Concrete yard calculator
Measure your slab. Get the volume, waste allowance and bags in one place.
Calculating example…
Estimates only · see assumptions below
Your material estimate
Example estimate— yd³
- Cubic feet
- —
- Cubic meters
- —
Shape assumption. Flat, rectangular slabs of uniform thickness. Slabs are added before waste. Overlapping areas must be measured only once.
Or use premix bags
Choose one row. Whole bags rounded up after waste.
| Bag size | Typical yield | Bags |
|---|---|---|
| 80 lb | 0.60 ft³ | — |
| 60 lb | 0.45 ft³ | — |
| 40 lb | 0.30 ft³ | — |
Typical values; use the yield on the bag label. These are concrete premix bags, not plain cement.
Volume × your $/yd³. Excludes tax, delivery, short-load fees, labor and equipment. Truck capacity and minimum orders vary.
Enter positive dimensions to see a material estimate.
Estimates only. Displayed volumes use 3 decimals; calculations and bag rounding use unrounded values. Confirm supplier increments before ordering. Not construction, commercial or tax advice.
How to calculate
- Measure the shape shown above. Use the unit labels beside each field.
- Choose a waste allowance from 0–30%. The example starts at 10%.
- Read the waste-adjusted volume or choose one bag size. Add a material price if you have a quote.
- Copy or print the estimate, then verify the mix yield and order increments with your supplier.
The formula
Volume (ft³) = length (ft) × width (ft) × thickness (in) ÷ 12. Add the unrounded volumes of all slabs. Cubic yards = cubic feet ÷ 27.
Waste-adjusted volume = measured volume × (1 + waste percent ÷ 100). One cubic foot is 0.028316846592 cubic meters. Bag counts round up once; displayed volumes round to three decimals.
Worked example
20 ft × 10 ft × 4 in ÷ 12 = 66.666667 ft³. With 10% waste: 73.333333 ft³ ÷ 27 = 2.716049 yd³. At $150/yd³: $407.41. That is 123 typical 80 lb bags.
Ready-mix material cost = waste-adjusted cubic yards × your price per cubic yard. A bag cost, when entered, is whole bags × price per bag. Neither cost includes delivery, tax, short-load fees, labor or equipment.
Geometry estimates material only. It does not select concrete strength, reinforcement, dimensions or a construction method.
Frequently asked questions
How many yards is a 20 × 10 slab at 4 inches?
The measured volume is 2.469136 yd³. With the default 10% waste allowance, the estimate is 2.716049 yd³. Confirm the ordering increment with your supplier.
Do I enter thickness in inches or feet?
In US mode, thickness is in inches while length and width are in feet. Metric mode uses centimeters for thickness and meters for length and width.
Can I add a driveway and a sidewalk?
Yes. Choose Add another slab, enter each rectangular section, and the tool sums their volumes before applying one waste percentage. Do not count the same area twice.
Why add 10% waste?
It is an editable planning allowance for uneven forms and handling losses, not a construction standard. You can choose 0–30%; site conditions may need a different allowance.
Does the price include delivery and labor?
No. It multiplies the waste-adjusted cubic yards by your material price per cubic yard. Delivery, short-load fees, minimum orders, tax, pumping, reinforcement and labor are excluded.
Can this tell me how thick my slab should be?
No. Thickness is an input, not a recommendation. Ask a qualified professional about loads, ground conditions, reinforcement and local requirements.