How to select unit for area of nodes in grd2xyz -Wa?

I want to create an histogram from a geographic grid, so I used grd2xyz to extract the z-values.
And also I use the -Wa argument to compute weights equal to the area each node represents. I think that this values are in km2. Is it possible to choose another unit (m2, sq miles, etc)? Should I use gmtmath?

I know that for an histogram and can do it with the weights in km, but since it is a very large file, I want to store the result as integer in binary (probable unsigned short 2-byte integer) and I can’t do it is the units are in km2.

For now you will need to use gmtmath I think, but you can also open a feature request to allow other units t one used, say via -Wa+ue for meter^2.