Footing Concrete Calculator

Getting Footing Concrete Volume Right the First Time

Accurate volume estimation for concrete footings is essential to establish a strong structural foundation without costly over-ordering. This calculator handles both continuous strip footings (rectangular) and isolated pier bases (circular) in one place. For the full set of strip, pad, and continuous-footing formulas with worked examples, see our pillar guide on concrete footing calculations. To buy by the sack, our guide to how many bags of concrete a footing needs gives counts; for the steel, see our rebar sizing & spacing reference; and for tied slabs, our guide on how to calculate concrete for a slab.

What sets this tool apart: it switches between rectangular/square and circular geometry in one place, accepts meters, centimeters, feet, or inches without manual conversion, and adds a waste allowance (typically 5–10%) so over-excavation and placement losses don't leave you short. Results display in m³, yd³, or ft³ behind a Calculate click, include a yd³ ordering helper at +5%/+10% for supplier rounding, and export to a printable summary for site approvals and purchase orders.

Worked Example: A 10 × 2 × 1.5 ft Strip Footing

Consider a continuous strip footing beneath a bearing wall: 10 ft long, 2 ft wide, and 1.5 ft deep — a common residential dimension for a footing under a block foundation wall. On the Rectangular tab, volume is Length × Width × Depth: 10 × 2 × 1.5 = 30 ft³. Converting to cubic yards, 30 ÷ 27 = 1.11 yd³ net. Footings commonly need a 10% waste allowance to cover over-excavation and trench irregularities: 1.11 × 1.10 = 1.22 yd³ with waste — the figure to phone in to the ready-mix plant.

For a round pier or deck-post footing, switch to the Circular tab. A 12-inch diameter pier poured 36 inches deep has a radius of 0.5 ft and a depth of 3 ft: π × 0.5² × 3 = 2.36 ft³ — small enough that bagged concrete makes sense, at roughly four 80 lb bags (0.6 ft³ yield each) rather than a ready-mix order.

The Footing Volume Formula

• 1) Rectangular / Square FootingVolume = Length × Width × Depth (Thickness)
  Inputs are converted to meters internally before multiplication to keep units consistent.
• 2) Circular FootingVolume = π × r² × Depth, where r = Diameter ÷ 2
• 3) Waste AllowanceAdjusted Volume = Raw Volume × (1 + Waste%)
  Typical waste for footings is 5–10% depending on excavation, formwork, and placement method.
• 4) Display Conversions1 m³ = 35.3147 ft³
  1 m³ = 1.30795 yd³
  yd³ = ft³ ÷ 27

Typical Footing Dimensions

Concrete footings come in a few standard configurations: strip / continuous footings run beneath load-bearing walls (enter the full wall length as L on the Rectangular tab); isolated / spread (pad) footings support a single column (L × W × D, multiplied by quantity for repeated pads); circular / pier footings serve deck posts and pier-and-beam systems (Circular tab, π × r² × D); combined footings merge two or more columns onto one slab where individual pads would overlap; stepped footings step down sloping grade, calculated as separate rectangular segments and summed; and pile caps transfer a column load onto a group of piles, sized as a rectangular prism.

For continuous strip footings, concrete scales with length. The table below shows the volume per linear foot for common width × depth combinations, plus the total for a 10-foot run, so you can sanity-check the calculator at a glance.

Isolated pad footings are simpler: enter Length × Width × Depth directly on the Rectangular tab. For round deck or pier footings, switch to the Circular tab — a 12" diameter × 36" deep pier needs about 2.36 ft³ (≈ four 80 lb bags).

Why Footing Pours Come Up Under

• Skipping the waste allowance. Footings routinely need 5–10% added on top of the raw L × W × D or π × r² × D figure to cover over-excavation, trench irregularities, and placement losses — order the raw volume and the load can come up short before the pour is finished.
• Guessing at frost-line depth. Footings must bear on undisturbed soil and extend below the local frost line — often 12 to 48 inches depending on climate zone. Enter the depth your local building department requires, not a rounded guess, before locking in the volume.
• Running a circular pier footing through the Rectangular tab. Pier and deck-post footings are circular (π × r² × D), not L × W × D. A 12-inch diameter pier poured 36 inches deep needs about 2.36 ft³ — roughly four 80 lb bags — a figure the Rectangular tab cannot produce correctly.
• Forgetting to multiply isolated pads by quantity. A single pad-footing calculation covers one column. Repeated pads under multiple posts must be multiplied by the pad count, or the ready-mix order will only cover the first one.

Mix & Placement Standards

Footing depth must extend below the local frost line per IRC R403.1.4 and soil bearing capacity must be confirmed by a licensed geotechnical or structural engineer before sizing footing dimensions and concrete volume.