Plan concrete bags for post holes
A reliable post-hole concrete bag purchasing order begins with a sketch and a written measurement worksheet. The linked calculator translates round hole diameter and filled depth, actual rectangular post width and depth, embedded length, number of identical holes, bag weight, and a waste allowance into a quantity estimate. Use the example below to check the method, then enter measurements from your own project. Keep the product choice and source date beside the numbers.
Start with the physical job
Measure the inside diameter and filled depth of each hole, plus the actual size and embedded length of the post. The post embedment cannot exceed the concrete-filled depth and its rectangular diagonal must fit inside the round hole. Non-round holes, tapered excavation, bell footings, gravel bases, and above-grade forms need separate volume treatment. Mark repeated sections explicitly. Note any planned changes before counting materials.
Enter the model inputs
For this worksheet, provide round hole diameter and filled depth, actual rectangular post width and depth, embedded length, number of identical holes, bag weight, and a waste allowance. Read each unit label before entering a value. US customary and metric entry modes describe the same physical job, so check converted values after changing modes. Do not use a product trade name in place of an actual measured dimension unless that is the intended billing convention.
Work the formula by hand
Net cubic feet per hole = [π × (diameter ÷ 2)² × depth − post width × post depth × embedded length] ÷ 1728; apply hole count and allowance, then divide by bag yield and round up. A 12 in by 24 in cylinder is π × 6² × 24 = about 2,714 cubic inches. A 3.5 × 3.5 in post embedded 24 in occupies 294 cubic inches. Net per hole is about 1.401 ft³, four holes about 5.603 ft³, and 10% extra about 6.163 ft³. Dividing by 0.60 ft³ per 80 lb bag and rounding upward gives 11 bags. The example is a transparent arithmetic check, not a universal job specification.
Check the first estimate
Check hole depth after any gravel base and verify which portion is actually filled with concrete. Measure the real post size; a nominal 4×4 is often smaller than four inches. Recalculate after fixing any mismatch. Keep the unchanged source measurement on the sketch, so an entry error is distinguishable from a real project revision.
Plan the material purchase
Confirm that the store stocks the selected weight of QUIKRETE 1101 and compare its current yield with the data sheet. Keep a little practical handling margin but do not substitute a slab-volume estimate for the hole geometry. Ask the seller for the current product information before checkout. Save the exact package or stock description used when checking the estimate.
Know the limits
The yield table belongs specifically to QUIKRETE Concrete Mix No. 1101: 40 lb 0.30 ft³, 50 lb 0.375 ft³, 60 lb 0.45 ft³, and 80 lb 0.60 ft³, approximately. Other mixes or labels require their own yield. A material calculator cannot verify field conditions or authorize construction. Confirm any design-dependent value in the plan or with the responsible professional.
Keep a traceable worksheet
A useful order begins with a dated sketch, a product name, and dimensions recorded in their original units. Mark each repeated element so that its count can be checked against the site. Record where each figure came from: a tape measure, a plan, a supplier listing, or a design detail. This makes later changes auditable. If two sections differ, estimate them separately before adding the purchase quantities. A single average may hide a small but important difference at a boundary.
Read the result in stages
The calculator shows intermediate quantities so the final purchase count can be checked. Work through the displayed values in order instead of treating the last number as a guarantee. Keep full precision during the calculation and round only where the model says a purchasable whole item is required. A value just over a whole item still requires another item. If the answer changes after switching units, check whether converted entries were rounded in the form or whether a product-specific unit was assumed.
Separate quantity from design
This worksheet estimates material amounts from chosen project inputs. It cannot inspect the site or decide what assembly is safe and suitable. Structural requirements, local rules, product instructions, drainage, loads, and installation methods belong in the project design. Resolve those matters before treating a material estimate as a purchase list. If the design changes, update the dimensions and parameters and calculate again. Do not use an arbitrary extra percentage to repair an incorrect geometry or unsuitable specification.
Check the seller before paying
Compare the measured result with the unit in which the seller actually quotes and sells material. Check available stock sizes, package quantities, delivery constraints, return terms, and whether a listed size is nominal or actual. A quantity that is mathematically correct can still produce a wrong order when a product is sold by a different unit. Save the product page or label used for the estimate. If the listed yield, dimension, or unit price changes, revise the worksheet rather than reusing an old purchase count.
Measure before entering values
Use a second pass to verify the site measurements. Note where an obstacle, slope, existing structure, or changed elevation affects the usable dimension. Keep original measurements and converted values side by side, and do not round a converted dimension early. When separate sections use different products or layouts, make a worksheet for each. This prevents a valid total for one section from being wrongly applied to the rest of the job.
Understand the purchase rounding
The geometric requirement and the purchasable item count answer different questions. Geometry may yield a decimal volume or length. Stock bars, boards, studs, and concrete bags are bought as whole units, so a ceiling is applied at the purchase step. Do not round down because the decimal appears close to an integer. Conversely, examine whether a large surplus is caused by package size, layout boundaries, or an incorrect input before adding more.
Make a separate installation list
The material count does not automatically include fasteners, anchors, forms, ties, tools, delivery, protective equipment, or labor. Write those on a separate job list where relevant. Check access to the work area and confirm that the chosen stock can be carried, stored, cut, mixed, or placed as planned. Site constraints may influence what size package is practical even when two products have the same calculated material coverage.
Review a changed plan
If the project changes, circle the changed dimension or assumption on the sketch and rerun the calculation. Compare the old and new intermediate values, not only the final order. A small change near a spacing interval or package boundary can add a whole item. Keep a short note of why a value changed so the revised order remains understandable after measurements, product choice, or design details are updated.
Open the Post Hole Concrete Bag Calculator to enter your dimensions and keep the resulting purchase count with this worksheet.