Concrete Footing Calculator
Estimate concrete for strip footings, deck footings, and small foundation projects. Enter length, width, and depth to get cubic yards, cubic feet, bag counts, waste allowance, and optional cost.
Results are estimates for planning only. Footing requirements depend on soil, frost depth, loads, and local code. Confirm quantities and structural requirements with your supplier, building department, or a qualified professional.
How to calculate concrete for footings
Use Volume = length × width × depth. Because footing depth is usually measured in inches, convert depth to feet first: depth in feet = depth in inches ÷ 12. Divide cubic feet by 27 to estimate cubic yards.
For example, a 20 ft footing that is 1.5 ft wide and 12 in deep is about 30 cubic feet, or about 1.11 cubic yards before waste.
Common footing sizes
| Footing example | Typical planning dimensions | Approximate use |
|---|---|---|
| 8 in × 16 in strip footing | About 0.67 ft wide × 8 in deep | Small walls or light-duty planning examples |
| 12 in × 24 in footing | About 2 ft wide × 12 in deep | Wider strip footing planning |
| Deck post footing | Often round or square and below frost depth | Confirm diameter and depth with local code |
Concrete bag yields
| Bag size | Typical yield | Planning note |
|---|---|---|
| 40 lb | ≈ 0.30 cu ft | More bags, easier handling |
| 60 lb | ≈ 0.45 cu ft | Common general-purpose size |
| 80 lb | ≈ 0.60 cu ft | Fewer bags, heavier lifting |
Add 5–10% for waste, uneven excavation, spillage, and small measurement differences. For larger pours, ready-mix delivery may be more practical than mixing many bags by hand.
Related calculators
Concrete calculator (all shapes) · Concrete slab calculator · Gravel calculator for base or drainage planning
FAQ
How do I calculate concrete for a footing?
Multiply length by width by depth. Convert the depth from inches to feet, then divide cubic feet by 27 to estimate cubic yards.
How deep should a footing be?
It depends on soil, frost depth, loads, and local code. This page only estimates concrete quantity; confirm footing size and depth with your building department or a qualified professional.
How many bags of concrete do I need for footings?
Divide the total cubic feet by the bag yield: about 0.30 cu ft for 40 lb, 0.45 cu ft for 60 lb, or 0.60 cu ft for 80 lb bags. Add waste before buying materials.