Concrete Calculator: Volume, Materials & Mixer Payback

How the concrete volume is calculated

For a slab, footing, strip foundation or wall the volume is simply length × width × thickness. For a round column it is π × radius² × height. The result is multiplied by the number of identical elements and then by the waste allowance — 5 % is normal for slabs poured on a good sub-base; use 8–10 % for uneven ground, footings dug by hand or small scattered pours.

Enter thickness in centimetres (or inches) and plan dimensions in metres (or feet); the calculator converts everything to cubic metres and cubic yards (1 yd³ = 0.7646 m³).

Where the material quantities come from

Cement, sand, gravel and water are worked out from a typical nominal mix for each strength class, per cubic metre of finished concrete:

• C20/25 — about 300 kg cement, 780 kg sand, 1,150 kg gravel, 180 L water
• C25/30 — about 340 kg cement, 740 kg sand, 1,150 kg gravel, 180 L water
• C30/37 — about 380 kg cement, 700 kg sand, 1,130 kg gravel, 175 L water

Treat these as ordering estimates. Real mixes vary with aggregate size, moisture and admixtures, and a structural pour should always follow the mix design your engineer specifies. A self-loading mixer weighs every batch electronically, which is what makes a written mix design repeatable on site.

Working from a different grade system — M25, B25, f’c 250 kg/cm² or 3,500 psi? Look it up in the concrete grade conversion chart.

How the payback is calculated

The second tab compares a self-loading concrete mixer with what you use today:

• Against ready-mix: your cost per m³ becomes materials + fuel + one operator + maintenance, spread over the concrete you produce in a year. The saving is the difference from the delivered ready-mix price.
• Against a small drum mixer and crew: materials are bought either way, so only labour and running costs are compared — the whole crew’s wages against one operator plus fuel and maintenance.

Payback (months) = machine price ÷ net annual saving × 12. Machine prices are our published FOB starting prices; add freight and import duty for your country for a landed figure. The reasoning behind the labour side is explained in how a self-loading mixer replaces 4–6 workers.