Pick a typical pad or enter your own size. You get bags, cubic yards, and the gravel and rebar for the base, all on one ticket you can print.

Pad sizes at a glance

Worked out with this calculator: 10% extra concrete and a 4 inch gravel base. Thickness is a starting point, so change it to suit the load.

Pad	Thick	Cubic yards	80 lb bags	60 lb bags	Gravel (tons)	Bags or truck
AC unit 3 × 3 ft	4 in	0.12	6	8	0.2	Bags
Generator 3 × 5 ft	4 in	0.20	10	13	0.3	Bags
Grill area 6 × 6 ft	4 in	0.49	22	30	0.7	Bags
Shed 8 × 10 ft	4 in	1.09	49	66	1.5	Compare quotes
Shed 10 × 12 ft	4 in	1.63	74	98	2.3	Compare quotes
Hot tub 8 × 8 ft	6 in	1.30	59	79	1.2	Compare quotes

How to size a pad

Footprint: measure the shed or equipment base, then add the edge allowance its instructions ask for.
Thickness: 4 inches for light loads; thicker for heavy or concentrated loads such as a filled hot tub.
Base: a compacted gravel layer under the pad. Turn on Gravel base under Order options to add it to the ticket.
Reinforcement: for larger pads, add a rebar grid under Order options to get the number of 20 ft bars.

Cubic yards = length (ft) × width (ft) × thickness (in ÷ 12) ÷ 27

Worked example: hot tub pad

An 8 × 8 ft pad, 6 in thick, with a 4 in gravel base and an 18 in rebar grid. The ticket gives 1.30 cubic yards of concrete (59 bags of 80 lb), 1.2 tons of gravel and 5 × 20 ft rebar bars. A filled hot tub is a heavy, concentrated load, so use the thickness and reinforcement the hot tub maker specifies.

Forming and pouring a pad

Lay it out and square it. Stake the corners, then check that the two diagonals are equal.
Dig to the pad thickness plus the gravel base.
Add the gravel and compact it level.
Set the forms. A 2×4 is 3½ in tall and a 2×6 is 5½ in, so a "4 in" pad formed with 2×4s is really 3½ in unless the forms sit higher. Enter the real thickness. Give the top a slight fall away from buildings.
Place reinforcement on chairs so it sits in the slab, not on the gravel.
Pour, screed, float and edge, then keep it damp while it cures, as the bag directs.

Common mistakes

Making the pad exactly the size of the equipment, when the instructions ask for clearance around it.
Ordering for the nominal thickness of the form boards instead of their actual height.
Forgetting the gravel base when planning the dig depth.
Pouring from bags in batches that set at different times; on bigger pads compare a ready-mix quote.

Questions

How many bags of concrete do I need for a 4 × 4 pad?

At 4 inches thick with 10% extra, a 4 × 4 ft pad takes 10 bags of 80 lb mix or 14 bags of 60 lb mix (0.22 cubic yards).

How many bags for a 10 × 10 pad?

At 4 inches thick with 10% extra: 62 bags of 80 lb mix, or 1.36 cubic yards. At that size, compare the bag cost with a ready-mix delivery quote.

How thick should a concrete pad be?

4 inches is the usual minimum for light-duty pads such as AC units, grills and garden sheds. Heavier loads (a filled hot tub, a vehicle, a large workshop) need a thicker pad. Follow the equipment maker’s install guide and your local code.

Do I need gravel under a concrete pad?

A compacted gravel base helps drainage and gives an even surface to pour on. Pick a depth under Order options and the ticket adds the gravel in cubic yards and tons.

Should the pad be bigger than the shed or equipment?

Often, yes: the shed kit or equipment instructions usually state the pad size or the clearance they want around the base. Use their figure, then enter the pad size here.

Can I combine a pad with footings or post holes?

Yes. Use “+ Add a part” to add a footing, post holes or steps, and the ticket totals everything into one order.

Guides: How thick should a slab be? · Gravel base under a slab

Sources

Bag yields: QUIKRETE Concrete Mix No. 1101 data sheet. Gravel weight: 1.4 tons per cubic yard (SelectSG: crushed stone 1.35–1.4). Rebar grid method: Inch Calculator.

Concrete Pad Calculator