Practical guide
Foundation Quantities: Strip, Pad and Raft
Measure foundation concrete using the specified geometry. Strips, pads and rafts need different take-offs, but a quantity calculator cannot select a safe foundation type or depth.
Updated 15 October 2026
Reviewed by the 99Tools team. Editorial and corrections policy.
Quick answer: follow the specified shape
For a rectangular strip or pad, volume is length × width × concrete depth in metres. Add different non-overlapping sections. For a raft, count the base slab once and add only the extra ribs or thickenings outside that volume. Apply any agreed allowance after the measured total.
Strip foundations under building walls
Record the concrete width and thickness for each run, together with the measured run length. Use one drawing convention for corners and T-junctions so overlapping concrete is not counted twice. The total length of an external building outline is not automatically the correct footing take-off length.
Square and rectangular pad quantities
A square pad uses equal plan length and width; a rectangular pad does not. Multiply identical pads only when all their dimensions match. For illustration, six 1.2 m × 1.2 m pads with 350 mm concrete depth contain 3.024 m³. These dimensions are an arithmetic example and do not establish a suitable pad design.
Raft base slab and extra concrete
A hypothetical 48 m² base slab at 150 mm contains 7.2 m³. If a separately measured rib adds 0.36 m³ below that slab, total measured concrete is 7.56 m³. Do not add the rib’s entire depth if part of it has already been counted inside the slab. Intersecting ribs also need overlap checks.
Why a depth-of-foundation calculator cannot be universal
Founding level, excavation depth and concrete thickness describe different things. Soil and ground conditions, the supported structure and the chosen foundation design affect them. Enter the specified concrete dimensions after the actual requirements are established; do not use the example defaults as a depth recommendation.
Cement and concrete blocks are different orders
Cement-only bags do not equal bags of complete concrete premix or finished wet concrete. A block or cinder-block wall needs a masonry count using its installed unit dimensions. Its footings and any concrete-filled cores require separate specified quantities.
Keep the quantity and design checks separate
The foundation tool does not calculate soil-bearing capacity, settlement, raft bending, reinforcement or beam-on-elastic-foundation behaviour. Obtain the required design for the site, then use the tool to check its volumes and purchasing assumptions.
Use the related calculators
Apply the explanation above with your own figures. Open a calculator below, check every input and review the result assumptions before making a decision.
Frequently asked questions
Can the calculator choose between strip and raft foundations?
No. Its context choice labels the quantity being entered; it does not recommend a foundation system.
Does raft thickness come from the calculator?
No. Enter the thickness and other dimensions specified for the actual raft.
How do I avoid double counting a raft beam?
Count the base slab once, then add only beam concrete outside that slab volume. Check rib intersections separately.