How Much Concrete for an AC Pad? Sizes and Bag Counts

How much concrete for an AC pad is usually a small number of bags. A 3x3 foot pad poured 4 inches thick needs about 3 cubic feet of concrete, which is about 5 bags of 80-pound mix. A 3x4 foot pad takes about 7 bags, and a 4x4 pad takes about 9. Those counts already round up a little for waste. Before you pour, check the condenser or heat pump manual for pad size, clearances, and whether the maker wants the unit raised above grade.

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Bag counts for common pad sizes

Pad size	Volume at 4 in	80-lb bags	60-lb bags
2.5 x 3 ft	2.5 cu ft	5	6
3 x 3 ft	3.0 cu ft	5 to 6	7
3 x 4 ft	4.0 cu ft	7	9
4 x 4 ft	5.3 cu ft	9 to 10	12 to 13
4 x 6 ft (two units)	8.0 cu ft	14	18

These use about 0.6 cubic feet per 80-pound bag and 0.45 per 60-pound bag. The concrete calculator can size an odd shape.

How big should the pad be?

Make the pad a few inches larger than the unit’s footprint on every side. Many residential condensers sit in roughly 24 to 36 inch squares, so a 3x3 or 3x4 pad is common. Leave room for service access and for the clearances the manufacturer lists, which often include space around the coil and above the fan. If you may upgrade to a larger heat pump later, a slightly bigger pad costs only a bag or two more.

Thickness and height

Four inches of concrete is typical for a residential condenser. Many installers set the top of the pad 2 to 3 inches above surrounding grade so the unit stays out of standing water and mulch. In snowy areas, heat pumps are often raised further on brackets or stands so defrost water can drain and snow does not block the coil. Check the installation instructions.

Base under the pad

Dig down so you can put 2 to 4 inches of compacted gravel under the slab. A 3x3 pad needs less than a cubic foot of base, so a couple of bags of paver base or all-purpose gravel is enough. Tamp it firm and level so the pad does not tilt as the soil settles. A tilted pad can make a condenser vibrate and strain the refrigerant lines.

Poured concrete vs precast and plastic pads

Poured concrete: heaviest and most stable; good when you want a custom size or a pad for two units.
Precast concrete pads: sold at supply houses; quick to set on a gravel bed.
Composite or plastic pads: light, do not crack, and are common in new installs; they rely on a well-compacted base.

Many HVAC contractors bring a composite pad as part of a replacement, so ask before you pour.

Pouring tips for a small pad

Build a simple 2x4 form and check it for square and level.
Slope the top very slightly, about 1/8 inch per foot, away from the house.
Mix bags to a stiff, workable consistency rather than soupy.
Tool the edges and give the top a broom or float finish.
Let it cure at least several days before the unit goes on, longer in cool weather.

Bottom line

An AC pad usually takes 5 to 10 bags of 80-pound concrete: about 5 for a 3x3 pad, 7 for 3x4, and 9 to 10 for 4x4 at 4 inches thick. Size it a few inches larger than the unit, set it on compacted gravel, keep it slightly above grade, and confirm clearances in the equipment manual.

Questions people ask

How many bags of concrete for a 3x3 AC pad?

About 5 bags of 80-pound concrete at 4 inches thick, or about 7 bags of 60-pound mix.

How thick should a concrete AC pad be?

About 4 inches is typical for residential condensers, set on 2 to 4 inches of compacted gravel.

How big should a pad be for an outdoor AC unit?

A few inches larger than the unit on each side, with room for the clearances in the installation manual.

Can I use a plastic AC pad instead of concrete?

Yes. Composite pads are common and work well on a firm, level gravel base.

How long should an AC pad cure before setting the unit?

Give it several days at minimum, and longer in cool weather, before setting a heavy condenser on it.

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