Q:

Is "steepness" a proper word? 

I am a marketing writer and am working on a product description, which would be as follows:

We track cool metrics like location, duration, speed and steepness. 

Is that use of the word correct?   Any insight would be wonderful. 

A:

I humbly suggest degree of incline or just slope:

The grade (also called slope, incline, gradient, pitch or rise) of a
  physical feature, topographic landform or constructed element, refers
  to the amount of inclination of that surface to the horizontal.