Concrete Equipment Pad Calculator

How it's calculated

The calculator finds the volume in cubic feet: length (ft) × width (ft) × thickness (in ÷ 12). That's converted to cubic yards by dividing by 27. A waste percentage is added on top to cover over-excavation and form loss, and the adjusted cubic yardage is multiplied by concrete's density to get the weight in tons. Bag counts divide the adjusted cubic feet by each bag's yield; ready-mix truckloads divide the adjusted cubic yards by the truck's capacity — for a pad this size, bags are often the practical choice.

Worked example

A 3 ft × 5 ft generator pad poured 6 inches thick: volume = 3 × 5 × (6 ÷ 12) = 7.5 cubic feet. In cubic yards, that's 7.5 ÷ 27 = 0.28 yd³. Adding a 10% waste factor: 0.28 × 1.10 = 0.31 yd³. At 2.02 tons per cubic yard, that's 0.31 × 2.02 = 0.62 tons — or 0.60–0.62 tons across the 1.95–2.03 density range. In 60 lb bags, the adjusted 8.25 cu ft (7.5 × 1.10) needs 19 bags — well within reach of a bagged pour for a pad this size.

How deep should it be?

An equipment pad often needs to be thicker relative to its footprint than a patio or walkway slab of similar size, and the reason is what's sitting on it rather than the pad's own dimensions: equipment feet, vibration isolators, and mounting rails concentrate load onto a few small contact points instead of spreading it evenly the way foot traffic does, and rotating or reciprocating machinery — a compressor, a generator's engine — adds vibration that a thin, lightly reinforced slab can crack or shift under over time. Anchor bolts add their own requirement: many units need bolts or brackets embedded to a specific depth, set at the manufacturer's exact bolt pattern before the pour, not drilled in as an afterthought — and embedment depth alone can call for more thickness than a purely decorative slab would ever need. Drainage matters differently here too: a pad should sit slightly above the surrounding grade, not flush with it or below, so water sheds away from the unit's base rather than pooling against equipment that often has electrical connections close to the ground — a patio only needs to slope water away from a house, but a pad needs to keep water off the equipment sitting directly on it. None of this — thickness, anchor bolt pattern and embedment depth, pad footprint, or required clearances — is a number this calculator supplies or should: the equipment manufacturer's own installation manual publishes exact pad requirements for that specific unit, and your local building or electrical code governs setbacks and clearances on top of that, sometimes with additional rules for a generator's noise or fuel storage. This calculator converts the length, width, and thickness you already have from those sources into a volume and weight — it doesn't set the dimensions for you.

Common mistakes

• –Assuming a patio or walkway's thickness is enough for equipment. Point loads, anchor bolt embedment, and vibration from rotating machinery all call for more mass than foot traffic ever does — check the manufacturer's pad spec rather than reusing a patio number.
• –Forgetting anchor bolts or brackets until after the pour. Most equipment needs bolts embedded at a specific pattern and depth set before or during the pour, not drilled in afterward — check the manufacturer's installation manual for the exact layout before you form the pad.
• –Pouring the pad flush with or below surrounding grade. Water pooling against equipment with electrical connections near the ground is a real failure mode, not a cosmetic issue — the pad should sit slightly above grade so water sheds away from the unit.
• –Sizing the pad by eye instead of the manufacturer's spec sheet. HVAC, generator, and compressor manufacturers publish exact pad dimensions, thickness, and anchor patterns for their specific units — a pad that's the wrong size can complicate a warranty claim or fail an inspection.
• –Ignoring vibration when planning the mix or reinforcement. Rotating or reciprocating equipment transmits real vibration into the pad over years, part of why equipment pads often call for a different reinforcement or thickness spec than a static patio slab the same size.

Where the density figure comes from

Unlike the landscape materials on this site, concrete is a manufactured product with a tightly controlled mix, so its density varies far less than gravel, sand, or mulch — and the same figure applies whether it's poured as a slab, an equipment pad, or any other normal-weight element. CEMEX, a major ready-mix producer, puts a solid unbroken pour at about two tons (4,000 lbs) per cubic yard. ACI 318 and ASTM C138 define normal-weight concrete at 145–150 lb/ft³ — ACI 318 uses 150 lb/ft³ as its default structural value — which works out to 3,915–4,050 lbs (1.96–2.03 tons) per cubic yard. The 1.95–2.03 ton/yd³ range here reflects that normal-weight span, not moisture variation. Lightweight and heavyweight concrete mixes fall outside this range and aren't covered by this calculator. We use 2.02 tons/yd³ as the display figure, drawn from:

• CEMEX — Ready-Mix Concrete Calculator
• ACI 318 & ASTM C138 — normal-weight concrete density, 145–150 lb/ft³

Read more in our density methodology.

FAQ

How thick should an equipment pad be?

It depends on the specific unit — its weight, vibration, and anchor bolt requirements — which the manufacturer's own installation manual publishes for that model. Your local building or electrical code may add clearance or setback requirements on top of that. This calculator only converts whatever thickness you enter into a volume and weight.

Why are equipment pads thicker than a patio of the same size?

Equipment concentrates load onto a few small contact points instead of spreading it out the way foot traffic does, and rotating or reciprocating machinery adds vibration a thin slab can crack or shift under over time. Anchor bolt embedment depth can also call for more thickness than a purely decorative slab needs.

Do I need anchor bolts in the pad?

Most HVAC, generator, and compressor units do. Bolts or brackets are typically set at a specific pattern and depth before or during the pour, per the manufacturer's installation template — check that document before you form the pad, since retrofitting anchors after the pour is far more difficult.

Should the pad sit above grade?

Generally yes. A pad poured flush with or below the surrounding grade lets water pool against the equipment's base, which is a real problem for units with electrical connections close to the ground. A slight rise above grade sheds water away from the equipment instead.

Where do I find the right pad size for my HVAC unit or generator?

The manufacturer's installation manual or spec sheet for that specific model — pad dimensions, thickness, and anchor bolt pattern are usually published there. Your local code may add clearance, setback, or (for a generator) noise and fuel-storage requirements on top of the manufacturer's own spec.

Should I use bags or ready-mix for an equipment pad?

Bags are often the practical choice — most equipment pads are small enough to stay well within reach of a bagged DIY pour. Past roughly half a cubic yard, which a larger generator or shed pad can reach, ready-mix delivery is usually cheaper and far less labor than mixing dozens of bags by hand.

Why does concrete's weight vary so little compared to gravel or sand?

Concrete is a manufactured product with a tightly controlled mix ratio, so its density is far more consistent than a quarried or organic material's. The range on this site comes from ACI 318 and ASTM C138's normal-weight concrete specification (145–150 lb/ft³), the same figures used across every concrete calculator here, not from moisture swings the way gravel, sand, or mulch vary.