# How do units of mm^2/mm represent the reinforcing steel area in a slab?

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.

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?

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!)