Post hole concrete calculator
Estimate concrete around a round or rectangular post. Subtract the embedded post volume, add allowance and calculate whole bags.
Centred constant-section round or rectangular posts in identical cylindrical holes, up to 10,000 holes. Embedded length cannot exceed fill depth. The estimate must leave positive concrete volume. Whole bags are limited to 1 billion. Change the input or settings to update your result. Results update as you type. Up to 1,000,000 characters.
Your result
How to use Post hole concrete calculator
- Enter the hole diameter and concrete fill depth.
- Set actual post dimensions and the length embedded in concrete.
- Add hole count, allowance and product yield, then download the bag estimate.
Useful next steps
Measure the concrete region
Enter a circular hole diameter and the depth that will actually contain concrete. Exclude gravel, an unfilled top and other voids. This fill depth is a measurement input; the calculator does not determine a required foundation depth.
Subtract the embedded post
Choose a round or rectangular post and use actual measured dimensions. Embedded length means only the length inside the concrete region. It can be shorter than fill depth. For a rectangular post, the cross-section diagonal must fit within the circular hole in this centred geometric model.
Use volume yield per bag
After subtracting the post, the calculator multiplies by the number of identical holes and your allowance. Bag count rounds up using the product's volume yield. Do not enter a bag's weight as its volume. A 300 mm diameter by 900 mm fill around a 100 × 100 mm fully embedded post contains about 54.617 litres before allowance.
Keep the estimate and its assumptions
Download litres, cubic metres, cubic feet, cubic yards and bags in a CSV or report. The geometry does not establish footing depth, frost protection, reinforcement, load capacity or code compliance.