Concrete Volume Calculator
Work out exactly how much concrete your project needs. Calculate slabs, footings and cylinders in cubic metres, cubic feet and estimated bags.
Last Updated: June 2026
Project details
Material summary
Cubic metres
1.32 m³
Cubic feet
46.6 ft³
20kg bags (est.)
147
Includes 10% waste allowance
For volumes above roughly 1 m³, ordering pre-mixed concrete by the truck is usually more economical than mixing bags by hand.
Bag estimates assume a 20kg bag yields about 0.009 m³ and an 80lb bag about 0.017m³. Always confirm coverage with your supplier, as yields vary by product.
How This Calculator Works
This calculator finds the volume of your pour from its dimensions, then converts that volume and estimates how many bags you need.
Slab or footing volume = length × width × thickness
Cylinder volume = π × radius² × height
Cubic feet = cubic metres × 35.31
Example:a slab 4m long, 1m wide and 0.1m thick has a volume of 4 × 1 × 0.1 = 0.4 cubic metres, which is about 14.1 cubic feet.
Bag count estimate:divide the total volume by the yield of a single bag. A typical 20kg bag yields roughly 0.009 cubic metres, so the slab above needs about 0.4 ÷ 0.009 ≈ 45 bags. The calculator adds a 5% waste allowance, so it would suggest ordering around 47 bags to cover spillage and uneven ground.
How to calculate concrete volume
Concrete volume is simply the space your pour will fill. For a slab or footing, multiply the length, width and thickness in metres. For a round form such as a post hole or column, use the formula for a cylinder: pi multiplied by the radius squared, multiplied by the height.
Once you know the volume in cubic metres, you can convert it to cubic feet or estimate the number of bags needed. The calculator above handles all three project shapes and the conversions automatically.
Common concrete project examples
A small garden path might be 4m long, 1m wide and 0.1m thick, giving 0.4 cubic metres. A strip footing 10m long, 0.3m wide and 0.4m deep needs 1.2 cubic metres. Four post holes 0.3m in diameter and 1m deep total about 0.28 cubic metres. Use the tabs above to model whichever shape matches your job.
Concrete ordering tips
Always order a little more than the exact calculated volume to allow for spillage, uneven ground and slight over-excavation. For larger pours, ready-mixed concrete is usually more economical and consistent than bags. Confirm access for the truck, have enough people ready to place and finish the concrete quickly, and check the recommended mix strength for your application.