This worked example uses dimensions selected and measured outside the calculator: six round holes, each with 0.30 m outer diameter and 0.80 m depth, containing round posts of 0.10 m diameter. The user chooses a 5% extra and enters a finished yield of 0.012 m³ per bag from the exact label. The scenario demonstrates annular geometry, deterministic π, and whole-bag rounding. It does not recommend hole size, depth, post size, allowance, mix, or construction method.
Subtract the round post cross-section
The outer radius is 0.30/2 = 0.15 m and the post radius is 0.10/2 = 0.05 m. Their squared difference is 0.15² − 0.05² = 0.0225 − 0.0025 = exactly 0.0200 m² before multiplication by π. This subtraction represents only the measured round post occupying the centre. It cannot be reused for a square or irregular post. If no inner object were entered, the second squared term would be zero and the full cylinder cross-section would remain.
Multiply by fixed π, depth, and quantity
ConcreteCalc uses π = 3141592653589793/1000000000000000. One annular hole is π × 0.0200 × 0.80 = 0.050265482457436688 m³. Six equal holes give exactly 0.301592894744620128 m³ under that fixed approximation. At display precision this is 0.301593 m³, or about 301.593 litres. The unrounded rational value, not the six-decimal display, continues into the extra and package calculations. This keeps the arithmetic repeatable across browser and server rendering.
Apply the chosen 5% and round the entered yield
Multiplying the exact base volume by 1.05 gives 0.3166725394818511344 m³, displayed as 0.316673 m³. The added volume is 0.0150796447372310064 m³. With the exact selected label yield entered as 0.012 m³ per bag, division gives about 26.389378 bags, which rounds upward to 27 whole bags. The 5% is the user’s explicit choice; the fraction above 26 comes from division, and the final step comes from whole-package rounding. None of them is a hidden second allowance.