For trhose who really care the world standard scale for HO is 1/87th not ish the only real flexibility in the scale, not "gauge is in the wheelsets and other strictly operational factors.
1/64 is I believe S scale : N-scale is 1:160 etc.
If you want to find the true scale to mm conversion formula you may Google it but the genrally accepted conversion seems to be:
Divide 1610 by the mm yields scale and divide 1610 by scale yields mm
example: 1610/30mm equals 1:53.6667 scale
example 2: 1610/28mm equals 1:57.5 scale
Mongoose seems to stick very close to a true scale on their SST figures while GW figures are of an heroic (i.e. grossly distorted semi-scale).
If you are truly concerned with compatibility with your current figure collection then purchase only one or two figures (when available) and compare them to your current figures.
Only you can judge whether you consider the figures from different companies as suitably compatible on your gaming table.
Each company seems to follow their own whim about actual scale versus what they regard as visual appeal.
This is why I now prefer Hiostorical miniatures that are designed to an actual scale.
Hope this is of some help to you.
