Concrete Slab Volume
Slab volume from length, width, and thickness — plus bag counts and a waste allowance.
Your recent runs (stored only in your browser)
No calculations yet — results land here so you can compare runs.
The engineering
Plain box arithmetic, with the two numbers a real pour needs: cubic yards, because that is how ready-mix trucks are ordered in the US, and bag counts for small jobs. Bag yields used here are the manufacturer's typical figures — 0.017 m³ (about 0.45 ft³) from a 60-lb bag and 0.022 m³ (about 0.60 ft³) from an 80-lb bag of pre-blended concrete mix.
The bag counts already include the 10% waste allowance, which covers subgrade irregularity, spillage, and the universal truth that forms are never quite the size of the drawing. For slabs on uneven ground, measure thickness at several points and use the worst case — under-ordering concrete mid-pour is a cold-joint generator.
Where this math comes from
Concrete is Roman — the Pantheon's dome still stands on pozzolana cement — but the modern material starts with John Smeaton, who in 1756 systematically tested limes to find one that would set underwater for the Eddystone Lighthouse and identified the clay content as the key. Joseph Aspdin patented 'Portland cement' in 1824, named for the limestone it resembled, and his son William quietly made it actually work by over-burning the kiln.
The cubic-yard economy arrived when concrete became a delivered product: the first ready-mixed concrete was delivered in Baltimore in 1913, and by mid-century the transit mixer had made 'how many yards?' the first question of every pour.
- 1756John SmeatonHydraulic lime identified for the Eddystone Lighthouse — modern concrete's starting gun.
- 1824Joseph AspdinPatents Portland cement.
- 1913Baltimore ready-mix pioneersFirst ready-mixed concrete delivered — the cubic yard becomes a commodity.
See the full timeline of the math behind every calculator →
Runs entirely in your browser — nothing you enter leaves this page. Your recent runs are stored only on your device.