Volume formula
length (ft) × width (ft) × depth (in) ÷ 12 ÷ 27 = yd³
Example: 20 × 1.33 × 8 ÷ 12 ÷ 27 = 0.66 yd³ net.
Concrete planning estimate
Concrete Footing Calculator
Calculate concrete volume for strip footings, pad footings, and foundation footings. Enter length, width, and depth to get cubic yards, bag count, and ordering quantity.
What the footing calculator estimates
Enter your footing dimensions and the calculator estimates concrete volume using the rectangular footing formula. Footings are modeled as a uniform rectangular cross-section for the full length.
- Concrete volume in cubic yards (imperial) or cubic meters (metric).
- 40 lb, 60 lb, and 80 lb bag counts for manual mixing.
- Ready-mix recommendation for larger pours.
- Weight estimate for concrete ordering.
- Formula and assumption summary.
Footing concrete formula
Footings use a simple rectangular volume formula. The calculator takes length and width in feet, and depth in inches (imperial).
Assumptions
The formula assumes a uniform rectangular cross-section along the full footing length. It does not account for keyways, stepped footings, or varying widths.
Important note
Footings are structural elements. Minimum dimensions, frost depth, rebar sizing, and concrete strength must meet local building code. Consult an engineer for structural footings.
Common footing size estimates
Pre-calculated for M250 concrete, 5% waste. Width shown in feet for the formula.
| Footing dimensions | Net yd³ | Ordered yd³ | 80 lb bags |
|---|---|---|---|
| 10 ft × 16 in × 8 in | 0.33 | 0.35 | 16 |
| 20 ft × 16 in × 8 in | 0.66 | 0.69 | 32 |
| 30 ft × 16 in × 8 in | 0.99 | 1.04 | 47 |
| 40 ft × 24 in × 12 in | 2.96 | 3.11 | 142 |
| 60 ft × 24 in × 12 in | 4.44 | 4.67 | 212 |
Concrete footing calculator FAQ
How deep do concrete footings need to be?
Footings must extend below the local frost depth to prevent frost heave. In warm climates this may be 12 in; northern US regions may require 36–48 in. Always check local building codes for the minimum frost depth in your area.
How wide should a strip footing be?
A common rule of thumb for residential strip footings is twice the wall width. A typical 8 in block wall footing might be 16 in wide and 8 in deep. Your local building code specifies minimums for your soil and load conditions.
How much concrete for a 20 ft footing?
A 20 ft × 16 in wide × 8 in deep strip footing needs about 0.66 yd³ net — roughly 32 bags of 80 lb concrete with 5% waste.
What concrete PSI should I use for a footing?
3000 psi (M250) is a common minimum for residential footings. Structural or load-bearing footings may require higher strength. Check local code and consult an engineer for structural applications.
Do footings require rebar?
Most building codes require rebar in structural footings. Typical residential strip footings use two or three #4 or #5 bars running longitudinally. Your engineer or local code specifies the requirements.
Is a permit required for footings?
Footing work is almost always permitted — footings support structures and are inspected before backfill. Check with your local building department before starting any footing work.
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Next planning steps
Planning estimates only
These are rough material estimates for planning purposes only. Footings are structural elements. Minimum footing width, depth, rebar sizing, and concrete strength must meet local building code. Consult a licensed structural engineer and obtain the required permits before placing any structural footing.