Concrete Calculator
Estimate concrete volume, bags, ready-mix yards, and total cost for slabs, columns, footings, and stairs — all in one pour list.
Pours
Typical: 5–10% for slabs and footings. Add more for awkward forms or spillage.
Tick "Include" to estimate the number of pre-mix bags or ready-mix yards plus total cost.
Your estimate
About Concrete Calculator
The Concrete Calculator estimates the volume of concrete you need for any DIY or contracting pour — from a small patio slab to a deep footing, a round Sonotube column, or a flight of stairs. Enter each pour, pick its shape, and the calculator sums everything to a clean total in cubic feet, cubic yards, or cubic meters.
Optionally toggle on a cost estimate: choose pre-mix bags (40 / 50 / 60 / 80 / 90 lb) and your local price per bag, or ready-mix delivery and price per yard (or per m³). The bag count rounds up so you never come up short on pour day.
How to Use Concrete Calculator
- 1 Pick your unit. Toggle Imperial (feet + inches) or Metric (meters + centimetres) at the top of the Pours card.
- 2 Pick a shape per pour. Choose Slab/Rectangle, Column (round), Footing/Wall, or Stairs. The input fields change to match the shape.
- 3 Enter the dimensions. Length and width use the larger unit (ft or m). Thickness, depth, diameter, rise, and run use the smaller unit (in or cm) because they're usually small numbers.
- 4 Add more pours. Click "Add another pour" for additional shapes — footings around a slab, stairs leading up to it, columns for a porch. The estimate sums everything.
- 5 Set waste %. 10% is a sensible default. Add more for forms that are likely to spill or for hand-mixed jobs where small over-batching is normal.
- 6 (Optional) Cost it. Tick "Include", then switch between Bags and Ready-mix. Bag mode asks for the bag size and price; ready-mix mode asks for price per yard or m³.
Frequently Asked Questions
How thick should my concrete slab be? ▾
Common thicknesses: 4 inches (10 cm) for patios, walkways, and shed pads; 5–6 inches (12–15 cm) for driveways and floors that carry vehicles; 6–8 inches (15–20 cm) for heavy-duty surfaces. Local codes may require more, especially in freeze-thaw zones — always check before pouring.
How much does a bag of concrete cover? ▾
Approximate yield by bag size (mixed):
- 40 lb bag ≈ 0.30 ft³ (8.5 L)
- 50 lb bag ≈ 0.375 ft³ (10.6 L)
- 60 lb bag ≈ 0.45 ft³ (12.7 L)
- 80 lb bag ≈ 0.60 ft³ (17.0 L)
- 90 lb bag ≈ 0.675 ft³ (19.1 L)
So one cubic yard (27 ft³) takes about 60× 40 lb, 45× 60 lb, or 45× 80 lb bags after rounding.
When should I order ready-mix instead of bags? ▾
Above roughly 1 cubic yard (≈ 0.75 m³), ready-mix is almost always cheaper and easier than bags — that's around 60 × 80 lb bags. Truck delivery also gives you better mix consistency. Below 1 yard, bags are usually faster to source and let you pour at your own pace. Many ready-mix suppliers have a minimum order and "short load" fees, so check pricing first.
How are stairs calculated? ▾
Stairs are modelled as a "staircase volume" — each step is a stacked rectangle of width × run × cumulative rise. The formula is Volume = width × rise × run × n(n+1)/2, where n is the number of steps. This assumes solid stairs poured against a back wall or hillside; for open or freestanding stairs you'll need slightly more for the side walls.
What waste percentage should I use? ▾
10% is a safe default. Use 5% if the forms are clean, level, and you're an experienced finisher. Use 15% or more for hand-mixed pours where small over-batching is normal, or when the subgrade has dips that the concrete will fill. Better to have a wheelbarrow of spare than a cold joint mid-pour.
Does this work for round columns and Sonotubes? ▾
Yes — pick the "Column (round)" shape and enter the inside diameter of the form (8", 10", 12" are common Sonotube sizes) plus the height. The calculator uses π r² h for the volume.
Is my data saved or sent anywhere? ▾
No. Everything runs in your browser. Your dimensions and prices never leave your device and nothing is stored on a server.