In what way do units matter when providing density for Collider2Ds?

If I were to assume spatial units in my game as feet, would I need to assume lbs/ft^3 as my units for density? Does this only matter when I apply forces to objects, so that I can predetermine how the units I should interpret force to use? I am trying to take advantage of Rigidbody2d.useAutoMass, but need to know the ratio for densities first.

For example, when I give a 1x1x1 cube a density of 1 (in 2d mode with a 2d rigidbody and box collider) its mass is auto-calculated to 1. If this were water, the mass of 1 cubic meter of water is 1 metric ton, so the units for density are tons / m ^ 3 and the density should be 1. Converted to feet, the mass of 1 cubic foot of water is 62.427lbs, so the units for density are lbs / ft ^ 3 and the density should be 62.427. I don't know how much force it takes to move this one foot per second, but if I did it would help to know how to apply this example to other substances like wood and metal.

I really need to figure this out, and the documentation provides no examples. I'm using a variety of physical materials and I can't just test every object to see if it behaves like it has the right mass for its size. Same with drag, to be honest.