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Concrete Footing Calculator

By · Updated Aug 2026

Estimate concrete volume, bags, and supply cost for strip footings, pads, piers, and post holes using dimensions from your plan.

ft
in
in
How to measureDiagram and scope
Choose bag yield80 lb (36.3 kg)

Use the mixed yield printed on the product label when it differs from the preset.

Add material pricingNo price
$
$per yd³
$

Supply cost only. Labor, excavation, forms, reinforcement, pumping, permits, and installation are excluded.

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How to Use

  1. Choose the footing type - Select a continuous strip, rectangular pad, or round pier/post footing.
  2. Enter approved dimensions - Use dimensions from the plan, engineer, or local building authority; this calculator does not design the footing.
  3. Enter quantity and waste - Count identical footings and choose an overage for excavation variation, spillage, and measurement uncertainty.
  4. Confirm the bag yield - Use a common preset or enter the mixed yield printed on the concrete bag.
  5. Review the order estimate - Compare cubic yards, bag counts, per-footing volume, waste, conversions, and optional supply pricing.
Quick answer

A 20 ft continuous footing that is 16 in wide and 8 in thick uses about 0.66 yd³ before waste, or about 0.72 yd³ and 33 standard 80 lb bags with 10% overage. A 12 in diameter round pier that is 36 in deep uses about 0.087 yd³ before waste, or 5 standard 80 lb bags with 10% overage. Select the footing geometry above and enter the dimensions required by your approved plan.

Concrete Footing Volume Formulas

The calculator first finds the volume of one footing, multiplies by the number of identical footings, and then adds the selected waste allowance:

Continuous / strip footing = Run length × width × concrete thickness
Rectangular / square pad = Length × width × concrete thickness
Round pier or post footing = π × (diameter ÷ 2)² × concrete depth
Round footing with post deduction = π × [(hole radius)² − (post radius)²] × concrete depth
Project total = Volume per footing × quantity
Concrete to order = Project volume × (1 + waste percentage)
Cubic yards = Cubic feet ÷ 27
Bag count = Concrete to order ÷ mixed yield per bag, rounded up

The excavation depth below grade is not automatically the concrete thickness. Enter the actual concrete dimensions shown on the project details.

Material Estimate, Not Footing Design

This calculator estimates concrete for dimensions you already know. It does not determine the required footing width, thickness, depth below grade, pier spacing, soil bearing capacity, structural load capacity, frost protection, or reinforcement.

Use dimensions from approved plans or confirm them with the local building authority or a qualified professional. Local requirements can vary with climate, soil, structure, and the code adopted by the jurisdiction.

Common Concrete Bag Yields

Bag weight does not replace the product yield printed on the package. These presets match the approximate mixed yields published for standard QUIKRETE Concrete Mix; specialty and high-yield products can differ:

Bag SizeApproximate Mixed YieldApproximate Liters
40 lb (18.1 kg)0.30 ft³8.5 L
50 lb (22.7 kg)0.375 ft³10.6 L
60 lb (27.2 kg)0.45 ft³12.7 L
80 lb (36.3 kg)0.60 ft³17 L

Use the custom-yield option when the selected product label gives a different mixed volume. The calculator always rounds the purchase quantity up to whole bags.

How to Measure Each Footing Type

Continuous or strip footing: enter the total concrete run length, the footing width, and the concrete thickness. Do not use trench depth below grade as the concrete thickness unless the footing detail actually calls for concrete through that full depth.

Rectangular or square pad: enter the pad length, pad width, and concrete thickness. Use the quantity field for identical isolated pads.

Round pier or post footing: enter the inside diameter of the hole or form and the concrete depth. Leave post deduction off unless a post occupies part of the concrete volume. For cardboard form-tube planning, the sonotube calculator remains the specialist tool.

For irregular excavations, measure several locations and use a reasonable waste allowance. Soil collapse, loose sides, over-excavation, spillage, and material left in the mixer can all increase the amount required.

Worked Quantity Examples

Known DimensionsQuantityBase VolumeWith 10% Waste80 lb Bags
Strip: 20 ft × 16 in × 8 in1 run0.658 yd³0.724 yd³33
Pad: 3 ft × 3 ft × 12 in4 pads1.333 yd³1.467 yd³66
Round: 12 in diameter × 36 in deep6 piers0.524 yd³0.576 yd³26
Round: 10 in diameter × 36 in deep10 piers0.606 yd³0.667 yd³30

These examples estimate material for the stated dimensions; they are not footing-size recommendations. Bag counts use 0.60 ft³ per 80 lb bag and round upward after waste.

Bagged Concrete or Ready-Mix?

Bag counts are useful for small pads, post holes, and isolated repairs. As the number of bags grows, compare the labor, mixer capacity, placement time, access, and supplier terms against ready-mix delivery.

The optional pricing section compares supply cost only. Ready-mix suppliers may apply minimum orders, short-load charges, delivery limits, waiting time, and pumping fees. Bagged products also vary by yield and local price, so verify both the package label and supplier quote.

Common Footing Estimate Errors

The most common mistakes are using trench depth instead of concrete thickness, forgetting repeated pads or piers, entering outside dimensions instead of the inside form dimensions, assuming every bag has the same yield, and rounding bags before waste is added.

For round holes, the optional post deduction reduces volume only when enabled. Do not deduct reinforcing steel, small anchor hardware, or minor embedded items; their displacement is usually insignificant compared with excavation uncertainty.

Related Calculators

Ready-Mix Concrete CalculatorDelivered concrete for big footing runs.Cement CalculatorMix your own footing concrete.Aggregate CalculatorCrushed stone under the footing.Retaining Wall CalculatorWalls that sit on footings.

Code & Source Notes

  • QUIKRETE Concrete Mix technical data lists approximate mixed yields of 0.30 ft³ for 40 lb, 0.375 ft³ for 50 lb, 0.45 ft³ for 60 lb, and 0.60 ft³ for 80 lb bags. Product-specific yields can differ, so use the package label when available.QUIKRETE Concrete Mix No. 1101 Technical Data
  • Residential footing dimensions and frost protection are governed by the code adopted by the local jurisdiction and the project conditions. This calculator therefore requires the user to supply the approved dimensions rather than generating structural sizes.IRC R403.1 - General (Footings)

After You Size the Footing

Footing volume is the first number of the foundation stage. The usual order from here:

  1. Plan the reinforcementMost jurisdictions want at least two continuous bars in wall footings - work out lengths and laps.
  2. Decide bags vs ready-mixUnder about a yard, bags win; past that, price a short-load delivery.
  3. Size the slab aboveIf a slab sits on the footings, its pour is a separate volume.

Footings support slabs, posts, and walls. Browse the construction calculator collection for all concrete tools.

Frequently Asked Questions

How do I calculate concrete for a continuous footing?
Multiply the total run length by the concrete width and thickness, convert the result to cubic yards or cubic meters, then add the selected waste allowance. Use concrete dimensions from the approved footing detail, not the total trench depth unless the trench is filled completely with concrete.
How do I calculate concrete for round deck footings or post holes?
Use the round pier/post mode. Enter the inside hole or form diameter, the concrete depth, and the number of identical footings. The calculator applies the cylinder formula and returns per-footing volume, project volume, cubic yards, and bags. It does not determine the required diameter, depth, or spacing.
Should I subtract the post from the concrete volume?
Only when the post physically occupies part of the filled hole and the deduction is meaningful. The option is off by default because some footings use forms, brackets, or posts installed after the concrete is placed. Minor steel and hardware displacement normally does not need a deduction.
How many cubic feet does a bag of concrete make?
Standard concrete-mix yields are commonly about 0.30 ft³ for a 40 lb bag, 0.375 ft³ for a 50 lb bag, 0.45 ft³ for a 60 lb bag, and 0.60 ft³ for an 80 lb bag. Specialty and high-yield products differ, so the package label should control the estimate.
How much extra concrete should I order for footings?
Ten percent is a common planning allowance, but accurately formed work may need less and rough excavations may need more. Consider irregular hole sides, soil collapse, over-excavation, spillage, and concrete left in equipment. The calculator supports 0%, 5%, 10%, 15%, or a custom allowance up to 50%.
Does this calculator determine footing size or frost depth?
No. It estimates concrete only after you enter the footing dimensions. Required width, thickness, depth below grade, frost protection, spacing, soil capacity, and reinforcement depend on the project and local requirements and must come from approved plans or qualified guidance.
Does the cost result include labor and excavation?
No. Optional pricing compares bagged-concrete and ready-mix supply costs using the prices you enter. It excludes excavation, forms, reinforcement, placement labor, equipment, pumping, permits, inspections, and other installed-project costs.
Updated Aug 2026 · See our Methodology
This calculator estimates concrete quantity and optional supply cost for dimensions entered by the user. It does not design footing size, depth, spacing, frost protection, soil capacity, or reinforcement. Verify project dimensions, product yield, delivery terms, and local requirements before ordering or construction.