Concrete Calculator

Estimate concrete for slabs, rectangular footings, and round columns. Calculate cubic yards and 40, 60, or 80 lb bags with quantity and an extra material allowance.

Updated

Length (ft)Width (ft)Thickness (in)
Dimension guide · Not to scale
Slab thickness
Width
Length

Concrete material estimate

Volume before allowance
1.235 yd³
Volume with allowance
1.358 yd³
Cubic feet with allowance
36.667 ft³
Cubic meters with allowance
1.038 m³

Choose one bag size

40 lb bags
123
60 lb bags
82
80 lb bags
62

Each bag count covers the full volume including 10% extra material; do not add the three counts together. Counts are rounded up from unrounded volume. Assumed yields: 40 lb = 0.30 ft³, 60 lb = 0.45 ft³, 80 lb = 0.60 ft³. Check your product label.

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How the concrete calculator works

Choose a slab, rectangular footing, or round column. Each dimension can use feet, inches, yards, meters, or centimeters independently. Select the unit beside each measurement; all dimensions are converted to feet before calculating volume.

For slabs and footings, volume is length × width × depth after converting dimensions to feet. For round columns, volume is π × radius² × height. Multiply by the number of identical items, then divide cubic feet by 27 to get cubic yards.

Concrete bags and extra material

The extra material allowance multiplies the net volume by 1 + allowance / 100. It defaults to 10%, which you can change to suit your project. Results show net cubic yards, volume including the allowance, and equivalent bag counts.

This concrete bags calculator assumes nominal yields of 0.30 cubic feet per 40 lb bag, 0.45 per 60 lb bag, and 0.60 per 80 lb bag. Divide the unrounded volume by the yield and round up to a whole bag. The three bag sizes are alternatives, not quantities to combine.

Frequently asked questions

How much concrete does a 10 × 10 foot slab need?

At 4 inches thick, the net volume is approximately 1.235 cubic yards. With a 10% allowance, it is approximately 1.358 cubic yards, or 62 bags at the assumed 80 lb yield.

How do I calculate several footings?

Enter dimensions for one footing and set the quantity to the number of identical footings. For different sizes, calculate each size separately and add their volumes.

Why can bag counts vary between products?

Bag weight does not guarantee the same finished volume for every mix. Check the yield printed on your chosen product before ordering.

Does this include rebar or labor costs?

No. This calculator estimates concrete material volume and bag counts only.

Estimate limitations

Measurements assume uniform thickness and simple solid shapes. Uneven excavation, spills, and supplier delivery increments can change the order quantity. Small displayed volumes may round to zero; bag counts still use the unrounded volume. Confirm dimensions and product yield with your supplier. This is a material estimate, not a structural design.

What's changed
  • Launched with slab, rectangular footing, and round column calculations.

References