Measure the material footprint

Measure the inside diameter of the form and the full height of concrete inside it, including any tube above finished grade. A widened base has a different cross section. Sketch that base and calculate its volume separately, ending the straight cylinder where the enlargement begins. If several holes differ in depth, calculate each type separately. Add their unrounded volumes before converting to whole bags.

Use dimensions from the approved footing detail. The IRC foundation provisions tie footing support to soil conditions, and local frost criteria affect the detail. A diameter calculated from a material quantity gives no information about allowable load or bearing capacity. Before setting tubes, confirm the required bearing surface, excavation depth and inspection sequence with the local authority. Recheck the pour height after the forms have been braced.

Work through this estimate

Start with the geometry for 18 in diameter × 60 in deep. The footprint is π × (1.5 ft ÷ 2)², which gives 1.77 square feet. Convert the depth to the same unit before multiplying. Dividing 60 inches by twelve gives 5 feet. The footprint times that depth gives 8.84 cubic feet in place. Keep the full precision on the worksheet and round only the displayed result. For a tapered section, measure enough cross sections to represent the change in area.

The current worksheet adds 10% for handling and variation. Multiplying the measured volume by 1.1 produces 9.72 cubic feet to order. Divide that value by twenty-seven to convert to 0.36 cubic yards. A yard is three feet in each direction, which accounts for all twenty-seven cubic feet. If your supplier quotes a different order increment, round the final combined project quantity up to the next increment it actually sells.

For weight, the model uses 3591 pounds per cubic yard. Applying that density to the order gives 1293 pounds. Dividing by two thousand gives 0.65 US short tons. Treat weight as a planning estimate. Moisture, source material and packing affect actual loads. Obtain the supplier’s density before using a takeoff to plan hauling, and use the carrier’s verified payload limits when arranging delivery.

Compare the purchase units

One 80 lb bag covers 0.6 cubic feet under this model. Dividing the unrounded order volume by the bag yield and rounding upward gives 17 bags. Look at the measured yield on the product label when changing brands. A bag’s weight and the volume it contributes to the finished job describe different quantities. If the store stocks multiple sizes, each row is a complete alternative for the same job. Choose one size or prepare a separate mixed-size order.

The bulk allowance uses $165.00 per cubic yard and a delivery fee of $125.00. For this worksheet that gives $184.40 delivered, compared with $135.66 for the least expensive bag option. Get an itemized local quote covering minimum loads, delivery distance, tax and placement. Include any equipment or extra trips in your own comparison. A small change in the delivery charge can reverse the result on a modest job.