Post Hole Concrete Calculator

Setting fence posts or deck footings goes a lot smoother when you know how many bags of concrete the holes will swallow before you head to the store. Estimating the count accurately means you don't haul home a pallet of leftovers or stall the job halfway through for a second trip.

Because a post hole is essentially a cylinder, the volume comes from V = π * (r^2) * h, where r is the radius (half the hole's diameter) and h is the depth. The calculator works in feet and divides each hole's volume by 0.60 cubic feet, the yield Quikrete gives for an 80 lb bag of its Concrete Mix (its 60 lb bag yields about 0.45 cubic feet and its 50 lb bag of Fast-Setting Concrete Mix about 0.375). It rounds up to a whole bag per hole, so you're never left a scoop short, and multiplies by the number of holes. It fills the whole hole with concrete and does not subtract the post or a gravel base.

Rounding up is deliberate, since holes are rarely perfectly straight, some mix is always lost to spillage, and yields drift a little from bag to bag. Those yields also shift by manufacturer and mix type, so it pays to read the figure printed on the bag you actually buy. The error that bites most often is shorting the depth, which leaves you with too little concrete and a footing that won't hold the post the way it should.