Concrete Calculator
Enter a few dimensions. We'll calculate the rest.
Getting your concrete order right
Measure the full pour area, account for subgrade, and always round up — running short mid-pour costs far more than a leftover bag.
Pouring round footings and sonotubes
Cardboard tube forms — commonly known by the Sonotube brand name — are the standard way to pour deck footings, posts and pier foundations. Volume depends on tube diameter and pour depth, and it’s easy to underestimate: a 12-inch tube poured 4 feet deep takes just over 3 cubic feet of concrete. Select Round Footing above and enter your diameter and depth.
Setting fence posts instead of pouring a slab? The fence post concrete calculator works out post-hole volume and post spacing together.
What a concrete pour actually costs
Concrete pricing varies too much by region, supplier and mix for a single national figure to be useful, so we don’t publish one. We’re validating cost assumptions with working contractors before adding cost estimates to the calculator — we’d rather give you a quantity you can trust than a price you can’t.
What is consistent is the shape of the decision. Bagged mix is usually cheaper for small pours. Ready-mix delivery gets cheaper per yard as volume rises, but most suppliers charge a short-load fee below roughly 8–10 cubic yards, which can wipe out the saving entirely on a small job. Somewhere between one and three cubic yards, delivery typically overtakes bags — but where exactly depends on your supplier’s fee structure.
Three things that move the number: the mix you specify (higher-strength and fibre-reinforced mixes cost more), how far you are from the plant, and whether the pour needs a pump rather than a chute.
Get your quantity from the calculator above, then price it two ways: bags at your local yard, and a delivered quote including any short-load fee. At small volumes the cheaper option is less obvious than it looks.
Laying a gravel sub-base under the slab?
Most slabs sit on a compacted gravel sub-base rather than straight on soil. The gravel calculator gives you tonnage by gravel type, and allows for the depth crusher run loses once it is rolled.
Related calculators
- gravel calculator — for the sub-base under the pour.
- tile calculator — for tiling the slab once it has cured.
- drywall calculator — for finishing the walls around it.
- rebar calculator — bar counts, spacing and lap splices for your pour.
- insulation calculator — basement and slab-edge insulation
- Lumber Calculator — formwork and framing material
- Stair Calculator — for poured steps and landings
FAQFrequently asked questions
About 90 bags of 60 lb mix, or 60 bags at 80 lb — that’s a 4-inch pour, roughly 1.24 cubic yards including a 10% waste allowance. Enter your exact dimensions above for a precise count.
4 inches is standard for walkways, patios, and shed pads. Driveways and anything carrying vehicle weight should be 5–6 inches, typically reinforced with rebar or wire mesh.
5–10% covers typical spillage and subgrade variation. Use 10–15% for irregular shapes, hand-mixed pours, or a subgrade that isn’t perfectly level.
A 4-foot pour needs roughly 1.6 cubic feet for an 8-inch tube, 3.1 for a 12-inch, and 7.0 for an 18-inch. Use the Round Footing shape above for exact figures at your diameter and depth, including bag counts.
About 45 bags of 80 lb mix, 60 bags at 60 lb, or 90 bags at 40 lb. These are approximate — yield varies slightly by mix and how wet you mix it.
Yes — the cubic yard (or cubic meter) figure is exactly what a ready-mix supplier will quote from. Most suppliers have a delivery minimum, often around 1 cubic yard, so small pours are usually cheaper bagged.
Concrete pricing varies significantly by region, supplier and mix, so we don’t publish a national figure. As a rule of thumb, bagged mix is cheaper for pours under about a cubic yard, while ready-mix delivery becomes more economical above roughly three — though most suppliers add a short-load fee below 8–10 yards. Use the calculator above to get your quantity, then get a local quote.
For small pours, bags usually win. For anything above about three cubic yards, ready-mix is normally cheaper per yard and far less work. The crossover point depends on your supplier’s short-load fee, which typically applies below 8–10 yards. Work out your volume above, then price both ways before ordering.
| Pour volume | Usually cheaper |
|---|---|
| Under 1 cubic yard | Bagged mix |
| 1–3 cubic yards | Depends on short-load fee — price both |
| Over 3 cubic yards | Ready-mix delivery |