[odinsgrandson]

Scale 25/28 mm
Ratio 1:73.152

28 mm is the size that Games Workshop makes its models, but as they are "heroic scale" eg, have big hands and heads when getting buildings or vehicles to match them 1/48 or 1/50 scale looks better.

They started out as "Heroic 28mm" scale and they've been getting more and more heroic as time has gone on. The Scale Creep hasn't altered the stated size of the minis.

Currently, you can compare Citadel minis against 32mm minis, and they'll be the same scale (sometimes a little bigger).

Except for the Lord of the Rings minis. They aren't quite so heroic, it turns out.