How to Calculate Concrete Pour Volume
Accurate concrete estimation prevents the two most expensive pour-day mistakes: running short mid-pour (leading to cold joints and structural weakness) and massively over-ordering (concrete cannot be returned). A few minutes of calculation before calling the batch plant saves real money.
The Formula
Net volume (m³) = area (m²) × thickness (m). Total order volume = net × (1 + waste%). Ready-mix trucks = ceiling(total ÷ 6 m³). Always round up truck count — a partial load still costs the minimum delivery charge, and running short is far more disruptive than a small surplus.
Waste Factor Guidelines
Flat slab on ground: 5%. Elevated slab or footings: 7%. Stairs, curved walls, complex shapes: 10%. Very small pours (< 2 m³): 10–15% because pump residuals become significant. When in doubt, add one extra 5% buffer — it costs far less than a re-pour.
Ordering Tips
Order concrete at least 48 hours in advance. Specify: mix design (strength in psi or MPa), slump (flowability), maximum aggregate size, and admixtures (air entrainment, accelerator/retarder). Confirm delivery time — most concrete has a 90-minute working window from batching.
Frequently Asked Questions
Ready-mix concrete cannot be returned. Pre-designate a spot for excess — a small footing, path repair, or disposal slab. Brief the crew before the pour so no one adds water to slow setting time (adding water reduces strength significantly).
If the truck cannot reach the pour area directly, a boom pump is needed. Add 0.5–1 m³ of pump residuals to your waste factor. Pump trucks typically add $800–1,500 to the total cost and must be booked separately in advance.
Standard concrete reaches about 70% of design strength in 7 days and 100% (28-day strength) in 28 days. Light foot traffic is possible after 24 hours. Do not load the slab with heavy equipment for at least 7 days. Cold weather (below 40°F / 5°C) significantly slows curing.