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Concrete footing calculator

Strip and spread footings — length × width × depth.

Most pours order 5–10% extra for spillage and over-excavation.

Estimated volume

0.66cubic yards· 0.503 m³· 17.78 ft³
Bag sizeYield per bagBags needed
40 lb0.3 ft³60
60 lb0.45 ft³40
80 lb0.6 ft³30
25 kg0.413 ft³44
30 kg0.496 ft³36
Planning estimate. Bag counts assume the yields above; check the yield printed on your bag, and allow extra for over-excavation and spillage. Structural and load-bearing work must follow your local building code and an engineer's specification.

Premium · cost estimator

What this pour costs

Bagged
$195.00
30 × 80 lb
Ready-mix
$115.50
0.7 yd³ ordered

Prices are yours to set and stay in this browser. Ready-mix suppliers usually have a minimum load and a short-load surcharge — check before comparing.

Premium · project

Multi-pour project & order sheet

Add this pour to a saved project to total several pours into one order, then print a clean order sheet with the bag counts and yardage to hand your supplier.

Projects are stored in this browser only — nothing is uploaded and there is no account.

Formwork

How the volume is measured

wall aboverun / lengthdepthwidth acrossSTRIP FOOTING

How this calculator works

A strip footing is a long rectangular prism under a wall; a spread footing is a pad under a column. Either way the volume is length × width × depth. Enter the total run of the footing as the length, and the trench cross-section as width × depth.

The volume is then converted to cubic yards (27 cubic feet to the yard) and cubic metres, and divided by each bag's yield to give a bag count — always rounded up, since you cannot buy part of a bag. Bag yields follow the published premix figures: 0.30 ft³ for a 40 lb bag, 0.45 ft³ for 60 lb and 0.60 ft³ for 80 lb, with metric bags scaled from the same mixed density.

Add a waste allowance for anything real: over-excavated trenches, uneven sub-grade, spillage and what stays in the mixer. Five to ten percent is typical; a rough excavation can need more.

Worked examples

Common footing sizes, already calculated

Concrete for a 10 ft footing, 16×8 in0.33 yd³15 × 80 lb bagsConcrete for a 10 ft footing, 24×12 in0.74 yd³34 × 80 lb bagsConcrete for a 15 ft footing, 16×8 in0.49 yd³23 × 80 lb bagsConcrete for a 15 ft footing, 24×12 in1.11 yd³50 × 80 lb bagsConcrete for a 20 ft footing, 16×8 in0.66 yd³30 × 80 lb bagsConcrete for a 20 ft footing, 24×12 in1.48 yd³67 × 80 lb bagsConcrete for a 24 ft footing, 16×8 in0.79 yd³36 × 80 lb bagsConcrete for a 24 ft footing, 24×12 in1.78 yd³80 × 80 lb bagsConcrete for a 30 ft footing, 16×8 in0.99 yd³45 × 80 lb bagsConcrete for a 30 ft footing, 24×12 in2.22 yd³100 × 80 lb bagsConcrete for a 40 ft footing, 16×8 in1.32 yd³60 × 80 lb bagsConcrete for a 40 ft footing, 24×12 in2.96 yd³134 × 80 lb bags

Other pours

More calculators

SlabPatios, floors, driveways and pads — length × width × thickness.ColumnRound columns and sonotube piers — π·r²·height.Post holesFence and deck post footings — hole volume, less the post.StepsSolid poured stairs — stacked step cross-sections × width.CurbCurbs and curb-and-gutter — cross-section × run.