Ready-mix or bags of concrete?
Work out the volume first with the concrete calculator, then decide how to buy it. This page does not set a price or a minimum truck load.
Start with volume
Net volume is length × width × depth (or π × r² × depth × holes). Heidelberg Materials UK recommends adding 5–10% for spillages and uneven surfaces. The calculator defaults to 10%.
Bagged concrete
Tarmac states one 20kg bag of Blue Circle Multi-Purpose Concrete typically produces around 0.01 m³ of fresh concrete. Wickes gives the same 0.01 m³ figure for a generic 20kg pre-mix bag. Bags suit jobs you can mix and place yourself. Unused sealed bags can wait; a part-used bag cannot.
Ready-mix
Ready-mix arrives already mixed. Order about the calculator's waste-adjusted volume, then round up to your supplier's increment and check their minimum load. We do not publish a truck size or a minimum — that is supplier-specific.
How to choose
- If you can mix and place the bags before they set, bagged concrete is simpler to schedule.
- If the pour is continuous or the volume is large for one person, ready-mix is usually the practical route.
- Fence posts can use the Postcrete lookup table instead of a volume yield.
Get the volume first
The calculator shows net m³, order m³ and 20kg bag counts from the sourced yields.
Open the concrete calculatorSources: Tarmac Blue Circle Multi-Purpose technical sheet (0.01 m³/20kg bag); Wickes concrete category page (same yield); Heidelberg Materials UK ready-mix volume FAQ (5–10% waste). Read 26 October 2026.