Calculate the cylindrical volume occupied by concrete, subtract post displacement only when you intentionally model it, multiply by the number of holes, add a visible waste allowance, and divide by the yield printed for the exact bag being purchased. Round only the final bag count up to a whole bag.
Use the concrete-for-posts calculator for circular holes with optional gravel and round or rectangular post displacement. It estimates material volume; it does not select hole diameter, embedment, footing depth, or concrete product.
Plan for variation
- Obtain hole and embedment requirements from the project design, local requirements, and selected product instructions.
- Measure finished hole diameter at representative locations.
- Record total hole depth and any gravel-base depth separately.
- Decide whether post displacement should be included.
- Read yield per bag from the current product label or technical data sheet.
- Choose a waste allowance that reflects excavation shape and site handling.
- Calculate all holes, then round the final purchase count up.
Worked example: four cylindrical holes
Assume four 10-inch-diameter holes with 30 inches of concrete depth, no modeled post displacement, and a 60-pound product whose current data sheet states approximately 0.45 cubic foot of yield per bag.
One hole contains:
pi x 5 inches x 5 inches x 30 inches = about 2,356 cubic inches, or about 1.36 cubic feet.
Four holes require about 5.45 cubic feet before waste. With a user-selected 10 percent waste allowance, the planning volume becomes about 6.00 cubic feet. Dividing by 0.45 cubic foot per bag gives 13.33, so the purchase estimate rounds up to 14 bags.
Changing product yield changes the bag count even when geometry stays the same. Enter the label value rather than relying on the example.
Input checklist
- Whole number of holes.
- Finished hole diameter.
- Total hole depth.
- Gravel depth, if any.
- Concrete depth: total depth minus gravel depth.
- Post shape and dimensions, only if displacement is included.
- Yield per bag from the selected product.
- User-selected waste percentage.
- Price per bag only after quantity assumptions are settled.
Common mistakes
- Using total hole depth as concrete depth while also adding a gravel base.
- Using post diameter instead of hole diameter.
- Treating a hand-dug tapered hole as a perfect cylinder without allowance.
- Copying yield from a different bag size or product.
- Rounding each hole independently when bags can be shared across the project.
- Subtracting the full post volume when concrete occupies only part of the hole.
- Assuming the material estimate approves footing dimensions or installation.
The measurement guide shows how to enter hole and post dimensions in US customary or metric notation without changing the calculator's canonical geometry.
Limits and sources
The QUIKRETE Fast-Setting Concrete Mix data sheet is a manufacturer example: it lists approximate yields of 0.375 cubic foot for its 50-pound bag and 0.45 cubic foot for its 60-pound bag. Those values are not universal and may change, so check the product being purchased. Exact unit conversions use the NIST SP 811 conversion factors. The concrete methodology documents MaterialNest's volume, displacement, waste, and rounding sequence.
Soil capacity, frost depth, wind exposure, post loading, drainage, hole geometry, and local rules are outside this estimate. Have critical footing and structural decisions reviewed by an appropriate qualified professional.
Reviewed: July 29, 2026. Sources were checked on that date. Send product-yield or formula corrections to feedback@materialnest.com.