Measure a concrete pour before choosing bags or delivery

Start with the actual shapes being filled. A slab footprint, edge thickening, column and post hole may need different geometry. Split the work into labelled parts before deciding whether to order bagged mix or delivered concrete.

Calculate the main slab

For an illustrative 4 m × 3 m slab at 100 mm thickness, convert 100 mm to 0.1 m. The base volume is 4 × 3 × 0.1 = 1.2 m³. These dimensions describe a quantity example, not a structurally suitable slab design.

Add only the extra depth of a thickening

Suppose a 4 m edge strip is 0.3 m wide and reaches a total depth of 0.3 m. The main slab calculation already includes the top 0.1 m over that strip. Add 4 × 0.3 × (0.3 − 0.1) = 0.24 m³, giving 1.44 m³ overall. Adding the full strip volume would count part of the slab twice. At intersecting edge strips, check overlapping corners too.

Review the prepared excavation

Plan dimensions may differ from formed or excavated dimensions. Check levels and thickness changes before ordering. Where depth varies, use measured sections or a defensible average for a simple linear variation; a single average cannot describe every irregular excavation.

Translate the quantity into an order

Keep the measured 1.44 m³ separate from any allowance. If an illustrative 5% allowance is selected, the adjusted figure is 1.512 m³. Confirm delivery increments, access and placement arrangements with the supplier. Concrete grade, reinforcement, cover and foundation dimensions must come from the project design.

Found a measurement or calculation issue? Send the example and your correction.