Concrete Footing Calculator
Concrete volume and bag count for strip, spread, stepped, or continuous footings. Pick an application preset for typical sizes, or enter your own dimensions.
Results
Estimates only. Verify dimensions on site, set footings below your local frost line on undisturbed soil, and check building code for required width, depth, and rebar. TakeoffCalc isn't responsible for material over- or under-orders.
How to use this calculator
- 01Pick an Application preset to fill typical dimensions, or leave it on Custom to enter your own. The presets cover the most common footing sizes: light residential strip, 2-story strip, deck pier, fence post, and shed perimeter.
- 02Choose a Footing Type. Strip and Continuous run under walls. Spread is a single rectangular pad under a column or post. Stepped is for sloped sites where the footing changes depth in segments. The math is the same for all four. The type affects the dimension labels and guidance.
- 03Enter Length in feet (or meters), plus Width and Depth in inches (or centimeters). For multiple identical footings (deck piers, fence posts), set Number of Footings. The calculator returns the project total in one shot.
- 04Pick your Bag Size and Waste Factor. 80-lb (36-kg) bags are standard for footings. 10% waste covers the partial-bag overage that can’t be returned. For projects over ~1 cubic yard (0.76 m³), ready-mix delivery is usually cheaper than bags. If your plans include reinforcing bars, estimate them separately with the Rebar Calculator.
- 05Read the results. Total Concrete Needed includes waste and is the orderable cubic yardage. Total Bags is computed from total volume directly, so it can be slightly less than per-footing bags multiplied by the count. That’s normal and reflects actual minimum demand.
Understanding the math
Every footing is a rectangular volume: length × width × depth. Length is given in feet. Width and depth come in inches and need to be converted:
volume ft³ = (lengthFt × widthIn × depthIn) / 144 · yards = ft³ / 27 metric: volume m³ = lengthM × widthM × depthM (all in meters)
For multi-footing projects, multiply the per-footing volume by the count to get total cubic feet. Total bag count is computed from total volume directly, not by multiplying per-footing bags by the count. That single ceiling step gives the actual minimum bag demand, which can be slightly lower because per-footing rounding inflates each footing independently.
Worked example: a 30-foot strip footing at 16″ wide × 8″ deep (9 m × 40 cm × 20 cm), single run, 80-lb (36-kg) bags, 10% waste. Volume = (30 × 16 × 8) / 144 = 26.67 cubic feet (0.76 m³), or 0.99 cubic yards (0.76 m³). With 10% waste: 1.09 cubic yards (0.83 m³). Bags = 26.67 × 1.10 / 0.6 = 48.89, rounded up to 49 bags. Weight = 26.67 × 150 = 4,000 lbs (1,815 kg).
Footing reference chart
Volume and 80-lb bag count for common footing applications, computed at 10% waste. Per-foot rows are for strip footings. Multiply by your trench length to get the project total.
| Application | Dimensions | Volume | 80-lb Bags |
|---|---|---|---|
| Light residential strip | per ft × 16″ × 8″ | 0.036 yd³/ft | 2/ft |
| 2-story residential strip | per ft × 24″ × 10″ | 0.068 yd³/ft | 4/ft |
| Deck pier (rectangular) | 2 ft × 24″ × 12″ | 0.16 yd³ | 8 |
| Fence post | 12″ × 12″ × 36″ | 0.12 yd³ | 6 |
| Light pole / mailbox | 18″ × 18″ × 36″ | 0.28 yd³ | 13 |
| Shed perimeter strip | per ft × 12″ × 8″ | 0.027 yd³/ft | 2/ft |
| Heavy spread footing | 3 ft × 36″ × 18″ | 0.55 yd³ | 25 |
Frequently asked questions
How to calculate concrete footings?
A footing is a rectangular volume: length × width × depth. Multiply all three in feet, then divide by 27 to convert cubic feet to cubic yards. For a 30-foot strip footing at 16″ wide × 8″ deep (9 m × 40 cm × 20 cm): 30 × 1.333 × 0.667 = 26.7 cubic feet (0.76 m³). That works out to 0.99 cubic yards (0.76 m³). Add 5-10% waste because concrete is wet and unforgiving. Partial trucks can't be returned. The calculator above handles unit conversion and waste.
How deep should a footing be?
Footing depth depends on frost depth, soil conditions, and structural load. Many residential footings need to reach below the local frost line and bear on undisturbed soil, but requirements vary by jurisdiction and project. Check your plans and local code before pouring.
How wide should a footing be?
A common planning rule is to make the footing wider than the wall it supports, often around twice the wall thickness for simple residential work. Actual width depends on soil bearing capacity, wall load, local code, and the project plans.
What is the difference between a strip footing and a spread footing?
A strip footing (also called a continuous footing) is a long, narrow trench under a wall, spreading the wall's load along its entire length. A spread footing (or pad footing) is a square or rectangular pad under a single column, post, or pier, concentrating the load through one isolated point. Strip footings support walls. Spread footings support columns. Most residential foundations use strip footings under perimeter walls and spread footings under interior posts.
Do footings need rebar?
Many structural footings use rebar, but the exact bar size, spacing, cover, and layout depend on the footing type, soil, loads, local code, and project plans. Small non-structural footings may have different requirements. Verify with local code or a qualified professional before pouring.
How do I calculate concrete for a stepped footing?
Stepped footings are used on sloped sites where one continuous depth would mean excessive digging. Calculate each step segment as a separate rectangular footing, then add the volumes together. For example: three steps of 10 ft × 16″ × 8″ (3 m × 40 cm × 20 cm) at the lowest level, 10 ft × 16″ × 16″ (3 m × 40 cm × 40 cm) at the middle, and 10 ft × 16″ × 24″ (3 m × 40 cm × 60 cm) at the top. The calculator above handles single rectangular sections. For stepped footings, calculate each step separately and sum the results.
Can I use this calculator with metric measurements?
Yes. Switch the unit selector to Metric and the inputs, bag options, results, reference values, and examples update to metric units where applicable.
Related calculators
Concrete Calculator
Cubic yards, bags, and weight of concrete for slabs, footings, columns, or stairs.
Concrete Block Calculator
Block count, mortar bags, and optional concrete fill for hollow-block walls.
Sonotube Concrete Calculator
Concrete volume, bags, and weight for cylindrical pier forms. Multi-tube projects supported.