Foundation Calculator
Estimate the concrete volume required for strip or pad foundations beneath a structure, extension or outbuilding.
Foundation Calculator
Estimate concrete volume for pad and strip foundations beneath a structure.
Estimating Foundation Concrete
Foundations transfer the load of a structure down to bearing ground, and their design generally falls into one of two categories: a continuous strip footing running under load-bearing walls, or a series of isolated pad footings supporting individual posts or columns. This calculator handles both, using straightforward volume maths so you can estimate concrete quantities before finalising engineering drawings.
For a strip footing, the calculation is total length (m) × width (m) × depth (m), using your entered width and depth in millimetres converted to metres. For pad footings, each pad's volume is calculated the same way and then multiplied by the number of pads. In both cases, a recommended order volume adds 5 per cent to allow for minor formwork variation and site conditions, and approximate weight is calculated using a standard concrete density of 2.4 tonnes per cubic metre.
What Information You Need To Enter
Choose whether you are estimating a strip or pad footing. For a strip footing, enter the total footing length in metres along with width and depth in millimetres. For pad footings, enter each pad's length and width in millimetres, the depth in millimetres, and how many pads are needed.
Understanding Your Results
You will see the concrete volume required, a recommended order volume with a 5 per cent allowance, and the approximate weight in tonnes. These figures help you plan concrete delivery and compare footing options, though your final footing size and depth should always be confirmed by a structural engineer based on soil conditions and the loads involved.
Why Accurate Estimating Matters
Getting foundation quantities right before you order concrete avoids an under-supply that stalls the pour partway through, or an over-order that wastes money. It also gives you a clearer budget figure while you are still finalising your engineering drawings.
Frequently Asked Questions
What is the difference between a strip and pad footing?
A strip footing is a continuous concrete footing running beneath a load-bearing wall, while a pad footing is an isolated block of concrete supporting a single post or column. Many structures use a combination of both.
What depth should my footings be?
Footing depth depends on soil classification, frost depth where relevant, and the loads being supported. This is determined by a structural engineer, typically based on a soil report for your site.
Do I need an engineer for a small foundation?
For anything supporting a habitable structure, a carport, or a significant load, engineering certification is generally required by your local council. Smaller garden structures may not need certification, but it is worth checking with your building surveyor.
Can this calculator handle a mix of strip and pad footings?
Run the calculator once for your strip footing total, and again for your pad footings, then add the two concrete volumes together for your overall total.
Does this include excavation for the footings?
No -- this calculator estimates concrete volume only. Use the Excavation Calculator for excavation volume and truck load estimates.
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Need An Exact Price, Not Just An Estimate?
The Foundation Calculator gives you a fast, useful planning figure. For a fixed, accurate price backed by a site assessment, request a free professional quotation from HPL Construction.
