How much concrete do you need? Multiply length × width × thickness (all in feet), then divide by 27 to get cubic yards. For example, a 10 × 10 ft slab at 4 inches thick needs 1.24 cubic yards.
The free calculator below does it all for you: enter your measurements and get cubic yards, bags of concrete, truck loads and cost instantly , for slabs, footings, walls, columns, post holes, stairs and more. Switch between feet/inches and meters/cm at the top.
Last updated: October 2026.
Concrete Calculator
How much concrete do you need? Enter your measurements: get cubic yards, bags, trucks & cost instantly.
Estimates only. Bag yields per manufacturer specs (80 lb ≈ 0.60 ft³, 60 lb ≈ 0.45 ft³, 40 lb ≈ 0.30 ft³). Ready-mix trucks carry ≈ 10 yd³. Always round up and confirm with your supplier.
How to use the concrete calculator
1. Choose your shape from the tabs: Slab, Footing, Wall, Column, Post Holes, Circle Slab, Curb or Stairs. 2. Enter your measurements. Use the toggle at the top to switch between feet/inches and meters/cm. 3. Set a waste margin (10% is a safe default) and add your price per cubic yard if you want a cost estimate. 4. Read your results: cubic yards, cubic feet, cubic meters, bag counts (40, 60 and 80 lb bags), truck loads and material cost. The extra tabs cover special jobs: Bags converts any volume to bag counts, Mix Ratio works out site-mix materials (1:2:4), Rebar estimates bar lengths for slabs, and Cost & Coverage handles pricing and coverage in one place.
Concrete volume formulas
Every result on this page comes from these standard volume formulas:
| Project | Formula |
|---|---|
| Slab or footing | Length × Width × Thickness ÷ 27 = cubic yards |
| Wall | Length × Height × Thickness ÷ 27 = cubic yards |
| Round column or pier | π × radius² × Height |
| Circular slab | π × radius² × Thickness ÷ 27 = cubic yards |
| Stairs (solid) | ½ × total run × total rise × width |
How many bags of concrete do I need?
Bagged concrete yields (per manufacturer specs): an 80 lb bag makes about 0.6 cubic feet, a 60 lb bag about 0.45, and a 40 lb bag about 0.30. Since one cubic yard is 27 cubic feet, a full yard needs 45 eighty-pound bags. As a rule of thumb: for anything under about one cubic yard, bags are practical. Above that, ready-mix from a truck is usually cheaper and far less work.
| Project | 80 lb bags, incl. 10% waste |
|---|---|
| 10 × 10 ft slab, 4 in thick | 62 |
| 12 × 12 ft slab, 4 in thick | 88 |
| 10 post holes, 10 in wide, 3 ft deep | 30 |
How much area does one cubic yard cover?
Coverage depends on thickness: the thinner the pour, the further a yard goes:
| Thickness | Area covered by 1 cubic yard |
|---|---|
| 4 inches | 81 sq ft |
| 5 inches | 65 sq ft |
| 6 inches | 54 sq ft |
| 8 inches | 41 sq ft |
| 12 inches | 27 sq ft |
Tips for ordering concrete
Always add 5 to 10% for waste: spillage, uneven ground and formwork gaps eat into your estimate. A standard ready-mix truck carries about 10 cubic yards; small loads often carry a short-load fee, so ask your supplier. Buying bags? Get a few extra, running short halfway through a pour is worse than having leftovers. And always confirm your final quantity with your supplier before ordering.
How much concrete does a truck carry?
A standard ready-mix truck carries about 10 cubic yards. If your order is much smaller, ask about short-load fees, which many suppliers add for small deliveries. For very small jobs (under about a yard), bagged concrete from a hardware store is often simpler.
How much does concrete weigh?
One cubic yard of concrete weighs about 4,000 pounds (roughly 1.8 metric tonnes). That matters if you are planning transport, or checking what your ground and formwork can handle.
How long does concrete take to cure?
Concrete hardens in stages. You can usually walk on a new slab after 24 to 48 hours. Most guides say to wait at least 7 days before driving on it. It keeps gaining strength for about 28 days.
Frequently asked questions
How much concrete do I need for a 10×10 slab?
At 4 inches thick, 1.24 cubic yards (about 62 eighty-pound bags including 10% waste).
How many 80 lb bags are in a cubic yard?
45. (27 cubic feet ÷ 0.6 cubic feet per bag.)
How thick should a concrete slab be?
4 inches is standard for patios and garden paths; go 6 inches for driveways or anything carrying vehicles.
What is the 1:2:4 concrete mix ratio?
1 part cement, 2 parts sand and 4 parts aggregate by volume (a common site-mix recipe). Use the Mix Ratio tab above to work out exact quantities.
How much does concrete cost per cubic yard?
It varies a lot by region and supplier. Enter your local price per yard in the calculator’s price field for an instant cost estimate.
Should I order extra concrete?
Yes. A 5 to 10% waste margin covers spillage, uneven subgrade and slight formwork movement.
How many 60 lb bags of concrete are in a yard?
60 bags. (27 cubic feet divided by 0.45 cubic feet per bag.)
How much does one yard of concrete weigh?
About 4,000 pounds (roughly 1.8 metric tonnes).
How much concrete fits in a mixer truck?
About 10 cubic yards in a standard truck.
What is a short load fee?
Many ready-mix suppliers charge extra when you order less than a full truckload. Ask about it when getting quotes.
How long does concrete take to dry?
You can usually walk on it after 24 to 48 hours. It keeps hardening for about 28 days.
When can I drive on new concrete?
Most guides recommend waiting at least 7 days before driving on it.
Can you pour concrete in the rain?
Light rain is usually fine. Heavy rain can damage the surface, so cover fresh concrete if a downpour is expected.
What is the difference between cement and concrete?
Cement is the powdered binder. Concrete is the finished building material made from cement, sand, aggregate and water.
Do I need rebar in a 4 inch slab?
Rebar or steel mesh helps control cracking. For a simple garden patio many people skip it, but for driveways it is strongly recommended. Check your local building code.
How do I work out concrete for an odd shaped area?
Split the shape into rectangles and circles, work out each part, add them up, then add your waste margin.
How deep should footings be?
It depends on your soil and the local frost line. A common rule is to dig below the frost line. Check your local building regulations.
Is it cheaper to mix my own concrete or order ready-mix?
For under about a yard, bags are usually fine. For bigger pours, ready-mix is normally cheaper per yard and far less labour.
How many bags of concrete do I need for a fence post?
A typical post hole (10 inches wide, 3 feet deep) takes about 3 eighty-pound bags. Use the Post Holes tab above for your exact holes.
Does the calculator include waste?
Yes. The waste margin selector adds 5, 10 or 15 percent on top of the exact volume. 10 percent is selected by default.