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Concrete Footing Calculator

Calculating structural foundation concrete demands computing continuous perimeter strip footings alongside isolated interior pier pads and column foot

Construction
ft
Total perimeter length of strip footing trench in feet
in
Trench width in inches (assumed standard residential: 16-24 in)
in
Footing thickness in inches (assumed standard: 8-12 in)
Number of individual square column/pier post footings
%
Earthen trenches bulge and cave; 10-15% over-excavation buffer recommended
Formula & Methodology
Strip Footing Volume (cu ft) = Trench Length (ft) × (Width in ÷ 12) × (Depth in ÷ 12) Pier Pad Volume (cu ft) = Pier Count × (Pad Length in ÷ 12) × (Pad Width in ÷ 12) × (Pad Depth in ÷ 12) Total Net Volume (cu yd) = (Strip Volume cu ft + Pier Volume cu ft) ÷ 27 Gross Order Quantity (cu yd) = ⌈Total Net Volume × (1 + Waste % ÷ 100) ÷ 0.25⌉ × 0.25

Continuous footings form a rectangular prism along the foundation perimeter trench, while pier pads distribute vertical point loads beneath support posts. Because footings are poured directly into earthen trenches without finished forms, trench wall cave-ins and subgrade irregularities require a 10% to 15% waste allowance. All dimensions are normalized to feet before volume aggregation and rounded strictly up to the nearest ready-mix batch increment.

Total Footing Concrete to Order

2.5 cu yd

Overview

Calculating structural foundation concrete demands computing continuous perimeter strip footings alongside isolated interior pier pads and column footers. This Concrete Footing Calculator computes dual-geometry footing requirements with explicit depth conversions and an over-excavation waste reserve.

Estimates are for material planning and budgeting purposes only. This calculator does not provide structural engineering, architectural design, or official building code compliance advice. Always verify measurements, local building codes, and permit requirements with a licensed contractor or local building authority before purchasing materials or commencing construction.

Worked Examples

Example 1: Continuous Strip Trench with 4 Pier Pads (Check Case)

Inputs: Trench Length = 50 ft, Width = 16 in, Depth = 8 in, Piers = 4 (24"×24"×12"), Waste = 10%

  1. Convert strip dimensions: Width = 16 ÷ 12 = 1.3333 ft; Depth = 8 ÷ 12 = 0.6667 ft.
  2. Calculate strip footing volume: 50 ft × 1.3333 ft × 0.6667 ft = 44.44 cu ft = 1.646 cu yd.
  3. Calculate single pier pad: (24÷12) × (24÷12) × (12÷12) = 2 ft × 2 ft × 1 ft = 4.00 cu ft.
  4. Calculate 4 pier pads: 4 × 4.00 cu ft = 16.00 cu ft = 0.593 cu yd.
  5. Sum net volume: 44.44 + 16.00 = 60.44 cu ft ÷ 27 = 2.239 cu yd.
  6. Add 10% trench waste: 2.2387 × 1.10 = 2.4625 cu yd.
  7. Round UP to next 0.25 cu yd truck increment: 2.50 cu yd.
Final Answer: 2.50 cu yd to order (1.65 strip cu yd + 0.59 pier cu yd; exact unrounded: 2.46 cu yd)

Example 2: Perimeter Strip Footing Only (100 ft × 20 in × 10 in with 12% Waste)

Inputs: Trench Length = 100 ft, Width = 20 in, Depth = 10 in, Piers = 0, Waste = 12%

  1. Convert trench width and depth: Width = 20 ÷ 12 = 1.6667 ft; Depth = 10 ÷ 12 = 0.8333 ft.
  2. Calculate volume: 100 × 1.6667 × 0.8333 = 138.89 cu ft.
  3. Convert to cubic yards: 138.89 ÷ 27 = 5.1440 cu yd.
  4. Add 12% trench over-dig allowance: 5.1440 × 1.12 = 5.7613 cu yd.
  5. Round UP to supplier increment: 6.00 cu yd.
Final Answer: 6.00 cu yd to order (5.14 net cu yd + 0.62 waste reserve; 6.00 cu yd ordered)

Example 3: Heavy Deck Footings (6 Pier Pads at 30" × 30" × 12" Deep)

Inputs: Trench Length = 1 ft (minimal), Width = 12 in, Depth = 6 in, Piers = 6 (30"×30"×12"), Waste = 10%

  1. Single pier pad: 2.5 ft × 2.5 ft × 1.0 ft = 6.25 cu ft.
  2. Total 6 pads: 6 × 6.25 cu ft = 37.50 cu ft = 1.3889 cu yd.
  3. Add 10% waste buffer: 1.3889 × 1.10 = 1.5278 cu yd.
  4. Round UP to next 0.25 yd: 1.75 cu yd.
Final Answer: 1.75 cu yd to order (1.39 net cu yd for pier pads; 1.75 cu yd ordered)

How to Use This Calculator

  1. Enter total linear length of your continuous trench footing in feet.
  2. Enter continuous trench width and thickness in inches (common residential sizes are 16 in wide by 8 in deep).
  3. Enter the count of isolated square pier pads needed for columns or porch posts.
  4. Select the pier pad dimensions from the presets.
  5. Review the line-item breakdown showing strip footing volume, pier pad volume, and rounded order quantity.

Reference Table

Footing ConfigurationTrench DimensionsPier PadsNet VolumeReady-Mix Order (10% Waste)
50 ft Strip + 4 Pads16" W × 8" D4 @ 24"×24"×12"2.24 cu yd2.50 cu yd
80 ft Strip Only16" W × 8" D0 pads2.63 cu yd3.00 cu yd
100 ft Strip + 6 Pads16" W × 8" D6 @ 24"×24"×12"4.18 cu yd4.75 cu yd
100 ft Strip + 6 Pads20" W × 10" D6 @ 24"×24"×12"6.03 cu yd6.75 cu yd
120 ft Strip Only20" W × 10" D0 pads6.17 cu yd7.00 cu yd
150 ft Strip + 8 Pads24" W × 12" D8 @ 30"×30"×12"15.19 cu yd17.00 cu yd

Frequently Asked Questions

How deep must residential concrete footings be placed?
Building codes require footings to extend below the local maximum frost penetration depth (ranging from 12 inches in southern US regions to over 48 inches in northern zones) to prevent winter frost heaving. Confirm depth with local building authorities.
Why do earthen footing trenches require a higher waste factor?
Unlike wooden formwork, backhoe trenches have irregular earthen side walls that bulge outward under the hydraulic pressure of wet concrete. Excavation sloughing and uncompacted trench bottoms commonly consume 10% to 15% extra volume.
What is the rule of thumb for footing width and depth?
In typical residential light-frame construction, footings are generally sized so the width is twice the thickness of the foundation wall it supports (e.g., a 16-inch wide footing for an 8-inch wall), with a minimum thickness equal to the wall thickness (typically 8 inches).
Should rebar be elevated off the ground in footing trenches?
Yes. Rebar must never rest on soil. Building codes require reinforcement steel to be supported on concrete chairs or dobies to maintain at least 3 inches of clear concrete coverage between steel and undisturbed earth.
Can I pour continuous footings and pier pads from the same truck?
Yes. Contractors routinely pour strip perimeter trenches and isolated column pads during the same concrete dispatch, which helps satisfy truck minimum capacity and avoids short-load fees.

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Reviewed & Authored by: OnlineConvers Construction & Estimation Team · Last Updated: 2026-10-09
Calculations compute continuous trenches as rectangular prisms (Length × Width × Depth) and isolated pier pads as discrete line items. All dimensions in inches are converted to feet (in ÷ 12) prior to multiplication. Volumes are summed, augmented by a trench over-dig waste factor, and rounded strictly UP to the next 0.25 cubic yard increment. This model serves material planning only and is not structural engineering advice.