Here is a bit of guidance on my belt sizing and measurements. Traditionally the saddlery trade works in inches but you can use the Metric size guide to convert this easily.
Adult Classic, Wye Valley & Marshalsay belts have 7 holes spaced 1″ (25mm) apart.
Plaited, Laced & all Ranger belts have 5 holes spaced 1″ (25mm) apart.
The size indicates the measurement from the buckle, (but not including it) to the tightest (first) & loosest (last) holes. My sizing is based on the belt being usually fastened around the middle holes, but this is entirely your choice if you prefer a longer or shorter overlap, adjust the size ordered as required!
Use the guide below to choose the best size for your needs. 
Please contact me if you'd like any variation to these standard sizes.