Concrete Calculator — How Much Concrete Do You Need?
Work out cubic yards, cubic metres, bags of premix and the total cost for slabs, footings, columns and stairs. Enter your dimensions and get a ready-mix and bag quantity you can order from with confidence.
Enter your dimensions above to see the estimate.
Why this concrete calculator beats a plain volume formula
Most concrete calculators stop at cubic yards. That single number is not enough to place an order — you still need a bag count, a waste allowance and a price comparison before you know whether to book a truck or load up on premix. This tool does all four in one screen.
Four pour types, one page
Slabs and walls, strip footings, round columns and sonotubes, and poured stairs — each with the right formula and a labelled diagram, instead of four separate pages.
Imperial and metric that actually convert
Switch units and your entered dimensions convert with you. Feet become metres, inches become centimetres, and the price per cubic yard becomes a price per cubic metre.
Bag counts for every bag size
See how many 40, 50, 60 or 80 lb bags (or 20, 25, 30 and 40 kg bags) the pour needs, rounded up to whole bags the way the store sells them.
Live cost comparison
Enter your local ready-mix price and bag price and the calculator tells you which delivery method is cheaper for this specific pour — the decision most sites leave you to guess.
Waste factor built in
Uneven subgrade, spillage and over-excavation all eat concrete. Pick a 5–20% allowance and the order quantity updates instead of leaving you short mid-pour.
Built for the job site
Large tap targets, no sign-up, no pop-ups and a layout that works one-handed on a phone with gloves on. Results update as you type and can be copied in one tap.
How to use the concrete calculator
Pick what you are pouring
Choose Slab / Wall, Footing, Round Column or Stairs. The input fields and the diagram change to match, so you are never guessing which measurement goes where.
Enter your dimensions
Length and width in feet or metres, thickness and depth in inches or centimetres. Add a quantity if you are pouring several identical slabs, footings or columns.
Set waste, bag size and price
A 10% waste allowance suits most jobs. Choose the bag size you can buy locally and type in your ready-mix and bag prices to get a realistic cost.
Read the order quantity
The headline figure is what to order, waste included. Below it you get exact volume, cubic yards, cubic metres, bag count and the cheaper supply option. Tap Copy results to send it to your supplier.
The formulas behind the numbers
Every result on this page comes from standard volume geometry, then a conversion to the units a supplier actually sells in. There are 27 cubic feet in a cubic yard and 35.315 cubic feet in a cubic metre.
| Pour type | Formula | Worked example |
|---|---|---|
| Slab or wall | Length × Width × Thickness | 10 ft × 10 ft × 4 in = 33.33 ft³ = 1.23 yd³ |
| Strip footing | Length × Width × Depth | 40 ft × 16 in × 12 in = 53.33 ft³ = 1.98 yd³ |
| Round column | π × radius² × Height | 12 in dia × 8 ft = 6.28 ft³ per column |
| Stairs | Width × Run × Rise × n(n+1)/2 | 5 steps, 11 in run, 7.5 in rise, 3.5 ft wide = 30.1 ft³ |
Bag yield and coverage reference
| Bag size | Yield per bag | Bags per cubic yard | Bags per cubic metre |
|---|---|---|---|
| 40 lb | 0.30 ft³ | 90 | 118 |
| 50 lb | 0.375 ft³ | 72 | 95 |
| 60 lb | 0.45 ft³ | 60 | 79 |
| 80 lb | 0.60 ft³ | 45 | 59 |
| 20 kg | 0.0093 m³ | 82 | 108 |
| 30 kg | 0.0139 m³ | 55 | 72 |
Typical slab thickness by application
| Application | Thickness | Coverage of one cubic yard |
|---|---|---|
| Garden path, shed base | 3–4 in (75–100 mm) | 81–108 ft² |
| Patio, sidewalk | 4 in (100 mm) | 81 ft² |
| Residential driveway | 5–6 in (125–150 mm) | 54–65 ft² |
| Garage floor, RV pad | 6 in (150 mm) | 54 ft² |
| Heavy vehicle or shop slab | 8 in (200 mm) | 40 ft² |
What you get from an accurate concrete estimate
- No mid-pour shortfall. Running out of concrete creates a cold joint that permanently weakens the slab, and a second delivery costs more than the concrete itself.
- No wasted overspend. Ordering two extra cubic yards "just in case" is money poured onto the ground, and you still have to dispose of it.
- A clear bags-versus-truck decision. Under roughly one cubic yard, bags usually win. Above two, ready-mix almost always does.
- A realistic budget before you call a supplier, including the waste allowance most quotes assume you already added.
- Correct quantities for reinforcement, formwork and labour planning, because they all scale off the volume.
- A number you can send straight to the batching plant, with units they recognise.
Concrete calculator FAQs
How much concrete do I need for a 10x10 slab?
How many bags of concrete are in a cubic yard?
How do I convert cubic feet of concrete to cubic yards?
How much extra concrete should I order for waste?
Is it cheaper to use bagged concrete or ready-mix?
How much concrete does a 12-inch sonotube need?
How do you calculate concrete for stairs?
How much area does one cubic yard of concrete cover?
Related calculators
Order the right amount of concrete, first time
Measure once, enter the dimensions, add a waste allowance and you have an order quantity, a bag count and a cost you can defend. Scroll back up, switch to the tab that matches your pour and copy the results straight into your supplier request.
Estimates are for planning only. Confirm thickness, reinforcement and mix strength with your local building code or a qualified engineer before pouring structural concrete.