It doesn't really count if it was never usable.

Anyhow, to be useful: there are two basic units of measurement in Spring. Grid squares, and elmos. Elmos are used for measuring distance, velocity, etc. Squares are used for how much space a unit takes up on a map.

http://trac.caspring.org/wiki/UnitsOfMeasurement

Most games standardize on models that are 2x2 squares. S'44 uses models that are 1x1, and so has smaller unit-scale (in terms of usable units) than typical Spring games. Mobile units generally go up to 4x4 squares. This is a healthy upper-limit.

Buildings can go as large as you like, but you'll have to choose between having a big flat square of map or making the unit look good with bumpy map geometry underneath - we typically see buildings going up to 8x8, but there are exceptions that go higher. Air units can also get insanely huge and still work well, as demonstrated by Smoth's Gundam White Base (although even those have their warts).

Each square is 16 elmos on a side.

Mappers also talk of how many "screens" a map is, which is kind of arbitrary in a game with zooming. 512 elmos to the "screen". It's a holdover from OTA days. DeltaSiegeDry, the most popular is 20x10.