How the calculations work
Every estimate starts with measured geometry. We keep exact volume separate from a waste-adjusted order and show the assumptions behind bag and cost estimates.
Quick formulas
Rectangular pour: length × width × depth. Round pour: π × (diameter ÷ 2)² × height. Multiply each shape by its quantity, then sum the unrounded volumes. Order volume: exact volume × (1 + waste ÷ 100). Bags: round up (order volume ÷ finished-concrete yield per bag).
Units and rounding
1 yd³ = 27 ft³. 1 ft = 0.3048 m; 1 in = 0.0254 m. Display values are rounded to two decimals, but bag count is calculated from the unrounded volume and then rounded up. Switching units in the main calculator preserves dimensions to four decimal places, which may introduce a very small conversion difference.
Bag-yield sources
US bag yields in the calculators follow the QUIKRETE Concrete Mix data sheet: 40 lb ≈ 0.30 ft³, 60 lb ≈ 0.45 ft³ and 80 lb ≈ 0.60 ft³. The main calculator’s metric 25 kg estimate assumes 0.0125 m³ per bag; actual metric products vary. The main and bag calculators let you replace that assumed yield with the finished-concrete yield on your chosen product label.
Post hole subtraction
The post hole calculator estimates a round concrete-filled hole and subtracts the volume occupied by a square post over the same fill depth. Enter the actual post width. The post must fit within the round hole; the tool checks its corner-to-corner width.
Price comparison
On the main calculator, ready-mix material cost is the suggested supplier-increment order quantity multiplied by your entered price per cubic yard or cubic meter. The suggested order rounds the waste-adjusted volume up to the increment you enter; it does not apply a supplier minimum. Bag material cost is the rounded-up bag count multiplied by the entered price per bag. The displayed difference compares materials only. Delivery minimums, short-load charges, mixing time, labor, taxes and other fees can reverse that difference.
Additional planning tools
The sonotube and round slab tools use cylinder volume. The solid stairs tool sums a stepped cross-section. The gravel base tool uses compacted rectangular volume and only converts to weight if you supply a bulk density. The rebar grid tool counts straight lines at a maximum entered spacing; it does not design steel or optimize cuts. The cost tool uses only your entered price and fees.
Limits of an estimate
These tools estimate quantities, not structural capacity or a safe mix design. The main calculator shows material-only prices. The dedicated cost calculator adds delivery, pump, labor and tax only when you enter those values; none of these fields is a live local quote. Check all amounts against your supplier and project plans.
How this site is maintained
pourmeasure is a free planning tool. Formulas and assumptions are visible so visitors can check the results independently. Formulas and sources are updated when an error is confirmed. Report a calculation or source issue with the page URL, inputs and expected result.