Concrete Footing Calculator — Strip & Pad Footings
Calculate concrete volume for strip footings and pad footings, with a simplified rebar estimate and formwork area. Enter footing width, depth and run length to get the volume to order for walls, extensions and garden structures.
Free to try — no sign-up
Plan the whole job — not just this calculation
Save results to a project: budget and shopping list build themselves, and the whole plan exports as a PDF. Draw your floor plan and room sizes pre-fill the calculators.
How the footing volume is calculated
- 1Strip footing: width × depth × run length per run; sum all runs
- 2Pad footing: length × width × depth per pad
- 3Add 10% for over-dig and spillage — trench sides are never perfectly straight
- 4Rebar (simplified): two longitudinal bars per strip plus 5% laps; actual reinforcement must be designed locally
- 5Footing depth: below local frost depth — this varies enormously by region
- 6Formwork: 2 × depth × run length where the footing is formed above ground
Worked example
Strip footing for a garage: 24 m perimeter, 500 mm wide × 250 mm deep.
Volume: 24 × 0.5 × 0.25 = 3.0 m³. With 10%: 3.3 m³ of ready-mix. Rebar at 2 bars per run: 48 lm plus laps.
Frequently asked questions
How deep do concrete footings need to be?
Below the local frost line — from 450 mm in mild climates to 1.2 m or more in cold regions — and always into undisturbed load-bearing ground. Your local building authority publishes the required depth.
How wide should a footing be for a wall?
A common minimum is 3× the wall thickness — a 215 mm masonry wall needs at least a 650 mm wide footing. Poor soils need wider footings; a structural engineer sizes anything load-bearing.
Should I use bags or ready-mix for footings?
Ready-mix above about 1 m³ — footings need to be poured in one continuous operation, and hand-mixing 100+ bags risks cold joints. Small pads and post footings suit bags.
Do footings need rebar?
Mass-concrete strip footings on stable ground often don't. Pad footings, stepped footings and anything on soft or shrinkable soils normally do. This is a structural design question — get it specified.
What concrete mix for footings?
C25/30 (GEN3-type) is the common specification for domestic footings. Sulphate-bearing soils need sulphate-resistant cement — a soil check is worth it before ordering.