Find the volume
For a rectangular slab or footing, multiply length × width × depth in the same unit. For a round column, use π × radius² × height.
ft × ft × in ÷ 324 = yd³
For metric dimensions: m × m × mm ÷ 1,000 = m³.
CONCRETE VOLUME & MATERIAL ESTIMATOR
Concrete Calculator
Calculate concrete volume, bags and material costs for slabs, footings and round columns. Enter your dimensions to get an estimate in cubic yards or cubic metres.
US & metric measurementsPublished bag yieldsFree to use
Published bag yieldsCalculations stay in your browserUS & metric in one place
METHOD & ASSUMPTIONS
How the estimate is calculated
The calculation separates measured volume, extra allowance and whole-bag rounding so you can check each step.
Give yourself a margin
Uneven ground, forms and handling affect the pour. NRMCA recommends a 4–10% allowance above plan volume for contingencies.
net volume × 1.10 = +10%
Our default is 10%. You can change it to suit your project.
Turn volume into bags
Divide the volume including allowance by the mixed yield per bag. Round up to a whole bag; a fraction of a bag won’t cover the estimate.
total ft³ ÷ bag yield = bags
Bag yields vary by mix. Use the value printed on your product.
A QUICK JOBSITE REFERENCEHow many bags
How many bags
in a cubic yard?
One cubic yard is 27 cubic feet. These bag counts use approximate yields for standard QUIKRETE Concrete Mix, before any extra allowance.
Check the manufacturer’s data sheet ↗| Bag size | Mixed yield | Bags / yd³ |
|---|---|---|
| 40 lb | 0.30 ft³ | 90 |
| 50 lb | 0.375 ft³ | 72 |
| 60 lb | 0.45 ft³ | 60 |
| 80 lb COMMON SIZE | 0.60 ft³ | 45 |
Using a metric bag or a different mix? Select “Custom yield” in the calculator and enter the mixed volume printed on the bag.
LET’S PUT IT TO WORKA 10 × 10 ft patio,
A 10 × 10 ft patio,
4 inches thick.
The slab needs 1.235 yd³ before allowance. Add 10% and the estimate becomes 1.358 yd³—or 62 bags of 80 lb mix at 0.60 ft³ per bag.
YOUR MEASUREMENTS
10 × 10 × 4 ÷ 324
Measured1.235 yd³
With 10% extra1.358 yd³
Whole 80 lb bags62 bags
PLANNING YOUR ORDER
Concrete calculator FAQs
Answers about measurements, bag yields and ordering quantities.
How do I calculate concrete for a slab?
Multiply the length in feet by the width in feet and the thickness in inches, then divide by 324. This gives cubic yards before allowance. In metric, multiply length and width in metres by thickness in millimetres, then divide by 1,000 for cubic metres. Use dimensions specified for your project; this calculator does not choose a safe slab thickness.
How many 80 lb bags of concrete do I need?
Divide the required cubic feet by your product’s yield and round up. Standard QUIKRETE Concrete Mix yields about 0.60 ft³ per 80 lb bag, so one cubic yard needs 45 bags before allowance. For a 10 × 10 ft slab at 4 inches thick with 10% extra, the estimate is 62 bags.
Does the bag count already include extra concrete?
Yes. The calculator applies your chosen allowance to the measured volume first, then calculates and rounds up the bag count. Don’t add the same allowance a second time. The result shows the measured volume and the extra amount separately.
Can I use this for footings, columns or post holes?
Use Footing for rectangular pours and Round column for cylinders. Enter the number of identical pours to multiply the quantity. Round mode calculates a full cylinder: if using it for a post hole, it does not subtract the space occupied by the buried post. Structural dimensions and concrete specifications should come from the project design.
Is it cheaper to buy bags or order ready-mix?
Open “Compare material costs” and enter your prices. Bag cost is the rounded bag count multiplied by price per bag. Ready-mix cost uses the greater of your required volume or the supplier’s minimum billed volume, then adds entered delivery and other fees. The comparison excludes labor, mixing equipment and taxes unless you include them in your prices. A minimum bill does not mean the calculator changes the volume needed for the pour.
How do I use 20 kg or 25 kg bags?
Select Metric units, then choose Custom yield and enter the mixed yield in litres stated on the bag. Bag weight alone does not determine the finished volume: different products have different yields. If the label says 0.01 m³, that is 10 litres.
Is concrete the same as cement?
No. Cement is a binder used in concrete, alongside aggregate and water. This tool estimates the finished concrete volume or bags of premixed concrete. It does not calculate a cement-only mix design or the separate proportions of sand, stone and cement.
Sources, precision & limitations
Concrete Calculator is a free quantity estimator. Calculations use unrounded values internally; displayed volumes are rounded for readability and bag counts round up. US-to-metric conversions use 1 foot = 0.3048 metres and 1 cubic yard = 0.764554857984 cubic metres. Changing units preserves your measurements.
Bag presets follow QUIKRETE’s published approximate yields. Allowance guidance follows NRMCA CIP 31; ordering considerations follow its ordering and scheduling guide. Unit conversion reference: NIST.
This tool estimates material quantities, not structural adequacy, mix design or an installation quote. Confirm your measurements and order with your supplier. No affiliation with the referenced manufacturers or associations.