Using a Margin of Safety: Problems Caused by Underestimating the Amount of Concrete

Never try to order the exact amount of needed concrete. Include a margin of safety.

A perfectly placed order of concrete will finish the job with a small amount left over. A 20 cubic yard order with 1 cubic yard left over is a good order. A 20 cubic yard order that comes up cubic yard short is not a good order.

Extra costs of coming up short of concrete

  • Overtime for the crew

  • A short load charge from the ready mix supplier

  • A cold joint can occur (where one pour ended and another pour began)

Three steps to ordering enough concrete

  • Use the concrete calculator

  • Figure depths and widths as they have been built on the site, not simply what the plans say.

  • Add a margin of safety

Rule of Thumb for Margin of safety

If your order is Order this much extra
1-5 cubic yards .5-1 c.y. extra
6-10 c.y. 1 c.y. extra
11-20 c.y. 1-1.5 c.y. extra

It can be upsetting to end up with any extra concrete. You are having to pay for this concrete after all. However, realize you are doing your job a service by ordering enough concrete - which means you are going to have a little concrete left.

Return to How much concrete do you need?

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