How thick should a concrete pad be?

A concrete equipment pad should be at least 4 inches thick for light equipment (AC units, generators). For heavy equipment (forklifts, large HVAC units), use 6 inches. Check the equipment manufacturer specifications for load requirements.

How much does a concrete pad cost?

A concrete pad costs $3–$10 per square foot depending on thickness, location, and whether you hire a contractor. Material alone (ready-mix) costs about $110–$165 per cubic yard. A 10×10 pad at 4 inches uses ~1.23 yards = $143–$203 in material.

Do concrete pads need rebar?

Rebar is recommended for pads supporting heavy equipment or vehicles. Use #4 rebar on 18-inch centers for loads over 500 lbs. For small light-duty pads (AC condenser, small generators), 6×6 welded wire mesh or fiber reinforcement is usually sufficient and easier to work with.

How long before I can place equipment on a new concrete pad?

Concrete reaches approximately 70% of its design strength in 7 days and full strength at 28 days. For light equipment (AC units, small generators), you can typically load the pad after 7 days. For heavy equipment, wait the full 28 days to avoid surface damage or cracking.

What PSI concrete should I use for an equipment pad?

Use 3,000 PSI concrete for standard residential equipment pads. For commercial applications, heavy machinery, or areas with freeze-thaw cycles, specify 3,500–4,000 PSI. In cold climates, ask for air-entrained concrete with 5–7% air content to resist freeze-thaw scaling.

How much bigger should a concrete pad be than the equipment?

The pad should extend at least 2–4 inches beyond the equipment footprint on all sides. This provides stable support for mounting hardware, access for service technicians, and ensures the full weight of the equipment is distributed on concrete rather than soil. For generators and HVAC units, the equipment manufacturer's installation manual often specifies minimum pad dimensions — always check before pouring.

Does a concrete equipment pad need a gravel base?

Yes. A 4-inch compacted gravel base is strongly recommended under any concrete pad. The gravel improves drainage (preventing water from pooling under the slab), provides a stable, compacted surface for the concrete to bear on, and reduces the risk of cracking from differential soil settlement. In areas with expansive clay soils, increase the gravel base to 6 inches and consider adding polypropylene fiber to the concrete mix to control shrinkage cracking.

Concrete Pad Calculator — Cubic Yards, Bags & Cost

What Is a Concrete Equipment Pad?

Use this concrete pad calculator to plan a small, flat concrete slab designed to support mechanical equipment — air conditioning condensers, standby generators, HVAC units, transformers, dumpsters, and similar equipment. Unlike a structural slab or driveway, an equipment pad is engineered primarily for level support and vibration resistance rather than vehicle loads.

Standard residential equipment pads are 4 inches thick for light loads (AC units under 500 lbs) and 6 inches thick for heavier equipment. All equipment pads should be poured on a 4-inch compacted gravel base for drainage, sized 2–4 inches larger than the equipment footprint on all sides, and kept perfectly level — most equipment manufacturers specify a maximum out-of-level tolerance of 1/4 inch. Use 3,000 PSI concrete minimum; 3,500–4,000 PSI in freeze-thaw climates.

How to Use This Concrete Pad Calculator

This concrete pad calculator estimates the volume and bag count for any rectangular pad — equipment pads, utility pads, AC condenser pads, generator bases, and more. Enter the pad length, width, and thickness to get instant results in cubic yards, cubic feet, and number of bags needed. For larger slabs like patios or garage floors, see our concrete slab calculator.

How to Calculate Concrete for a Pad

A concrete pad uses the standard rectangular volume formula: Volume (yd³) = Length (ft) × Width (ft) × Depth (ft) ÷ 27. Always convert thickness from inches to feet by dividing by 12 before calculating.

Example: AC Condenser Pad

A 36 × 36 inch pad at 4 inches thick: length = 3 ft, width = 3 ft, depth = 0.333 ft. Volume = 3 × 3 × 0.333 ÷ 27 = 0.111 cubic yards (about 8 bags of 60 lb concrete).

Example: Generator Pad

A 48 × 72 inch pad at 6 inches thick: length = 4 ft, width = 6 ft, depth = 0.5 ft. Volume = 4 × 6 × 0.5 ÷ 27 = 0.44 cubic yards (about 30 bags of 60 lb concrete).

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Common Concrete Pad Types and Thickness Requirements

AC / HVAC condenser pad — 36×36 inches minimum, 4 inches thick; must be perfectly level and stable to prevent vibration damage to the unit
Standby generator pad — sized to the generator footprint plus 6 inches on each side; 4–6 inches thick depending on generator weight
Dumpster pad — 6 inches thick minimum with rebar reinforcement; must handle repeated heavy loads from garbage trucks
Hot tub / spa pad — 4 inches thick; check the manufacturer's weight specification — a filled spa can weigh 3,000–6,000 lbs or more
Transformer / electrical equipment pad — consult the utility company for size and thickness requirements before pouring

Tips for Pouring a Concrete Equipment Pad

Level is critical — use a laser level or 4-foot level to ensure the finished pad surface is perfectly flat before the concrete sets
Compact the base — add 4 inches of compacted gravel under the pad to prevent settling and improve drainage
Size it right — always extend the pad at least 2–4 inches beyond the equipment footprint on all sides
Add anchor bolts — for equipment that requires bolting down, set anchor bolts or J-bolts in the wet concrete before it cures
Cure before loading — wait at least 7 days before placing heavy equipment on the pad; 28 days for full strength
Budget the full project — use our concrete cost calculator to get a complete material cost estimate including concrete, rebar, and forming supplies

Sources & References

ACI 318-19: Building Code Requirements for Structural Concrete — American Concrete Institute
ASTM C94/C94M: Standard Specification for Ready-Mixed Concrete — ASTM International
PCA: Design and Control of Concrete Mixtures (16th Edition) — Portland Cement Association

Concrete Pad Cost Estimate

Most concrete equipment pads are small enough to pour with bagged concrete, which keeps costs low. An 80 lb bag of premixed concrete costs $5.50–$7.00 and yields about 0.6 cubic feet. For a typical 3×3-foot AC condenser pad at 4 inches thick, you need roughly 8 bags — putting material cost at $45–$55. A larger 4×6-foot generator pad at 6 inches thick requires about 30 bags, costing $165–$210 in concrete alone.

If you hire a contractor, expect to pay $8–$16 per square foot for a finished equipment pad, including excavation, gravel base, forming, concrete, and finishing. A 9-square-foot AC pad runs $75–$150 installed, while a 24-square-foot generator pad costs $200–$400. Add $25–$50 for anchor bolts or J-bolt hardware if your equipment requires tie-downs. For pads over 50 square feet, ordering ready-mix concrete at $130–$165 per cubic yard (plus a possible short-load fee of $50–$100) is usually more economical than hauling dozens of bags.

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Concrete Pad Calculator