If you buy cycling tyres with a width 25 mm this does not automatically mean they are exactly 25 mm or 25,4 mm (1 inch).
I have collected some data from my road bike.
|Tyre||Size||Rim (inside)||Pressure||Width front tyre||Width back tyre|
|Continental Grand Prix 4000S ii (folding)||25-622||17 mm||7.0 bar||27.1 mm||27.3 mm|
I will update this table when more data is available.