Measure the material footprint

Stretch a line across the finished top of the forms. Measure down to the prepared base near the corners and through the middle. A single deep pocket can take more material than the nominal slab thickness suggests. Split thickened edges and pads into their own measured sections. When adding them to the main pour, count only the depth below the slab so the same concrete is counted once.

Check the approved slab and subgrade details before taking final dimensions. IRC Chapter 5 addresses preparation and compaction of fill beneath a concrete floor. Ask the project team for the specified lift thickness, moisture conditions and acceptance tests for the actual soil. Record the final thickness after preparation. Adding a general waste allowance to a takeoff cannot compensate for an unmeasured edge beam or a change in the elevation of the base.

Work through this estimate

Start with the geometry for 16 × 20 ft at 4 in. The footprint is 16 ft × 20 ft, which gives 320 square feet. Convert the depth to the same unit before multiplying. Dividing 4 inches by twelve gives 0.3333 feet. The footprint times that depth gives 106.67 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 117.33 cubic feet to order. Divide that value by twenty-seven to convert to 4.35 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 15605 pounds. Dividing by two thousand gives 7.8 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 196 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 $842.04 delivered, compared with $1,564.08 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.