Foundation Calculator
Estimate concrete volume, block count, and material cost for strip footings, pad footings, and slabs-on-grade. Supports metric and imperial units with waste and cost options.
1. Unit system
2. Foundation type
Sum of all continuous footing runs.
Used to estimate block count.
3. Block & cost options (optional)
Standard CMU is ~0.4 m (16 in) long.
Use local ready-mix price per m³ or per yd³.
Adds extra concrete for spillage and over-excavation.
Results
How the foundation calculator works
This foundation calculator focuses on quantity and cost estimation. It does not perform structural design or code checks. Always consult a qualified structural engineer for final foundation design.
1. Strip (continuous) footing volume
For a continuous footing that runs under load-bearing walls, the concrete volume is:
Volume = Length × Width × Depth
- Length – total run of all footing segments.
- Width – horizontal width of the footing.
- Depth – vertical thickness of the footing.
2. Pad footing volume
For isolated pads under columns:
Volume per pad = Length × Width × Depth
Total volume = Number of pads × Volume per pad
3. Slab-on-grade volume
For a rectangular slab:
Volume = Slab length × Slab width × Slab thickness
4. Waste / contingency
Concrete orders usually include extra volume to cover:
- Over-excavation or uneven subgrade
- Spillage and pump line losses
- Minor changes on site
The calculator applies your selected waste percentage:
Adjusted volume = Theoretical volume × (1 + Waste% / 100)
5. Block count estimation
If you enter wall thickness, block size, and footing length, the tool estimates the number of blocks in one course:
Blocks per course ≈ Footing length ÷ Block length
Courses ≈ Wall thickness ÷ Block height
Total blocks ≈ Blocks per course × Courses
This is a simplified estimate and does not account for openings, corners, or bond patterns.
Typical foundation dimensions (rule-of-thumb only)
Actual sizes must be determined by an engineer based on soil conditions and loads, but common residential values are:
- Strip footing width: 450–600 mm (18–24 in)
- Strip footing depth: 200–300 mm (8–12 in)
- Slab thickness: 100–150 mm (4–6 in)
- Pad footings: 600–1200 mm (2–4 ft) square, depending on column load
Limitations and safety notes
- This tool is for preliminary estimating only.
- It does not check soil bearing capacity, settlement, or uplift.
- It does not design reinforcement or verify building code compliance.
- Always follow local codes and obtain professional engineering advice before construction.
Foundation calculator FAQ
How do I calculate concrete for a strip footing?
Measure the total length of the footing, its width, and depth. Convert all dimensions to the same unit, then multiply: Volume = Length × Width × Depth. The calculator does this automatically and converts to cubic yards or cubic meters.
How much extra concrete should I order?
Most contractors add 5–10% waste. For complex foundations or poor access, you may choose a higher percentage. The tool lets you set any waste value from 0–30% and shows both theoretical and adjusted volumes.
Can I use this for both metric and imperial units?
Yes. Switch between metric (meters, millimeters) and imperial (feet, inches). The calculator converts volumes to m³ and yd³ and shows approximate 80 lb bag counts for small pours.
Does this calculator design the foundation structurally?
No. It only estimates quantities and cost. Structural design must be done by a qualified engineer who considers soil reports, loads, frost depth, and local building codes.
How accurate is the block count?
Block count is a simplified estimate based on wall length, thickness, and block size. It does not account for openings, lintels, or special blocks. Always add a margin and verify with your supplier or mason.