{"id":"concrete-post-hole-calculator","name":"Post Hole Concrete Calculator","shortName":"Post Hole Concrete","canonicalUrl":"https://calcurhome.com/calculators/concrete-post-hole-calculator","catalogUrl":"https://calcurhome.com/api/calculators","category":{"id":"concrete-masonry","name":"Concrete & masonry","url":"https://calcurhome.com/calculators/category/concrete-masonry"},"language":"en-US","audience":"US homeowners, DIYers and home-project planners","primaryKeyword":"post hole concrete calculator","secondaryKeywords":["concrete post hole calculator","fence post concrete calculator","concrete for round holes","post hole bag calculator","deck post concrete calculator"],"description":"Calculate concrete volume and 80-pound bag count for round post holes from diameter, depth, post displacement, hole count, and placement waste.","directAnswer":"Find each hole’s cylindrical volume, subtract the embedded round-post volume, multiply by the hole count, and add placement waste. This page owns post-hole concrete and bag quantity; use the Fence Post Spacing Calculator first when the unresolved task is post count or layout.","inputs":[{"key":"holeDiameter","label":"Hole diameter","unit":"in","defaultValue":12,"min":1,"step":0.5},{"key":"holeDepth","label":"Hole depth","unit":"ft","defaultValue":3,"min":0.1,"step":0.1},{"key":"postDiameter","label":"Round post diameter","unit":"in","defaultValue":4,"min":0,"step":0.25},{"key":"holes","label":"Number of holes","unit":"holes","defaultValue":8,"min":1,"step":1},{"key":"waste","label":"Placement allowance","unit":"%","defaultValue":10,"min":0,"max":30,"step":1}],"formula":{"title":"Concrete around round posts","expression":"Concrete = π × [(hole radius)² − (post radius)²] × depth × holes × waste factor","explanation":"The formula subtracts a round post cylinder from each round hole cylinder. Dimensions are converted to feet before volume is calculated, so the result is cubic feet and can then be converted to bags or yards."},"measurementGuide":["Measure hole diameter across the widest point and depth from finished grade to the bottom.","Check several holes because augers and loose soil rarely produce identical cylinders.","Enter the embedded diameter of a round post, or zero to ignore displacement.","Calculate bell-shaped bases, footings, or rectangular posts separately for a closer estimate."],"buyingTips":["Call the required utility-location service before digging and respect marked exclusion zones.","Confirm post depth, diameter, frost, drainage, uplift, and inspection rules locally.","Keep bagged mix dry and compare total mixing effort with a small ready-mix delivery.","Brace posts before placement and follow the concrete and post manufacturers’ curing guidance."],"workedExample":{"title":"Eight fence posts","scenario":"Eight 12-inch-diameter holes are 3 ft deep around 4-inch round posts, with 10% extra.","result":"Net volume is 16.76 cu ft; with extra it is 18.43 cu ft, or about 31 80-lb bags."},"commonQuestions":[{"question":"How many bags of concrete do I need per fence post?","answer":"A 12-inch-diameter, 3-foot-deep cylindrical hole around a 4-inch round post uses about 2.10 cubic feet before waste, or roughly four 80-pound bags at 0.60 cubic foot each. Actual irregular holes may use more."},{"question":"Should I subtract the fence post from the hole volume?","answer":"Yes, for a tighter material estimate, subtract the embedded post volume. The difference is most noticeable with large posts or many holes. For irregular or rectangular posts, the calculator’s round-post assumption is approximate, so retain a practical allowance."},{"question":"How deep should a post hole be?","answer":"Depth depends on fence or deck loads, post height, soil, frost depth, wind, uplift, and local code. Do not choose depth from a concrete estimate. Follow approved plans, manufacturer instructions, and requirements from the local building authority."},{"question":"Can I pour dry concrete mix into a post hole?","answer":"Only use a dry-placement method if the specific manufacturer expressly permits it and follow its water and installation directions. Conventional mixing generally provides better control. Structural posts need the specified concrete quality, consolidation, positioning, and curing."}],"sources":[{"name":"QUIKRETE Concrete Mix Product Data","url":"https://www.quikrete.com/pdfs/data_sheet-concrete%20mix%201101.pdf","note":"Manufacturer product data used to cross-check typical bag yields; verify the yield printed on the bag you buy."},{"name":"International Code Council — 2024 International Residential Code","url":"https://codes.iccsafe.org/content/IRC2024P1","note":"Primary model-code source for residential foundations, reinforcement, masonry, and stair safety requirements."}],"defaultCalculation":{"inputs":{"holeDiameter":12,"holeDepth":3,"postDiameter":4,"holes":8,"waste":10},"result":{"value":"31","unit":"80-lb bags","label":"Approximate concrete bags","lines":[{"label":"Concrete volume","value":"18.43 cu ft"},{"label":"Concrete in cubic yards","value":"0.68 cu yd"},{"label":"Net volume per hole","value":"2.09 cu ft"},{"label":"Equal holes","value":"8"}],"summary":"The 8 holes require about 18.43 cubic feet of concrete after allowance.","note":"Bag count assumes 0.60 cubic foot per 80-pound bag. Posts are modeled as round; use zero post diameter when you do not want displacement deducted."}},"reviewedOn":"2026-07-23","disclaimer":"Planning estimate only. Verify product coverage, supplier rounding, local codes and structural requirements before purchase or construction."}