Foundation Calculator
Estimate concrete and excavation for strip and raft foundations.
How to use this tool
- Choose strip (perimeter run) or raft (area) footing.
- Enter dimensions (length, width, depth or total area).
- Add wastage and optional cost.
- Calculate concrete volume, excavation volume and cost.
How it works
Strip: perimeter length x width x depth. Raft: area x thickness. Excavation uses the trench dims plus a small allowance; concrete volume includes wastage.
Tips
- Add 10% because trenches are rarely perfectly square.
- Check depth below frost line or to engineer spec.
- Factor trench sides sloped for safety into excavation volume.
Limitations
Structural sizing is not included — a geotechnical/structural engineer must verify design.
Frequently asked questions
How do I measure a strip footing?
Run the total footing length around the building footprint, then multiply by width and depth. Corner overlaps are small but the calculator adds a little for them.
Does the calculator include excavation?
Yes — it can output both the concrete volume you pour and the excavation volume you dig, based on the trench dims.
Can I subtract the inner core of a raft?
A raft is a solid slab; for slab-on-grade use the concrete calculator. This tool handles strip footings and rafts.