Free calculator

Post hole calculator

Fence and deck post footings — hole volume, less the post.

Hole diameter

Hole depth

Number of holes

Post width (0 = none)

A nominal 4×4 post is 3.5 in actual. Enter 0 for a mass footing.

Post depth (0 = none)

Waste / spillage allowanceMost pours order 5–10% extra for spillage and over-excavation.

Estimated volume

0.17cubic yards· 0.13 m³· 4.6 ft³

Bag size	Yield per bag	Bags needed
40 lb	0.3 ft³	16
60 lb	0.45 ft³	11
80 lb	0.6 ft³	8
25 kg	0.413 ft³	12
30 kg	0.496 ft³	10

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

Bag size

Price per bag

Ready-mix price per cubic yard

Bagged

$52.00

8 × 80 lb

Ready-mix

$33.00

0.2 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

How this calculator works

Each post hole is a cylinder — π·(diameter/2)² × depth — and the concrete only fills the space around a set post, so the post's cross-section is subtracted. Enter a post size of 0 to fill the whole hole as a mass footing.

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 post holes sizes, already calculated

Concrete for 6 × 8 in post holes, 24 in deep0.12 yd³6 × 80 lb bags Concrete for 6 × 8 in post holes, 36 in deep0.18 yd³8 × 80 lb bags Concrete for 6 × 10 in post holes, 24 in deep0.2 yd³10 × 80 lb bags Concrete for 8 × 10 in post holes, 30 in deep0.34 yd³16 × 80 lb bags Concrete for 6 × 10 in post holes, 36 in deep0.31 yd³14 × 80 lb bags Concrete for 9 × 12 in post holes, 36 in deep0.7 yd³32 × 80 lb bags Concrete for 9 × 12 in post holes, 42 in deep0.82 yd³37 × 80 lb bags Concrete for 12 × 12 in post holes, 48 in deep1.25 yd³57 × 80 lb bags

Other pours

More calculators

SlabPatios, floors, driveways and pads — length × width × thickness.FootingStrip and spread footings — length × width × depth.ColumnRound columns and sonotube piers — π·r²·height.StepsSolid poured stairs — stacked step cross-sections × width.CurbCurbs and curb-and-gutter — cross-section × run.