Whenever I've come across notation for specifying how much reinforcing steel is in a member, it is typically by giving the area of steel as a percent of the cross-sectional area of the member.

enter image description here

For example in this picture, you could say that the reinforcing steel is 0.02 or 2%. You could also specify the reinforcing steel given a schedule, e.g. #8 @ 12" O.C.

I recently came across a piece of software that was asking for the reinforcing steel of a floor slab in units of mm^2/mm. I cannot figure out how they came across those units. How could I calculate the reinforcement in these units given I know how much steel is in the slab in the other conventions I listed earlier?


1 Answer 1


Your second bar description is what you need to compare it to:

#8 @ 12" O.C.

A #8 bar is 0.79 in2. This gives us $\frac{0.79in^2}{12in}$ or in2 over in. This is the similar to your mm2/mm. (Obviously the units are not interchangeable!)

This method of describing reinforcing is useful if you don't care about the actual size of rebar used. It could be #8 at 12" or #6 at 6.625".

  • $\begingroup$ mm2/mm is not going to be the same as in2/in, you'll be out by a factor or 25.4. 1 inch = 25.4 mm. 1 in2/in is (25.4)^2/25.4 mm2/mm = 25.4 mm2/mm $\endgroup$
    – Fred
    Mar 7, 2015 at 4:38

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.