Expert: Dan Griffin - 9/11/2008

Question
HI,
Hoping that you are fine. Can you please tell me some rules
of thumb to estimate the quantity of cement, steel, sand ,
aggregate for a small project??

Regards

Answer
Makhzumi, concrete is a mixture of cement, stone, and sand.  Concrete is measured and estimated based on cubic volume.  The proportions of cement, atone, and sand vary depending on ultimate strength and other properties desired.  In the US we would use the concrete's compressive strength rating like 2500# or 3500# concrete.  In the US we use the cubic yard as a measuring unit for the volume, it is very important to keep the multipliers in the same unit size to derive cubic measure.  Example:
Concrete slab for a patio.  The concrete will measure 10 feet by 20 feet by 4" thick.  You must change the units to all feet or all inches.  I use feet, so 10 x 20 x 4/12 (.33333) =  66.66666 cubic feet.  Each cubic foot will weigh about 150 pounds.

There are 27 cubic feet of concrete in a cubic yard, so divide the 66.6666 by 27 to derive cubic yards - 2.469 cubic yards, about 10,000 pounds of material.  One formula for concrete uses the proportions of 1 part cement, 3 parts sand, 5 parts gravel.  1/9 cement, 3/9(1/3) sand, 5/9 gravel.

I hope this gives you the information you need.  If you have your data when you order the material, this supplier will surely help you double check your information.

Rebar is more a matter of shape, thickness, and strength required, not a simple matter of concrret quantity.