Material list estimate: lumber, siding, and roofing
This shed calculator sizes the big three material groups for a backyard shed: the concrete slab, the lumber frame, and the roof. Enter footprint dimensions and the tool computes concrete volumes, stud counts, and sheeting areas locally in your browser.
Shed math rewards precision because materials come in fixed units — bags of concrete, 8-foot studs, 4×8 sheets of plywood — and ordering correctly avoids both mid-job store runs and a garage full of leftovers.
Slab volume is length × width × thickness. Since one cubic yard is 27 cubic feet, a 10×12 slab at 4 inches thick is 10 × 12 × (4/12) = 40 cubic feet = 1.48 cubic yards — too big for bags, so order ready-mix by the yard. A bag-friendly 8×10 slab at 4 inches is 26.7 cubic feet, which is 45 eighty-pound bags (each yields 0.60 cubic feet) or 60 sixty-pound bags (0.45 cubic feet each).
Thickness choices: 4 inches suits typical storage sheds on stable soil; go 5 to 6 inches with #3 or #4 rebar or wire mesh if you store a riding mower or tractor. Always include a compacted gravel base of 4 to 6 inches under the slab, and slope the surface about 1/8 inch per foot if you'll hose it out.
The computed values below cover three common shed footprints at a 4-inch thickness, shown in cubic feet, cubic yards, and both bag sizes. Read bags as whole numbers rounded up — concrete does not keep.
For example, the 12×16 slab needs 2.37 cubic yards; a typical ready-mix truck carries 8 to 10 yards, so it may be cheaper to order this with a neighbor's pour or use a trailer-mounted mixer.
| Slab (ft, 4 in thick) | Cubic feet | Cubic yards | 80-lb bags | 60-lb bags |
|---|---|---|---|---|
| 8 × 10 | 26.7 | 0.99 | 45 | 60 |
| 10 × 12 | 40.0 | 1.48 | 67 | 89 |
| 12 × 16 | 64.0 | 2.37 | 107 | 143 |
Walls: for 8-foot walls with studs 16 inches on center, count studs per wall as length ÷ (16/12) + 1, then double up end and corner studs and add plates — three 2×4s run the full wall length for top double plate and bottom plate. An 8×10 shed's two 10-foot walls take 8 studs each and its two 8-foot walls take 7 each, roughly 30 studs plus 15 for doubled members and door framing.
Roof: a simple gable over an 8×10 shed with a 12-inch overhang needs rafters spaced 24 inches on center — 6 pairs along the 10-foot run — each cut to sqrt(half-span² + rise²) plus overhang. Sheath walls and roof with 4×8 plywood: wall area plus roof area (footprint × pitch multiplier plus overhangs) divided by 32 square feet per sheet, plus 10 percent waste.
Not every shed needs a slab. A gravel pad of crushed stone at 4 to 6 inches depth, contained by a treated lumber perimeter, suits smaller sheds and drains well — gravel volume works the same as concrete: area × depth ÷ 27 for cubic yards.
Skid foundations (treated 4×4 or 6×6 runners) and concrete pier blocks cut cost further and simplify permits in many jurisdictions, since a movable structure often escapes the permit process. Match the foundation to the use: slabs for heavy equipment, piers for light storage, gravel for everything in between.
['Anchoring turns a shed from a box into a lasting structure: on a slab, use anchor bolts set in wet concrete every 4 to 6 feet along the sill; on skids, tie down with ground anchors rated for your wind zone. Floor systems over piers or skids use treated rim joists and joists at 16 inches on center for 5/8-inch plywood decking, or 24 inches for 3/4-inch.', 'Compute joists the same way as wall studs: joist count ≈ length ÷ (16/12) + 1. An 8×10 floor takes 9 joists (2×6 treated spans 10 feet adequately at 16 inches on center for light storage), plus rim boards on the perimeter. Multiply by 1.1 for cutting waste on all lumber orders.', 'Finishing touches protect the investment: prime and paint all exterior cuts, install drip cap over openings, and keep siding at least 6 inches off grade to prevent rot. Inside, a single pitched-roof vent and a small gable vent reduce summer heat and moisture — cheap insurance for whatever you store.']
How many bags of concrete do I need for a 10x12 shed slab?
A 10×12 slab at 4 inches is 40 cubic feet = 1.48 cubic yards. That equals 67 eighty-pound bags or 89 sixty-pound bags — at that scale, ready-mix delivered by the yard is usually cheaper and far less labor.
How thick should a shed slab be?
Four inches is standard for storage sheds on well-drained soil. Use 5 to 6 inches with reinforcement (rebar or wire mesh) if the shed will hold a tractor or vehicle, and pour on 4 to 6 inches of compacted gravel.
How much gravel do I need under a shed?
Gravel volume equals area × depth ÷ 27 in cubic yards. A 10×12 base at 4 inches needs 480 ÷ 12 × (4/12) = 40 cubic feet ≈ 1.5 cubic yards — convenient, since it matches the concrete volume above it.
How many studs do I need for a shed wall?
At 16 inches on center, studs per wall ≈ wall length in feet × 0.75 + 1, plus doubled corners and door framing. An 8×10 shed with one door typically totals around 45 to 50 studs for all four walls.
Do I need a permit for a shed?
Rules vary by jurisdiction, but common thresholds trigger permits at 120 square feet (the IBC's definition separating sheds from accessory buildings), and many areas exempt smaller, non-permanent foundations. Check with your local building department before pouring anything.