Estimate concrete for a pad under an AC unit, generator, shed or hot tub. Enter the dimensions and get cubic yards and bag count instantly.
One cubic yard = 27 cubic feet, or about 45 bags of 80 lb concrete.
A concrete pad is a small, flat slab poured as a base for equipment that sits outside. The most common sizes follow the equipment they support. A pad should be 2 to 4 inches wider than the unit on every side, and at least 4 inches thick for light equipment or 6 inches for anything heavy.
| Use | Typical Pad Size |
|---|---|
| AC condenser unit | 3 × 3 ft |
| Portable generator | 3 × 4 ft |
| Hot tub / spa | 8 × 8 ft |
| Garden shed | 10 × 12 ft |
| Trash can enclosure | 4 × 6 ft |
Pick the closest size from the table, add a couple of inches for clearance, then enter those numbers above to get the concrete you need.
Level and compact the ground first, then build a wood form the size of your pad. Add a 3 to 4 inch gravel base for drainage, then pour the concrete and screed it level. A 4-inch pad for an AC unit or generator is standard; a hot tub or shed base should be 6 inches thick and reinforced with rebar or wire mesh.
Most pads are small enough to mix by hand or with bagged concrete — a 4 by 4 foot pad at 4 inches needs only about 8 bags of 80 lb mix. Order about 10% extra to cover uneven ground and spillage.
A 3 by 3 foot pad at 4 inches thick needs about 0.11 cubic yards, or 5 bags of 80 lb concrete. Most AC pads are sized 3 to 4 feet square.
At least 4 inches for light equipment like AC units and generators. Use 6 inches for hot tubs, sheds and anything with real weight.
For a small 4-inch pad under an AC unit or generator, rebar is optional. For a 6-inch pad under a hot tub or shed, add wire mesh or rebar to prevent cracking.
A small pad like a 4 by 4 foot AC base is usually $50 to $150 in materials if you pour it yourself. A contractor-charged hot tub pad can run $500 to $1,200.
A pad is a small slab for equipment — AC units, generators, sheds. A slab is the larger structural floor of a building. The math is identical: length times width times thickness divided by 27.