Measure the trench after excavation
Plan dimensions are a starting point, but real trenches often get wider or deeper during digging. Measure formed or excavated width, depth, and total run before finalizing the order.
concrete
Concrete Footing Calculator
Estimate concrete yards and bags for continuous strip footings.
Estimated concrete neededLength, width, and thickness are required before the estimate appears.
Example40 ft footing x 2 ft wide x 10 in = about 2.47 yd³
Check local footing width, frost depth, and code requirements before ordering.
Last reviewed: May 12, 2026 by the BuilderCalc editorial team.
SSR formula reference
Concrete Footing Calculator formulas
These formulas are rendered in the server HTML so crawlers, LLMs, and users can read the method without running JavaScript. The interactive calculator can change the inputs, but the estimating math below is visible in the raw page source.
Volume (cubic feet) = Length x width x thickness (in inches / 12).
Volume (cubic yards) = Cubic feet / 27.
Bags (80-lb) = Cubic feet / 0.60, rounded up.
80-lb bag yields about 0.60 ft3, or 0.022 yd3.
| Result | Formula |
|---|---|
| Volume in cubic feet | Length x width x thickness in feet |
| Thickness in feet | Thickness in inches / 12 |
| Volume in cubic yards | Cubic feet / 27 |
| 80-lb bags | Cubic feet / 0.60, rounded up |
| Ready-mix order | Cubic yards x (1 + waste percent) |
Standard PSI by application
| Application | Recommended PSI |
|---|---|
| Patio or walkway | 3,000 PSI |
| Garage floor, residential | 3,500 PSI |
| Driveway, cars | 3,500 to 4,000 PSI |
| Driveway, trucks or RVs | 4,000 to 4,500 PSI |
| Foundations and footings | 3,000 to 4,000 PSI, per plan and code |
Bag yield reference
| Bag size | Common yield |
|---|---|
| 80-lb bag | About 0.60 ft3, or 0.022 yd3 |
| 60-lb bag | About 0.45 ft3, or 0.017 yd3 |
| 50-lb bag | About 0.375 ft3, or 0.0138 yd3 |
| 40-lb bag | About 0.30 ft3, or 0.011 yd3 |
Footing planning
Concrete Footing Calculator planning notes
Footings are code-sensitive work. Use the calculator to estimate volume, then confirm width, depth, frost requirements, soil conditions, and reinforcement before ordering.
Keep frost depth separate from volume
The calculator estimates concrete quantity. It does not decide bearing capacity, frost protection, or footing design. Those requirements come from local code and site conditions.
How to use it
Keep the estimate tied to field measurements
Measure trench dimensions
Use the actual excavated or formed length, width, and depth. Real trenches often differ from plan dimensions.
Check code requirements
Confirm frost depth, bearing needs, reinforcement, and inspection requirements before treating the volume as final.
Order with waste
Add waste after measuring the trench so over-dig, rough edges, and form variation are covered.
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FAQ
Concrete estimating questions
How do I calculate concrete for a footing?
Multiply footing length by width by depth, all in feet, then divide cubic feet by 27 to get cubic yards. Add waste after measuring the excavated or formed trench.
What size footing should I use?
Footing size depends on load, soil bearing, frost depth, and local code. The calculator estimates volume only; it does not size a structural footing.
Should footing depth include frost depth?
The volume should include the actual concrete depth being poured. Whether the footing must extend below frost depth is a local code and design question.
Do footings need rebar?
Many continuous footings use reinforcement, but bar size and spacing depend on the design. Confirm the layout before ordering concrete.