How Much Concrete for a Shed Foundation: By Size and Foundation Type
A 10×12 shed on a 4-inch concrete slab needs approximately 1.5 cubic yards of concrete (about 40 bags of 80-pound). A 12×16 shed needs roughly 2.4 cubic yards (64 bags). Sonotube footings instead of a full slab drop the concrete volume by 70 to 80 percent. The right answer depends on your shed size, intended use, and local frost depth.
Most shed owners underestimate the foundation. They price out the shed kit, pick a spot, and then realize they have no idea how much concrete for a shed foundation they actually need or whether a full slab is even the right choice. A solid foundation keeps the shed level, dry, and structurally sound for decades. A bad foundation means a warped floor, a door that will not latch, and rot starting within a few years.
This guide gives you the concrete volume for every common shed size in every common foundation type, so you know exactly what to order before you start digging.
Enter your shed dimensions and slab thickness. The calculator gives you cubic yards, bag count, and a cost estimate.
Open the Slab Calculator →Which Shed Foundation Type Is Right for Your Project
Before calculating how much concrete for a shed foundation you need, you need to choose the right foundation type. The three main options are a full concrete slab, concrete sonotube footings with a wood floor frame, and a gravel pad with concrete anchors.
Full concrete slab
A full concrete slab under the entire shed footprint is the most durable and rodent-proof foundation. It is the right choice for workshop sheds, garages, or sheds storing heavy equipment. It requires more concrete but eliminates the wood floor frame and produces a level, washable surface. Standard thickness is 4 inches for light storage; 5 to 6 inches for heavy equipment or vehicle storage. How much concrete for a shed foundation this size depends directly on the footprint and thickness.
Sonotube footings with wood frame floor
Four to six concrete sonotube footings at the perimeter corners and midpoints, with a pressure-treated wood frame and plywood floor above. This method uses far less concrete (one to two bags per footing vs 40 to 60 bags for a full slab), but requires the floor frame to be set at the right height and level. It is appropriate for garden storage sheds, small workshops, and sheds in areas where a full slab would require significant excavation or grading. For the sonotube bag count, our guide on how much concrete for sonotube footings gives you the exact figures by diameter and depth.
Gravel pad with concrete anchors
A compacted gravel pad is a fast, low-cost base for smaller prefab sheds. Adding concrete anchor blocks at the corners gives the shed tie-down resistance against wind. This method uses minimal concrete (4 to 6 bags for corner blocks) and is appropriate for 8×10 or smaller sheds in non-frost-prone climates. It is not appropriate for any application where the floor will carry heavy loads.
How Much Concrete for a Shed Foundation by Shed Size
The figures below answer how much concrete for a shed foundation at standard 4-inch slab thickness. For other thicknesses, the cubic yard figure scales linearly with thickness.
| Shed size | Sq footage | Cubic yards | 80-lb bags | Ready-mix viable |
|---|---|---|---|---|
| 6×8 | 48 sq ft | 0.6 cu yd | 16 bags | No (short-load fees) |
| 8×10 | 80 sq ft | 1.0 cu yd | 27 bags | Borderline |
| 10×12 | 120 sq ft | 1.5 cu yd | 40 bags | Yes (1 min order) |
| 12×16 | 192 sq ft | 2.4 cu yd | 64 bags | Yes |
| 12×20 | 240 sq ft | 3.0 cu yd | 80 bags | Yes |
| 16×20 | 320 sq ft | 4.0 cu yd | 107 bags | Yes |
| 20×24 | 480 sq ft | 6.0 cu yd | 160 bags | Yes |
| 24×24 | 576 sq ft | 7.1 cu yd | 191 bags | Yes |
For context on the broader cost of a concrete slab project, our concrete slab cost guide covers installed pricing from contractors. If you are trying to minimize how much concrete for a shed foundation by using sonotube footings instead, keep in mind that sonotube installations still require accurate concrete volume estimates. And for a reference on the math approach for volume of any rectangular slab, our guide on how much concrete for a 24×24 slab walks through the same formula in detail.
Concrete Volume at Different Slab Thicknesses
| Slab thickness | Cubic yards | 80-lb bags | When to use |
|---|---|---|---|
| 3.5 inches (minimum) | 2.1 cu yd | 56 bags | Light garden storage only |
| 4 inches (standard) | 2.4 cu yd | 64 bags | Standard garden and tool shed |
| 5 inches | 3.0 cu yd | 80 bags | Light equipment, riding mower |
| 6 inches | 3.6 cu yd | 96 bags | Heavy equipment, vehicle storage |
Sonotube Footing Option: Much Less Concrete
If you choose sonotube footings instead of a full slab for a 12×16 shed, you need 6 footings (4 corners plus 2 midpoints on the long sides). At a standard 10-inch tube at 36-inch depth, each footing takes 2.7 bags (round to 3). Six footings: 18 bags total. That is 1/3 the concrete of the full slab option, at the cost of needing a wood floor frame above the footings. For the complete bag count by tube diameter and depth, our sonotube concrete guide has every combination you need.
Three Real Shed Foundation Projects
Example 1: 10×12 workshop shed in Kansas City, Missouri
A homeowner wanted a 10×12 workshop shed with a concrete floor that could handle a heavy workbench and tool storage. Full slab, 4-inch thickness: 1.5 cubic yards = 40 bags with 10% waste. Kansas City gets freeze-thaw cycles, so 4,000 PSI air-entrained mix was specified. The homeowner ordered one cubic yard of ready-mix from a local batch plant (just at the minimum threshold) and supplemented with 14 bags of bagged 4,000 PSI concrete for the edges. Total concrete cost: $180 ready-mix + $112 bags = $292. The gravel base prep cost more than the concrete.
Example 2: 12×20 storage shed in Tampa, Florida
A 12×20 garden shed for lawn equipment and bicycles in Tampa. Tampa’s frost depth is zero, so 3,000 PSI concrete is adequate. Full slab: 3.0 cubic yards. Ready-mix from a local plant at $130 per yard: $390. Delivery: $85. Total concrete cost: $475. The shed itself cost $2,800 assembled. The concrete foundation was 17 percent of the total project cost but will outlast several shed structures built on top of it.
Example 3: 8×10 backyard shed with sonotube footings in Denver, Colorado
A homeowner in Denver wanted an 8×10 shed for seasonal storage. Denver frost depth is 36 inches, making a full slab pour with proper edge thickening complex. The homeowner chose 4 sonotube footings at 8-inch diameter x 42-inch depth. Bags per footing: 1.4 bags (round to 2). Four footings: 8 bags. A pressure-treated 2×8 frame with 3/4-inch plywood floor went on top. Total concrete: 8 bags at $10 each = $80. The wood frame floor cost $220. Total foundation: $300 versus $400 to $600 for a full mini-slab at this size. Correct answer for the climate and scale.
Enter your shed dimensions and get your cubic yard count for any thickness. Know exactly what to order before calling the ready-mix plant.
Calculate Shed Slab Volume →Frequently Asked Questions About Concrete for a Shed Foundation
How much concrete do I need for a shed foundation?
A 10×12 shed on a 4-inch concrete slab needs approximately 1.5 cubic yards (40 bags of 80-pound concrete). A 12×16 shed needs 2.4 cubic yards (64 bags). For sonotube footings instead of a full slab, a 4-footing configuration for a small shed uses 8 to 18 bags total depending on tube diameter and frost depth.
Do I need a concrete slab for a shed?
No. A concrete slab is the most durable shed foundation but is not always necessary. Concrete sonotube footings with a wood frame floor are appropriate for most garden and storage sheds. A compacted gravel pad works for small prefab sheds in frost-free climates. A full slab is the right choice when you need a washable floor, heavy equipment access, or rodent proofing.
How thick should a concrete shed slab be?
Four inches is the minimum for a standard shed. Light garden storage sheds can use 3.5 inches but this is the bottom of the acceptable range. Sheds storing riding mowers, ATVs, or heavy shop equipment should use 5 inches. Vehicle storage applications need 5 to 6 inches. Each additional inch adds roughly 25 percent to the concrete volume.
How many bags of concrete for an 8×10 shed slab?
An 8×10 shed on a 4-inch slab requires approximately 1.0 cubic yard of concrete. At 0.60 cubic feet per 80-pound bag, that is about 27 bags with a 10 percent waste factor included. At this volume, you are at the borderline between bagged concrete and a ready-mix order, depending on your local supplier’s minimum and short-load fees.
Do I need rebar in a shed slab?
Wire mesh is standard for most shed slabs under light to moderate loads. Rebar is the upgrade for sheds that will store heavy equipment, vehicles, or anything that concentrates load on a small area. For a garden storage shed, wire mesh is adequate and saves $1 to $2 per square foot over rebar. For a vehicle or heavy equipment shed, rebar is worth the additional cost.
Does a shed slab need a gravel base?
Yes. A 4-inch compacted gravel base under the concrete slab provides drainage and prevents heaving in freeze-thaw climates. Without a gravel base, water trapped under the slab expands when it freezes and cracks the concrete from below. In warm, well-drained soils, 4 inches of compacted gravel is standard. In cold climates or clay soils, 6 to 8 inches of gravel provides better protection.
Can I pour a shed slab myself?
Yes, for slabs under about 2 cubic yards. Beyond that, the timing pressure of working with setting concrete makes it difficult for a solo or two-person crew. A 10×12 slab (1.5 cubic yards) is at the upper practical limit for a competent DIYer working with a helper. A 12×16 or larger slab is more manageable with a ready-mix truck and three or more people to screed, float, and finish before the concrete sets.
What concrete PSI should I use for a shed slab?
3,000 PSI is the minimum for a shed slab in warm climates without freeze-thaw cycling. In any climate that sees below-freezing temperatures, 4,000 PSI air-entrained concrete is the correct specification. Air entrainment creates microscopic bubbles that accommodate ice crystal expansion and prevent surface scaling after freeze-thaw cycles.
Related Calculators and Guides
For shed foundation requirements by local code, the International Residential Code (IRC) Section R105.2 covers permit exemptions for accessory structures, which may include your shed depending on size and location relative to property lines.