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Shed base calculator
Estimate materials for a Australian shed base using sourced concrete, paving slab and plastic grid product examples.
Your result
Your plan starts
with a few details.
Enter the base dimensions from your shed instructions, select a base type and calculate to see an estimated quantity.
How it works
Enter the base footprint from the shed maker’s installation plan. The shed footprint and the required base footprint can differ, so do not assume the shed’s outside dimensions are the correct base size.
Choose concrete, paving slabs or plastic grid. Enter the concrete depth when concrete is selected. For slabs and grids, the estimate uses the cited example unit dimensions and rounds the number of units up. Add an extra percentage only if it suits your cuts and layout, no universal waste allowance is assumed.
You can also enter a road base depth to estimate its in-place volume. The tool does not convert that volume to tonnes or bags because material density, compaction and supplier pack yield vary and are not verified for a named local product here.
Formula
Base area = base length × base width.
Concrete volume = base area × concrete depth in metres. Concrete bags = concrete volume ÷ the cited bag yield, rounded up.
Slab or grid units = base area ÷ the cited unit area, with your extra allowance, rounded up. Sub-base volume = base area × the depth you enter in metres.
Worked example
For a 3 m × 2 m base, area is 3 × 2 = 6 m². At 100 mm concrete depth (0.1 m), volume is 6 × 0.1 = 0.6 m³. The Cement Australia Concrete Mix sheet states a yield of 0.0084375 m³ per 20 kg bag, so 0.6 ÷ 0.0084375 = 72 bags after rounding up.
A 3 m × 2 m grid area using 500 × 500 × 50 mm units needs 24 units by area. This is a count estimate, it does not plan edge cuts or ground preparation.
Assumptions and limits
Concrete bag counts are based on the named Cement Australia Concrete Mix product yield, another mix or bag size can give a different result. The slab and grid counts likewise use one sourced product example each, not a claim that these products are suitable for every shed.
This is a materials takeoff, not structural or ground-condition advice. It does not assess soil bearing capacity, drainage, frost, slope, anchoring, reinforcement, local approvals or the shed manufacturer’s base requirements. Follow the shed instructions and consult a qualified builder or engineer where needed.
Road base output is only the geometric in-place volume at the depth you entered. Compaction, settlement, material density, grading and supplier pack sizes are excluded, so this is not an order tonnage or bag quantity. Confirm the correct preparation and material quantities for your site with a qualified local professional.
Frequently asked questions
Should the base match my shed dimensions?
Use the shed manufacturer’s base plan. The required slab or prepared base may differ from the shed’s outside footprint.
How many concrete bags are needed?
The estimate divides the entered concrete volume by the stated yield for Cement Australia Concrete Mix, then rounds up to whole 20 kg bags. Other products can have different yields.
Does the tool design the base?
No. It estimates quantities only and does not check structural suitability, soil, drainage or approvals. Follow the shed instructions and obtain qualified advice for the site.
Does the sub-base result tell me how many tonnes or bags to order?
No. It shows the in-place MOT Type 1 or road base volume from your entered depth. Density, compaction and supplier bag yield vary, confirm order quantities with your local supplier.
Sources
- Cement Australia Concrete Mix sell sheetChecked on
- Paving products guideChecked on
- EzyHex geo gridsChecked on
Specs as of: