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Concrete footing calculator

Concrete for continuous footings under walls and square pad footings under posts and piers, in one estimate. Enter either or both.

Figures checked October 1, 2026

Continuous (strip) footing

Add up every run. Use 0 if you only have pads.

Pad (spread) footings
%

Over-dug trenches are one reason NRMCA suggests ordering 4–10% extra.

Drawn to scale from your sizes.
1.45 cubic yards

39.1 ft³ including 10% extra

Continuous footing
35.6 ft³
Pad footings
0 ft³
80 lb bags
66
60 lb bags
87

Footings must sit at least 12 in below undisturbed ground and below your local frost line (IRC R403.1.4). Width and depth come from your plans or local code — this tool only does the volume.

The formula

Continuous footing = total length × width × depth Pad footings = number × length × width × depth To order = (continuous + pads) × (1 + extra%)

Worked example

40 ft of footing 16 in wide and 8 in deep is 40 × 1.33 × 0.67 = 35.6 ft³. Four 24 × 24 × 12 in pads add 16 ft³. Together that’s 51.6 ft³; with 10% extra, 56.7 ft³ — 2.1 cubic yards, or 95 bags of 80 lb mix. At that size a ready-mix truck is worth pricing.

Rules the calculator doesn’t check

Footing width and thickness depend on the load, the soil and the wall above them, and they come from your plans or your local code tables. This tool only turns your dimensions into concrete. Two rules apply almost everywhere:

  • Depth: at least 12 in below undisturbed ground, and below the frost line (IRC R403.1.4).
  • Strength: 2,500 psi minimum for foundations not exposed to the weather (IRC Table R402.2); walls exposed to weather need 3,000 psi in moderate and severe climates.

Dig to undisturbed soil

Footings bear on undisturbed or properly compacted soil. Loose spoil in the bottom of a trench settles later — clean it out before you pour.

Reinforcing steel goes in according to your plans; the rebar calculator handles grids and laps.

Questions people ask

How many bags for a 2 × 2 × 1 ft footing?

It’s 4 ft³: 7 bags of 80 lb mix (6.7 rounded up) or 9 bags of 60 lb. Add your extra on top if you’re pouring several.

How deep do footings need to be?

The IRC requires the bottom of a footing to be at least 12 in below undisturbed ground and below the frost line (R403.1.4). Frost depth is set locally — your building department will tell you the number.

What strength of concrete do footings need?

Under the IRC, foundations not exposed to weather need 2,500 psi in every climate (Table R402.2). Standard bagged concrete mix exceeds that — Quikrete rates its Concrete Mix at 4,000 psi at 28 days.

How do I measure a trench that isn’t square?

Measure width and depth every few feet and average them. Trenches are usually wider at the top and deeper in places than planned, and the averages are what you’ll actually fill.

Sources for the numbers on this page

  1. State of Ohio (adopted IRC text) — Residential Code of Ohio 4101:8-4-01 — Table R402.2 minimum compressive strength; R403.1.4 footing depth · checked October 1, 2026
  2. National Ready Mixed Concrete Association — CIP 8 — Discrepancies in yield (ordering 4–10% extra) · checked October 1, 2026
  3. Quikrete — Concrete Mix No. 1101 — technical data sheet (bag yields, strength gain, curing) · checked October 1, 2026
  4. Sakrete — Estimating bagged concrete jobs · checked October 1, 2026

Corrections and updates are logged on the sources page.