Concrete AC Pad Calculator
Size a poured concrete pad for an outdoor AC condenser, heat pump, or mini-split unit.
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Short answer
A typical residential AC condenser pad is 30×30 inches and 4 inches thick, which needs about 0.2 cubic yards of concrete — roughly 8 to 10 bags of 80 lb premix. Bigger units, commercial equipment, or pads poured on soft soil should be sized up and may need wire mesh reinforcement.
Typical AC pad sizes by unit capacity
| Unit size | Recommended pad | Thickness |
|---|---|---|
| Up to 2 tons (mini-split, small window unit) | 24×24 in | 3–4 in |
| 2.5–3.5 tons (typical residential) | 30×30 in | 4 in |
| 4–5 tons (larger residential) | 34×34 to 36×36 in | 4 in |
| Commercial / rooftop package units | 36×48 in or larger | 4–6 in |
How to size and pour an AC pad
- Measure the base footprint of the condenser unit, including any mounting feet or brackets.
- Add 2–3 inches of clearance on every side so the unit sits fully on solid concrete.
- Pick a thickness: 3–4 inches for most residential units, 4–6 inches for heavier commercial equipment or unstable soil.
- Enter your dimensions above to get the cubic yardage and bag count.
- Excavate and compact a level base, add a 1–2 inch gravel bed for drainage, then form and pour the slab.
- Keep the pad 3–4 inches above surrounding grade so runoff drains away from the unit.
Worked example
- Pad size
- 30 in × 30 in × 4 in thick
- Volume
- 30/12 × 30/12 × 4/12 = 2.08 ft³, plus 10% waste = 2.29 ft³
- Bags (80 lb, 0.60 ft³ each)
- ceil(2.29 / 0.60) = 4 bags
Common mistakes
- Pouring the pad flush with grade so water pools against the unit — keep it raised 3–4 inches.
- Sizing the pad exactly to the unit’s footprint, leaving no room for service access or minor shifting.
- Skipping the gravel base, which lets the pad settle unevenly over time.
- Using an undersized pad for heavy commercial units, causing cracking under vibration.
Assumptions
- Standard premix concrete at roughly 150 lb per cubic foot.
- Bag yields follow manufacturer averages: 80 lb = 0.60 ft³, 60 lb = 0.45 ft³, 50 lb = 0.375 ft³, 40 lb = 0.30 ft³.
- Waste percentage accounts for spillage, uneven subgrade, and minor overpour.
- Does not include gravel base material, forms, or reinforcement cost.
Frequently asked questions
How thick should a concrete AC pad be?
3 to 4 inches is standard for residential condensers and heat pumps. Larger commercial units, or pads poured over soft or poorly compacted soil, are usually poured 4 to 6 inches thick.
Does an AC pad need rebar or wire mesh?
Most small residential pads (under about 9 square feet) don’t strictly need reinforcement, but a light layer of wire mesh or fiber-reinforced mix reduces cracking, especially in freeze-thaw climates or on units with noticeable vibration.
How much bigger should the pad be than the unit?
Leave at least 2 to 3 inches of clearance beyond the unit’s base on every side. Never pour a pad smaller than the unit’s footprint.