Concrete Shed & Equipment Pad Calculator

Enter your pad's length, width, and thickness to instantly calculate concrete volume in cubic yards, number of bags needed, and total cost estimate — for shed slabs, generator pads, AC unit bases, and any small equipment foundation.

Free to use No sign-up required Industry-standard formula Imperial & metric supported

✓ Bag count (60 lb & 80 lb) ✓ Cost estimator included ✓ Works for any pad type ✓ Last verified May 2026

Reviewed by the AllConcreteCalculator.com editorial team — formulas cross-checked against ACI 318 standards, May 2026.

Enter Your Pad Dimensions

Pad Length

Measure the longest outside dimension of the pad. Please enter a valid length greater than 0.

Pad Width

The shorter outside dimension of the pad. Please enter a valid width greater than 0.

Pad Thickness

Shed slab: 4 in. Equipment/generator pad: 6 in. Heavy HVAC or industrial: 6–8 in.

Please enter a valid thickness greater than 0.

Waste / Overage Factor (%)

10% is standard for small pads. Use 5% if mixing bagged concrete yourself — waste is easier to control.

Price per Cubic Yard (optional)

Leave blank to skip cost estimate. US average: $100–$150/yd³ for ready-mix. Small pads often use bagged concrete.

Results appear instantly. No sign-up required.

Your Pad Concrete Estimate

Concrete Volume (with waste)

—

Cubic Yards (yd³)

—

Cubic Feet (ft³)

—

Cubic Meters (m³)

Bags Required (includes waste)

—

40 lb bags

—

60 lb bags

—

80 lb bags

— Area (sq ft)

— Area (m²)

— Thickness

— Waste Factor

Estimated Material Cost

—

Concrete material cost only. Add forming lumber ($20–$60 for a small pad), gravel base, and any anchor bolt hardware. Use our Full Project Estimator for a complete budget breakdown.

Step 1: Convert all dimensions to feet
Step 2: Volume (ft³) = Length (ft) × Width (ft) × Thickness (ft)
Step 3: Cubic Yards = ft³ ÷ 27
Step 4: Final Volume = Volume × (1 + waste% ÷ 100)
Step 5: Bags = CEIL(Final ft³ ÷ bag yield) — always round up, never down

Bag yields: 40 lb = 0.30 ft³ | 60 lb = 0.45 ft³ | 80 lb = 0.60 ft³

How to Use This Shed & Equipment Pad Calculator

Measure the outside footprint of your pad. Use a tape measure to get the length and width of the area you plan to pour — measuring the inside dimensions of the form you'll build, not the outside edge of the lumber. For a shed, measure the actual shed base footprint and add at least 2 inches per side for overhang. Record dimensions in whatever unit is easiest; the calculator handles the conversion automatically.
Select the correct thickness for your application. Use the quick-select buttons — [4 in], [6 in], [8 in] — or type your own value. For a basic storage shed, 4 inches is the minimum. For a generator, AC condenser, or HVAC unit, use 6 inches. For heavy industrial equipment or anything with anchor bolts carrying significant load, use 6–8 inches with rebar or fiber reinforcement.
Set your waste factor and optional price. The default 10% is appropriate for a standard rectangular pad. If you're confident in your formwork and ordering from a reliable ready-mix supplier, 7–8% is acceptable for experienced pours. Enter a price per cubic yard to see a material-only cost estimate. Leave it blank to skip cost output.
Use the results to order or buy materials. The cubic yards figure is what you tell a ready-mix dispatcher. The bag counts tell you how many bags to pick up at the hardware store. Most small equipment pads under 1 cubic yard are best done with bagged concrete — it's practical and avoids short-load fees from ready-mix plants.

⚠ Pro Tip: The most common mistake on small equipment pads is forgetting to extend the slab beyond the equipment footprint. Air conditioners, generators, and compressors vibrate — the pad should extend at least 6 inches past the equipment on every side to provide a stable bearing zone and prevent edge cracking under load.

Concrete Pad Volume Formula

The calculation uses the standard rectangular volume formula — the same math your ready-mix supplier uses when you call in an order. Pad orientation doesn't matter: entering 10 ft × 8 ft or 8 ft × 10 ft produces the same result.

Step	Formula	Example (10 × 8 ft, 4 in)
1. Convert thickness to feet	inches ÷ 12	4 ÷ 12 = 0.333 ft
2. Volume in cubic feet	L × W × T	10 × 8 × 0.333 = 26.67 ft³
3. Convert to cubic yards	ft³ ÷ 27	26.67 ÷ 27 = 0.988 yd³
4. Add waste factor (10%)	Volume × 1.10	0.988 × 1.10 = 1.086 yd³
5. Bag count (80 lb bags)	CEIL(ft³ ÷ 0.60)	CEIL(29.33 ÷ 0.60) = 49 bags

Common Shed & Equipment Pad Reference Table

Concrete volumes and bag counts — no waste factor applied. Add 10% for real-world ordering.
Pad Size	Thickness	Cubic Yards	60 lb Bags	80 lb Bags	Typical Use
4 × 4 ft	4 in	0.20 yd³	15 bags	11 bags	AC condenser (small)
4 × 6 ft	4 in	0.30 yd³	22 bags	16 bags	Generator or AC unit
6 × 6 ft	4 in	0.44 yd³	33 bags	25 bags	Small utility shed
8 × 8 ft	4 in	0.79 yd³	59 bags	44 bags	Small shed slab
10 × 10 ft	4 in	1.23 yd³	92 bags	69 bags	Standard 10×10 shed
10 × 12 ft	4 in	1.48 yd³	110 bags	82 bags	Standard 10×12 shed
12 × 16 ft	4 in	2.37 yd³	176 bags	132 bags	Large storage shed
4 × 6 ft	6 in	0.44 yd³	33 bags	25 bags	Generator (heavy)
6 × 8 ft	6 in	0.89 yd³	66 bags	49 bags	HVAC equipment pad
10 × 10 ft	6 in	1.85 yd³	137 bags	103 bags	Workshop shed, 6 in thick
3 × 3 ft	8 in	0.22 yd³	17 bags	12 bags	Large standby generator
4 × 8 ft	8 in	0.79 yd³	59 bags	44 bags	Industrial compressor pad

Bag counts assume no waste factor. Add 10% for real-world ordering. Values rounded up to nearest whole bag.

What Thickness Does Your Concrete Pad Need?

Pad thickness is determined by what's sitting on it — the type and weight of the equipment, whether it vibrates, and whether anchor bolts are required. Getting this wrong in either direction is costly: too thin and you'll see cracking and settlement; too thick and you've wasted money on concrete you didn't need.

Recommended concrete pad thickness by equipment type and application.
Application	Recommended Thickness	Min. PSI	Reinforcement	Notes
Storage shed (no vehicle access)	4 inches	3,000 PSI	Optional wire mesh	Standard for small sheds under 200 sq ft
Workshop / hobby shed	4–6 inches	3,000 PSI	Wire mesh recommended	Use 6 in if storing heavy equipment inside
AC condenser / heat pump	4 inches	3,000 PSI	None required	Pad must extend 3–6 in beyond unit on all sides
Residential generator (portable)	4 inches	3,000 PSI	None required	Anchor to pad if in high-wind zone
Standby / stationary generator	6 inches	3,500 PSI	Rebar or fiber	Anchor bolts embedded at pour; use template
HVAC / commercial equipment	6 inches	3,500 PSI	Rebar required	Vibration from compressors demands rebar
Pool pump / filter equipment	4 inches	3,000 PSI	None required	Seal surface to resist chemical spills
Industrial compressor / machinery	6–8 inches	4,000 PSI	Rebar, engineer spec	Isolate pad from building slab (expansion joint)

If your generator or equipment pad requires anchor bolts, cut a bolt template from scrap plywood before pouring. Set the template in the wet concrete to hold bolt positions precisely while the pad cures. Repositioning anchor bolts after cure is an expensive mistake that requires cutting, patching, or epoxy anchors.

Common Mistakes When Estimating Shed & Equipment Pads

📐
Sizing the pad to match only the equipment footprint. The pad must extend beyond the equipment on all sides — typically 4–6 inches for AC condensers and generators, and up to 12 inches for vibrating industrial equipment. A pad that barely fits the unit has no tolerance for anchor bolt misalignment and will crack at the edges under operational vibration.
⚓
Setting anchor bolts without a template. For standby generators and mounted equipment, anchor bolt spacing is specified by the manufacturer to the fraction of an inch. Placing bolts by eye or measuring from the edge of a form while the concrete is setting is almost guaranteed to be off. Always fabricate or purchase a bolt template and set it in the wet concrete immediately after screeding.
🪨
Skipping gravel base preparation. Even for a small shed or AC pad, pouring directly on unprepared soil leads to differential settling — one corner of the pad sinks while the others don't, causing the equipment to become unlevel and the pad to crack. Always excavate 4 inches, compact the subgrade, and add a compacted gravel base before forming.
📦
Underestimating how many bags to buy for a small pad. Most small equipment pads are under 1 cubic yard and done with bagged concrete. People consistently underestimate the count because they calculate at 100% efficiency — no spills, no mixing losses, no waste. Always add at least 10% to your calculated bag count and buy that number in one trip. Running back to the hardware store mid-pour while concrete sets in your mixer or wheelbarrow is a job-killer.
🏗️
Not isolating the equipment pad from adjacent slabs. If your generator or HVAC pad is poured adjacent to a house foundation, garage floor, or existing slab, you must install a foam isolation joint between them. Equipment vibration will crack the adjacent structure if the two slabs are bonded together — the pads must be free to move independently.

Frequently Asked Questions

For a standard storage shed, 4 inches is the industry-standard minimum. This is sufficient for foot traffic, stored tools, and light equipment like lawn mowers and bikes. If you plan to store heavier items — a riding mower, ATV, small tractor, or workshop machinery — use 6 inches and add wire mesh or fiber reinforcement. In freeze-thaw climates, a thicker slab with proper drainage under it will resist heaving far better than the minimum 4 inches.
A 4-inch concrete pad is sufficient for a residential air conditioner or heat pump condensing unit. The load from a residential AC unit is relatively light — typically 150–300 lbs — and doesn't require the depth needed for vibrating industrial equipment. The more important consideration is the pad size: it must extend 3–6 inches beyond the unit footprint on all sides, and the surface should be level to within 1/4 inch to prevent refrigerant oil pooling issues and warranty voiding. Concrete pre-made pads (sometimes called "patio blocks") are also an acceptable alternative for small residential AC units.
A 10 × 12 ft shed slab at 4 inches thick requires 40 cubic feet of concrete without waste, which equals 1.48 cubic yards. With a 10% waste factor, you need 1.63 cubic yards. In bags: approximately 91 bags of 60 lb (0.45 ft³ each) or 74 bags of 80 lb (0.60 ft³ each), rounded up. At 74 bags of 80 lb concrete, you're at the upper practical limit for bagged concrete — mixing that volume by hand is exhausting and slow. Many contractors recommend calling a ready-mix supplier for anything over 1 cubic yard; a short load fee is typically less than the labor and time saved.
Size the pad to match the generator's base frame dimensions plus at least 6 inches of overhang on each side. For a typical 7,500–12,000-watt portable generator, a 4 × 6 ft pad at 4 inches thick is adequate. For a whole-house standby generator (air-cooled, 10–20 kW), a 3 × 5 ft to 4 × 6 ft pad at 6 inches thick is standard, with anchor bolts embedded at manufacturer-specified locations. For larger liquid-cooled standby units, always check the generator manufacturer's installation manual for specific pad dimensions and anchor bolt template requirements.
Rebar is not strictly required for a basic storage shed slab or light residential equipment pad in stable soil conditions. However, wire mesh (welded wire fabric) or fiber reinforcement (polypropylene fibers added to the mix) is strongly recommended for any pad over 6 × 6 ft or in areas with expansive clay soils or freeze-thaw cycles. Rebar (#3 or #4 bar on 12-inch centers) is required for generator pads with anchor bolts under tensile load, any pad carrying vibrating equipment, and any pad adjacent to a vehicle traffic area. The cost of adding fiber to the mix ($5–$15/yard) is trivial insurance against cracking.
For pads under 0.75 cubic yards (about 20 cubic feet), bagged concrete mixed in a rented drum mixer or large trough is entirely practical for a capable homeowner. Above 1 cubic yard, the labor of mixing bags becomes significant — a 10 × 12 shed slab at 4 inches is about 1.5 cubic yards, which means hand-mixing 90+ bags. At that volume, calling a ready-mix supplier is worth the short-load fee (typically $50–$150 on top of the per-yard price for loads under 5 yards). The pour will also be faster, more consistent, and less physically demanding.
Light items can be placed on a pad after 24–48 hours, once it can support foot traffic without surface damage. However, for equipment pads, wait a minimum of 7 days before placing any load and 28 days before putting the equipment into operation — especially for vibrating equipment like generators and compressors. The concrete reaches approximately 70% of its design strength at 7 days and full design strength at 28 days. Placing a vibrating generator on a 3-day-old pad risks cracking and surface degradation, potentially voiding the concrete's structural integrity.
Yes, in almost all cases. Excavate the top 4–6 inches of topsoil and organic material, compact the native subgrade with a plate compactor, then add a 4-inch layer of compacted crushed stone or road base. This provides drainage under the slab (preventing moisture from wicking up) and a uniform bearing surface that won't compact further under load. Pouring directly on unprepared soil — especially in areas with clay or organic matter — leads to differential settlement and cracking within the first few years. The gravel base is not optional in freeze-thaw climates; without it, heave from ground frost will crack even a properly reinforced slab.
Permit requirements vary by municipality. In most US jurisdictions, a concrete pad for an accessory structure like a shed does not require a permit if the shed itself is under the exempt square footage threshold (commonly 120–200 sq ft). However, the shed may require a permit even if the slab doesn't. Equipment pads for standby generators often require an electrical permit for the transfer switch and generator hookup, even if the concrete pad itself doesn't require a building permit. Always check with your local building department before starting — and if your neighborhood has an HOA, get written approval for placement and appearance of the structure and its foundation before breaking ground.
For a basic storage shed slab, 3,000 PSI ready-mix is the industry minimum. For equipment pads, generator pads, and HVAC equipment foundations, specify 3,500 PSI. In freeze-thaw climates, use 4,000 PSI with 5–7% air entrainment regardless of application — the entrained air bubbles give the concrete room to expand during freeze cycles without surface scaling. Bagged concrete (Quikrete, Sakrete, etc.) typically meets or exceeds 4,000 PSI when mixed to the manufacturer's water ratio — don't add extra water to make it easier to work with, as it significantly reduces final strength.