Post Hole Concrete Calculator (Fence and Deck Posts)

What this tool does

Each hole needs a cylinder of concrete minus the space the post takes up. A common rule of thumb is a hole about three times the post width and a third to a half of the post's height above ground in depth, deeper in loose soil or windy spots — but follow the post or fence maker's guidance. Bags of ready-mix say on the label how much concrete they make; it varies a lot between products, so enter the figure from your bag and buy one or two spare.

Formula

V = n × (π r² − post area) × depth · bags = ⌈V ÷ yield per bag⌉

Variables

Worked example

Limitations

• Always order a little more material than the calculated quantity. Cuts, breakage and pattern matching create waste that depends on the shape of the job.
• Coverage and consumption figures vary between products. Take the values from the manufacturer's datasheet for the product you are actually using.