Free job calculator
Concrete Calculator
Work out how much concrete you need — the volume in cubic metres and the number of 25kg bags, with waste added.
Volume needed
0 m³
25kg bags (approx.)
0
Incl. waste
0 m³
Bags are estimated at ~90 × 25kg bags per m³. For larger pours, ready-mix is usually cheaper.
How to work out concrete volume
Concrete is ordered by volume in cubic metres (m³). Multiply length × width × depth — all in metres. A slab 4m long, 3m wide and 100mm (0.1m) deep is 4 × 3 × 0.1 = 1.2 m³.
Add around 10% for waste — uneven ground, spillage and over-dig all eat into your pour. A 25kg bag of pre-mix makes roughly 0.011 m³, so figure about 90 bags per cubic metre; beyond ~0.5 m³, ordering ready-mix usually works out cheaper.
Concrete calculator FAQs
How much concrete do I need? +
Length × width × depth in metres = m³. Add ~10% for waste.
How many bags per m³? +
About 90 × 25kg bags per cubic metre once mixed.
Bags or ready-mix? +
Bags for small jobs; ready-mix delivered for larger pours — faster and usually cheaper per m³.
Priced the job? Now invoice it.
Invoice My Job logs your jobs and sends professional invoices in about 60 seconds — built for UK builders.
Get the App