Concrete Pad Calculator
This concrete pad calculator sizes the concrete for a small pad — an AC condenser, shed, hot tub, or generator base. Enter the pad’s length, width, and thickness and it returns cubic yards, cubic feet, weight, and the number of 40, 60, and 80 lb bags, so you know whether to mix bags or order ready-mix.
How to use this calculator
- Enter the pad length and width.
- Set the thickness — 4 inches for light equipment, 6 inches for a hot tub or vehicle.
- Pick a waste allowance.
- Use the bag count for small pads, or the cubic-yard figure for larger ones.
The formula
A pad is a rectangular slab, so multiply length by width by thickness in feet, then divide by 27 for cubic yards:
Cubic yards = (Length ft × Width ft × Thickness ft) ÷ 27
Worked example. A 4 ft × 3 ft AC pad at 4 inches thick: 4 × 3 × 0.333 = 4 cubic feet, which is 0.15 cubic yards — about 7 × 80 lb bags. That is an easy hand-mix job for one person.
Frequently asked questions
How thick should a concrete pad be?
Four inches suits sheds, AC units, and generators. Step up to 6 inches for hot tubs, vehicles, or heavy equipment so the pad does not crack under load.
How much concrete do I need for a 10 × 10 pad?
A 10 × 10 ft pad at 4 inches thick is about 1.23 cubic yards, or roughly 56 × 80 lb bags. At 6 inches it climbs to about 1.85 cubic yards.
How much concrete for an AC or generator pad?
A typical 3 × 4 ft equipment pad at 4 inches thick needs about 0.15 cubic yards — around 7 × 80 lb bags, which is an easy hand-mix job.
Does a concrete pad need rebar?
For most pads, welded wire mesh or #3–#4 rebar in a grid helps control cracking. It is strongly recommended for hot tub and vehicle pads.