How to Calculate Concrete Volume

1. Measure the concrete shape

Use dimensions from the project plan and measure the inside dimensions of the formed pour where appropriate. Split an irregular pour into simple sections, calculate each one, then add the volumes.

The calculator supports rectangular slabs, strip footings, walls, cylinders, and round post holes with a round post occupying the entered concrete depth.

2. Convert dimensions before multiplying

For an imperial slab, convert thickness in inches to feet by dividing by 12. For a metric pour, keep length, width, and thickness in metres. The exact international conversions used here are 1 in = 0.0254 m, 1 ft = 0.3048 m, and 1 yd = 0.9144 m.

Imperial example: 10 ft × 10 ft × 4 in

Convert 4 in to feet: 4 ÷ 12 = 0.333333… ft. Net volume = 10 × 10 × 0.333333… = 33.333… ft³, or 1.234567… yd³. At a chosen 10% allowance, the planning amount is 36.666… ft³ or 1.358024… yd³, displayed as 1.36 yd³.

At a product yield of 0.60 ft³ per bag, 36.666… ÷ 0.60 rounds up to 62 whole bags. The yield must match the exact product label.

Metric example: 3 m × 4 m × 0.10 m

Net volume = 3 × 4 × 0.10 = 1.20 m³. With a chosen 5% allowance, the planning amount is 1.26 m³. That equals about 1.65 yd³. The allowance is a separate choice; it is not part of the geometric volume.

3. Apply allowance and purchasing rules separately

A planning allowance can account for conditions such as uneven excavation or handling loss, but there is no single percentage that fits every site. Choose it with reference to actual measurements and supplier or contractor advice.

Keep material volume, bag rounding, and supplier order increments distinct. Bag quantities round up to whole bags. Ready-mix order amounts may follow a supplier's minimum or increment; ask for that rule and calculate it explicitly.

• Net volume = geometric volume × number of identical pours.
• Planning volume = net volume × (1 + allowance percentage ÷ 100).
• Whole bags = ceiling(planning volume ÷ mixed yield per bag).

Check the estimate

Check the units shown beside every input, confirm dimensions against the plan, and compare the result with the calculation breakdown. This is a material quantity estimate; it does not set safe slab thickness, footing dimensions, reinforcement, or building-code requirements.