Shed Slab Calculator Australia — Concrete, Bags & Mesh
Slab dimensions
Edge thickening
Results
Concrete volume
Volume breakdown
Bags (if using premix)
Reinforcing mesh
How to calculate concrete for a shed slab in Australia
A standard Australian shed slab uses a flat central panel with a thickened edge beam running around the perimeter. The flat slab volume is length × width × thickness. The edge thickening adds extra concrete along all four sides: perimeter × edge width × (edge depth − slab thickness). Add 10% for wastage, spillage and over-excavation. Mesh quantity is the slab area divided by the sheet size (6 × 2.4 m = 14.4 m²) plus 10% for laps and offcuts. For slabs above about 0.5 m³, a ready-mix truck is more economical than bags.
Shed slab calculator — FAQs
How thick should a shed slab be in Australia?
For a garden shed or small utility shed storing light equipment, 75–100 mm is typically adequate on stable, well-compacted ground. For a garage or workshop with vehicle access, 100–125 mm is standard. Heavy machinery or loaded vehicles require an engineer-designed thickness, typically 125–150 mm or more. AS 2870 and your local NCC requirements will govern the minimum thickness based on soil classification — Class H or reactive soils often require deeper edge beams and heavier reinforcement.
What mesh should I use for a shed slab in Australia?
SL72 (7.6 mm bars at 200 mm centres each way) is the most common residential mesh for shed and garage slabs in Class A and S soil conditions. SL82 or SL92 may be specified for Class M or reactive soils. Trench mesh (TM) is used in the edge beams in many slab designs. Your engineer or certifier will specify the mesh type — do not substitute a lighter mesh without approval as it affects the slab's ability to control cracking in reactive soil conditions.
Do I need a building permit for a shed slab in Australia?
Yes, in most cases. A concrete slab that forms the base of a shed or structure typically requires a building permit, especially if the shed is above a certain floor area (commonly 10 m² in Victoria, 25 m² in Queensland). Even if the shed itself is exempt from a permit in some states, a structural slab poured to support it may require one. Always check with your local council and, in most states, engage a registered building surveyor before starting.
How much does a shed slab cost in Australia?
A basic 6 × 3 m shed slab (18 m²) typically costs $1,500–$3,500 installed, depending on soil conditions, reinforcement requirements and your location. Ready-mix concrete is usually $150–$250 per m³ plus a short-load fee for small pours. Labour, forming, mesh, and base preparation (compacted road base) add the bulk of the cost. Getting 3 quotes from licensed concreters is recommended — prices vary significantly by region and current demand.
How long before I can use a shed slab after pouring?
Concrete reaches approximately 70% of its design strength after 7 days and 95%+ at 28 days (the standard curing period for strength testing). You can typically walk on the slab after 24–48 hours and drive a standard vehicle on it after 7 days in warm conditions. In cold weather (below 10°C) curing slows significantly — extend these times. Keep the slab moist for at least 7 days by covering with plastic sheeting or wet hessian; this dramatically improves surface hardness and reduces cracking.