How to use it
- Enter post length (ft), width (ft), and thickness (in)
- Click Calculate
- Read cubic yards for supplier orders, bags for DIY, cubic feet as a cross-check
Enter your post dimensions — length, width, and thickness — and this calculator returns the exact concrete volume you need in three useful units: cubic yards for ordering from a supplier, cubic feet for smaller jobs, and bags (based on 0.6 cu ft per 80-lb bag) for DIY purchases.
Knowing the right volume prevents two costly mistakes: ordering too little and facing a mid-pour shortage, or ordering too much and paying for unused material. The result tells you exactly what to buy before you start mixing.
Read cubic yards first if you're sourcing from a ready-mix truck; check bags second if you're buying mix by the pallet; use cubic feet as a cross-check. All three units describe the same volume — pick the one that matches how you buy.
Pro tips
- Add 10% waste allowance for spillage and over-excavation
- Round up bag counts — partial bags aren't sold
- Order 5-10% extra for ready-mix; returns are costly
- Double-check thickness — it's the most commonly mis-measured dimension
Real-life examples
- Setting a 4×4 mailbox post in a rectangular footing
- Pouring a small shed post foundation before weekend
- Replacing rotting fence posts with new concrete footings
Case study
Maria needed 3 fence posts. She measured each hole at 2 ft deep, 1 ft wide, 1 ft long — 2 cu ft per post, 6 total. The calculator showed 0.22 cu yards and 10 bags. She ordered exactly 10 bags, avoided a second trip, and finished in one afternoon.