I've recently started on a Wales setup, beginning in Gwent and have decided to attempt to scale all my Wales graphics to the same standard:
1. Original vehicle length or height measurement obtained and converted to mm
2. Scaled to 1:76
3. Applied new measurement as pixels by width or height respectively.
South Wales FRS ALP:
1. No original measurements able to be obtained, however I found this page stating an ALP to have a height of 3.55m (3550mm)
2. 3550 @ 1:76 scale = 46.7 (pixels must be a whole number so rounded up to 47px
I've done this with a number of vehicles that I've started using and made a quick comparison graphic to show the relative size difference between a few vehicles:
Silhouettes of people are based on an assumption of 6ft height converted to mm in 1:76 scale (px). Dog scaled based on average German Shephard height scaled 1:76 in px.
*Edit for clarification: Vehicles shown in the "Fleet list" are not all mine! Just re-scaled versions of other people's creations that I use personally on my setup*