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
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?