Choose the footing type
Continuous mode is for strip footings. Pad mode is for isolated rectangular or square footings.
Concrete & masonry
Concrete Footing Calculator
Estimate concrete volume for continuous strip footings or rectangular pad footings. Add multiple footing sizes, your own extra-material allowance, bag yield, ready-mix ordering increments, and optional material cost.
Quantity estimator only.Enter footing dimensions from your plans, engineer, contractor, or applicable building requirements. This tool does not choose a safe footing width, depth, reinforcement, bearing capacity, or frost depth.
Calculation method
How to calculate concrete for footings
A rectangular footing is a rectangular prism. The calculator first converts every dimension to a consistent internal unit, calculates each footing section, sums the base volume, applies your selected allowance, and only then performs bag or supplier-order rounding.
Enter concrete dimensions
Use the actual concrete length, width, and depth. Excavation depth is not automatically the same as concrete depth.
Add the project allowance
Choose an allowance that reflects your site and project guidance. The calculator applies it after the geometric base volume.
Apply purchase rules
Bags round up to whole bags. Ready-mix rounds only when you enter a real supplier ordering increment.
Concrete footing formulas
One rectangular footing sectionVolume = length × width × concrete depth
Repeated identical footingsSection total = one-footing volume × quantity
Gross project volumeGross volume = sum of all section totals
Verified deduction, when usedBase volume = gross volume − verified deduction
Planning volumeRequired = base × (1 + allowance ÷ 100)
Bagged concreteBags = round up(required volume ÷ yield per bag)
Worked example: continuous strip footing
Suppose a continuous footing is 40 ft long,16 in wide, and 8 in deep.
40 × (16 ÷ 12) × (8 ÷ 12) =35.56 ft3
Dividing by 27 gives about 1.317 yd3 before any extra allowance. With a 10% allowance:
35.56 × 1.10 = 39.11 ft3 ≈ 1.449 yd3
If the supplier accepts orders in 0.25 yd3 increments, the purchase quantity becomes 1.50 yd3. The calculator only makes that final rounding when you explicitly enter the 0.25 yd3 increment.
Worked example: rectangular pad footings
Six identical pads measuring 24 × 24 × 12 in each contain 4 ft3 of concrete per pad:
(24 ÷ 12) × (24 ÷ 12) × (12 ÷ 12) × 6 =24 ft3
With 10% extra, the planning volume is26.4 ft3, or about 0.978 yd3.
How to measure continuous footings
Measure the concrete run length and the intended concrete width and depth. If width or depth changes, create a separate row for each constant section instead of averaging unlike geometry.
For repeated equal runs, use the quantity field. For stepped, sloped, tapered, circular, or otherwise non-rectangular footings, divide the project into suitable verified shapes or use a calculator designed for that geometry.
How to measure pad footings
Enter the plan length, plan width, and concrete depth of the pad. Group identical pads together with the quantity field; use separate rows when pad sizes differ.
This page handles rectangular and square pads. Round piers and post holes use circular geometry and are intentionally outside this calculator's scope.
Allowance and trench variation
The geometric footing volume is based on the dimensions you enter. Real excavations may differ because of over-dig, irregular trench walls or bottoms, form tolerances, spillage, and other site-specific conditions. Use the allowance field as a planning input rather than treating a preset percentage as a universal rule.
If your drawings, contractor, engineer, or concrete supplier specifies a project quantity or allowance, use that project-specific guidance.
Bagged concrete and ready-mix ordering
For bagged concrete, enter the manufacturer-stated yield of one bag. The calculator divides the required volume by that yield and rounds up to complete bags because partial bags cannot normally be purchased.
For ready-mix, the calculator reports the exact planning volume first. It rounds up to a supplier increment only if you enter one. Supplier minimum orders, delivery fees, short-load charges, and jobsite losses are not invented by the calculator.
Footing size is a structural decision
This calculator deliberately does not design the footing. Footing width, depth, bearing area, reinforcement, frost protection, and construction requirements can depend on structural loads, soil, climate, local code, and project-specific engineering.
Use dimensions from the applicable plans or qualified project guidance, then use this calculator to estimate material quantity from those dimensions.
Concrete footing calculator FAQ
How do I calculate concrete for a strip footing?
Multiply the total concrete run length by footing width and concrete depth after converting all dimensions to compatible units. Add separate runs when their dimensions differ.
How do I calculate concrete for pad footings?
Multiply pad length × width × concrete depth, then multiply by the number of identical pads. Use another row for a different pad size.
Does this calculator tell me how wide or deep my footing should be?
No. It estimates concrete quantity from dimensions you already have. Structural footing sizing is outside this calculator's scope.
Should I use excavation depth or concrete depth?
Enter the depth of concrete in the footing. Excavation may include other layers or extra depth that is not filled with footing concrete.
Why does the calculator ask for bag yield?
Yield varies by concrete product and bag size. Using the actual manufacturer-stated yield is more reliable than assuming one universal bag volume.
Why is the ready-mix order increment optional?
Supplier ordering rules vary. Leaving it blank preserves the exact required volume; entering a known increment rounds the order up to that increment.
Can I calculate several footing sizes at once?
Yes. Add multiple rows. The calculator computes each row independently, sums the base volume, and then applies the project allowance.
Can I use Metric units?
Yes. Continuous run length uses meters while cross-section dimensions use millimeters; pad dimensions use millimeters. Results include cubic meters as well as converted Imperial volume.
Does this calculate round piers or post holes?
No. This calculator intentionally covers rectangular strip and pad footing geometry. Circular pier/post-hole geometry belongs in a dedicated calculator.
Can I save or share my footing estimate?
Yes. After a successful calculation, the current project state is stored in the URL so it can be copied, shared, or reopened.
Assumptions and limitations
- Every entered footing section is treated as a rectangular prism.
- Entered dimensions represent concrete dimensions, not structural design recommendations.
- An overlap/void deduction is applied only when the user enters a verified volume; intersections are not auto-detected.
- The allowance percentage is supplied by the user and is applied after verified deductions.
- Bag quantities depend on the manufacturer yield entered.
- Ready-mix rounding occurs only when a supplier increment is entered.
- Cost includes only the entered material price, not delivery, labor, reinforcement, excavation, pumping, forms, taxes, or fees.
- Round, tapered, sloped, stepped, or irregular footing geometry is not automatically modeled.