Estimating a 12 x 16 ft Concrete Patio, End to End
One real project, taken from bare lawn to finished slab, with every quantity worked out the way the calculators on this site do it. Swap in your own dimensions and the method holds.
Calculators used
The project
A 12 × 16 ft patio — 192 sq ft — poured 4 in thick on 4 in of compacted gravel, the standard build for furniture-and-grill duty. Two numbers control everything downstream: 192 sq ft of area and 8 in of total depth (gravel plus slab).
Step 1 — Excavation: 6 cubic yards will leave the site
Dig out the full 8 in over the whole footprint:
192 sq ft × 8 ÷ 12 = 128 cu ft ≈ 4.7 cu yd of soil in the ground.
But soil fluffs when dug — loosened spoil takes up roughly 25% more space than it did in the ground, so plan hauling for about 6 loose cubic yards. That is one 10-yard dumpster with room to spare, or a brutal number of pickup trips. Nobody budgets the dirt, and it is routinely the surprise line of a patio project.
Step 2 — Gravel base: about 4 tons
4 in of crusher run over 192 sq ft, with the 15% compaction allowance the gravel calculator applies:
| Line | Amount |
|---|---|
| Loose volume: 192 × 4 ÷ 12 | 64 cu ft |
| With 15% compaction allowance | 73.6 cu ft = 2.73 cu yd |
| Crusher run at 1.50 tons per yard | about 4.1 tons |
Compact it in two 2-in lifts with a plate compactor (a one-day rental), not one 4-in lift. The base, not the concrete, is what decides whether the slab cracks — the same principle as the paver base rule.
Step 3 — Concrete: this is a truck, not bags
4 in of concrete over 192 sq ft, with 10% waste:
192 × 4 ÷ 12 = 64 cu ft; ×1.10 = 70.4 cu ft = 2.61 cu yd.
In 80 lb bags that is 70.4 ÷ 0.60 = 118 bags — nearly 4.8 tons of mixing by hand against a clock, since a slab wants to be one continuous pour. This is far past the half-yard solo limit: order 2.75 yd of ready-mix (suppliers batch in quarter yards) and expect a short-load fee below their minimum. The concrete calculator makes the same call at these numbers.
Step 4 — Forms and finishing kit
The perimeter is 2 × (12 + 16) = 56 linear ft of 2x4 form board, staked about every 2 ft — call it 28 stakes — plus a straight 2x4 longer than 12 ft for screeding. Slope the forms about 1/8 in per foot away from the house so the slab sheds water.
The shopping list
| Item | Quantity | Note |
|---|---|---|
| Spoil hauling | ~6 loose cu yd | Dumpster or haul-away |
| Crusher run | 4.1 tons | Delivered; two compacted lifts |
| Ready-mix concrete | 2.75 cu yd | 4 in slab, 10% waste included |
| 2x4 form lumber | 56 lf + screed | Reusable afterwards |
| Form stakes | ~28 | Every 2 ft |
| Plate compactor | 1 day rental | Base compaction |
| Bull float, edger, groover | rent or borrow | Finishing |
Price it by taking this table to your local suppliers: patio cost is dominated by the concrete line, and the cost-structure guide breaks down where the rest goes.
The clock after the pour
Concrete sets in hours but cures for weeks: keep foot traffic off for 24 to 48 hours, furniture off for about a week, and do not let it dry out fast in hot wind — full design strength arrives around 28 days. The cure-time guide has the full schedule.
Frequently asked questions
Can I pour a 12x16 patio from bags?
It is 118 bags of 80 lb mix — nearly five tons to carry and mix while the first batches stiffen. A ready-mix truck delivering 2.75 yards is the realistic choice; bags make sense below about half a cubic yard.
Do I really need the gravel base?
On well-drained, undisturbed soil a slab can go on grade, but 4 inches of compacted gravel drains water away from the slab, evens out soft spots and is cheap insurance against cracking. Skipping it saves one line of the budget and risks the biggest one.
How long before I can use the patio?
Walk on it after 24 to 48 hours, place furniture after about a week, and give it a month before anything heavy. Concrete reaches most of its strength in the first week but keeps curing for about 28 days.