This worked example demonstrates the calculator’s arithmetic; it does not recommend a slab thickness, allowance, mix, or package. The user has already chosen a rectangular pour 10 ft long, 10 ft wide, and 4 in thick, quantity one. The user deliberately enters 8% extra and copies a finished yield of 0.60 ft³ per bag from the exact product being considered. Keeping those choices explicit makes the base volume, added volume, adjusted volume, and bag rounding independently reviewable.
Normalize thickness and calculate base volume
Four inches equals exactly 4/12 foot, or 1/3 foot. The rectangular formula is 10 ft × 10 ft × 1/3 ft × 1 = 100/3 ft³, which is 33.333… ft³. Dividing by 27 gives 100/81 yd³, approximately 1.234568 yd³. The repeated decimal is not truncated inside the calculation: ConcreteCalc keeps the rational fraction and rounds only the displayed conversion. The base result contains no extra percentage and no package rounding.
Apply the selected 8% as a separate stage
The explicit extra volume is 100/3 × 8/100 = 8/3 ft³, or 2.666… ft³. Adding it to the base gives 108/3 = exactly 36 ft³, equivalent to 4/3 yd³ or approximately 1.333333 yd³. The 8% belongs to this worked scenario because the user entered it; ConcreteCalc does not present it as typical or suitable for another project. Leaving the field at zero would keep the adjusted result equal to the base volume.
Use the entered label yield for whole bags
The selected package states a finished yield of 0.60 ft³ per bag. Dividing the exact adjusted volume gives 36 ÷ 0.60 = 60, so the result is 60 whole bags with no further rounding in this case. A different label yield would produce a different count even if its bag mass looked similar. If the user enters a matching bag price, optional cost is 60 multiplied by that price. Tax, delivery, stock, labour, site loss, and product suitability remain outside the example and must not be inferred from the result.