For a typical 10x12 storage shed at 4 inches thick:

• Concrete needed: 1.48 cubic yards (40 cubic feet)
• With 10% waste factor: 1.63 cubic yards (order 1.75 yards)
• Bags required (80-lb): 67 bags (without waste) or 74 bags (with waste)
• Ready-mix cost: $200-$300 (concrete only)
• Total project cost: $400-$800 (including base, labor, materials)

This assumes a 4-inch slab for light storage. Heavier workshops or vehicle storage need 5-6 inches.

Use our concrete calculator for your exact shed dimensions.

1. Basic Volume Formula

Volume (cubic feet) = Length (ft) x Width (ft) x Thickness (ft)

For a 10x12 shed at 4 inches thick:

• Length = 12 feet
• Width = 10 feet
• Thickness = 4 inches = 4 / 12 = 0.333 feet
• Calculation: 12 x 10 x 0.333 = 40 cubic feet

2. Convert to Cubic Yards

You'll order concrete by the cubic yard (1 yard = 27 cubic feet).

Calculation: 40 / 27 = 1.48 cubic yards

Rounded: 1.48 cubic yards (suppliers often round to 1.5 yards)

3. Add Waste Factor

In practice, you'll need extra concrete for:

• Spillage during placement
• Uneven ground
• Formwork adjustments
• Making the slab slightly larger than shed footprint

A good rule of thumb: 10% for small sheds, 15% for irregular shapes.

Calculation with 10% waste: 1.48 x 1.10 = 1.63 cubic yards

Rounded up: 1.63 cubic yards (typically ordered as 1.75 or 2.0 yards).

Note: Bag counts are without waste factor. Add 10% for waste. For 5-inch thick slabs, multiply cubic yards by 1.25.

In practice, shed foundations need special considerations:

• Add 5-10% extra material: Order slightly more concrete than calculated. Leftover material can be used for stepping stones or repairs.
• Thickness depends on use: Light storage = 4 inches. Workshop with heavy tools = 5 inches. Vehicle storage = 6 inches.
• Extend the slab: Make the concrete slab 2-4 inches larger than the shed footprint on all sides for better moisture protection.
• Most people underestimate: Foundation depth, gravel base, and reinforcement all increase material needs.
• Bagged concrete for small sheds: For sheds under 2 yards, bagged concrete is often easier than scheduling a ready-mix truck.

Pro tip: Place anchor bolts in the wet concrete to secure the shed to the slab, preventing wind lift.

Labor cost: Professional installation adds $4-$8 per square foot = $480-$960 for a 10x12 shed.

Total project cost: $400-$800 (DIY) or $820-$1,540 (professional).

How thick should a concrete shed base be?

For most storage sheds, 4 inches is sufficient. For workshops with heavy tools or shelving, go with 5 inches. If storing lawn tractors or vehicles, use 6 inches. Always check your shed manufacturer's recommendations.

Can I use bagged concrete for a shed base?

Yes, bagged concrete works well for shed bases under 2 cubic yards. For a 10x12 shed, you'll need about 67 bags of 80-lb concrete. Mixing that many bags is labor-intensive but avoids truck access issues.

Do I need gravel under a concrete shed base?

Yes, 4-6 inches of compacted gravel is essential for proper drainage and to prevent frost heave. Skip the gravel and your slab may crack within a year.

Should a shed base be bigger than the shed?

Yes, make the concrete slab 2-4 inches larger on all sides than the shed footprint. This prevents water from pooling around the shed walls and provides a slight overhang for runoff.

How long should concrete cure before placing a shed?

Wait 7 days before placing an empty shed, and 28 days before loading it with heavy items. Concrete reaches 70% strength in 7 days and full strength in 28 days.

Do I need rebar or wire mesh in a shed slab?

For sheds under 120 sq ft, wire mesh is optional but recommended. For larger sheds or those in areas with ground movement, use #3 rebar at 24-inch spacing or welded wire mesh.

Ready to Calculate Your Exact Shed Base Needs?

Use our free Concrete Calculator for precise measurements tailored to your specific shed dimensions. Enter any size, thickness, and waste factor for instant cubic yards and bag counts.