.