ESPJ Construction Corp. Concrete Specialist

Rule of Thumb for Margin of safety
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.

Requesting Your Ready Mix Supplier to Visit Your Site

After you have chosen a Ready Mix Supplier, have a representative come to your site to give his/her opinion on the quantity required. Compare the figure with what you came up with. Discuss any variances with the supplier.

Your ready mix supplier is invaluable for checking your view of job conditions, checking your margin of safety, identifying issues you may not have thought of, and informing you of any local conditions you need to be aware of.

Estimating Concrete Steps
Estimating Concrete Steps
Steps seem tricky to calculate but are not. If there are three steps leading up to a porch:
Use the slab calculator to figure the concrete needed for the porch surface.
Use the footing calculator to calculate the sides of the porch and the steps
Here is an example:
This porch has 9 sq. feet of porch surface, so enter in the slab calculator 4" thickness by 3' width by 3' length. This totals .11 cubic yards.
The porch also has 9 linear feet of 6" step. So enter in the footing calculator, 6" depth by 12" width (always figure steps with a 12" width) by 9' length. This totals .17 cubic yards.
The total concrete needed for the 3' by 3' porch will be .28 cubic yards. (.11 + .17 cubic yards = .28 cubic yards)
Repeat this for added layers of steps.

Calculating The Amount of Base Fill.
Granite Construction has an excellent base fill calculator on their site. Use this to figure how much material you need for the subgrade.
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