Quick navigation: Measurements · Materials & Mix · Costs & Ordering · Pour & Logistics
Measurements & Formulas
How do I calculate concrete for a rectangular slab?
Volume (ft³) = Length (ft) × Width (ft) × Thickness (in) ÷ 12. To convert to cubic yards divide ft³ by 27. Add a waste factor (10% normal, 15% complex).
How do I calculate for a circular slab or column?
Circular area = π × radius². Volume = area × thickness. For columns use height × area. Convert units as needed (inches → feet).
What if I have an irregular shape?
Break the area into rectangles/triangles/circles, calculate each separately, then sum volumes. The calculator also supports many project types to simplify this.
Worked example — patio (20×12, 4")
20 × 12 × (4 ÷ 12) = 80 ft³ → 80 ÷ 27 = 2.96 yd³ → +10% waste → 3.26 yd³.
Materials, Mixes & Quantities
How many 80 lb bags per cubic yard?
About 45 bags of 80 lb concrete mix per cubic yard (approximate — bagged mixes vary).
What mix ratio is used?
Standard mixes use a 1:2:3 ratio (cement : sand : gravel). The calculator uses reasonable defaults and provides advanced mix adjustments when you enable Professional mode.
Do I need reinforcement (rebar/mesh/fiber)?
Small slabs often use wire mesh; driveways and structural elements commonly need rebar. Use Advanced Mode to include reinforcement estimates and cost impact.
Costs, Pricing & Exporting
How much does concrete cost per cubic yard?
Prices vary widely by region and mix strength; the calculator shows regional comparisons in the Costs tab after a calculation. You can edit cement price and labor in Advanced to match local quotes.
Can I export a PDF or share results?
Yes — Export as PDF creates a professional report; Copy All Results copies a summary to clipboard. Save projects locally for later comparison.
Pouring, Scheduling & Practical Tips
How many trucks do I need?
Most ready-mix trucks hold ~8–10 yd³. For larger pours plan multiple trucks and staging; the dynamic tips show truck estimates for your job size.
When should I schedule delivery?
Order 2–3 days ahead and prefer morning deliveries in hot weather. Coordinate site prep, crew, and access before the truck arrives.
How long do I have to place concrete?
Ready-mix concrete should typically be placed within 90 minutes of mixing; hot weather shortens this window. For big pours, plan logistics and pumping as needed.
Quick troubleshooting
- If a field is disabled and required, re-enable it or follow the on-screen warning to avoid inaccurate estimates.
- Use metric mode only if your inputs are in meters/cm; mismatched units will skew results.
- If charts or 3D view look off, refresh the page or recalculate to re-render visuals.