GWR engines carried painted-on numbers until around 1876, at which point the standard cast numberplate illustrated here were introduced. These were carried more or less unchanged even beyond the end of the GWR. Exceptions included locos such as the 3232 Class, which carried separate numbers in an arc on the rear splasher. Some absorbed locos had the words "GWR" above the number.

Tender engines carried the number plates on the cab side. Tank engines at first had the numberplate on the center of the tank sides, but from around 1907, these were moved backwards to the rear of the side tanks (small engines) or the bunker sides (larger engines).

The illustration shows a lined plate, as carried by locos that were fully lined overall. The example seen here stems from the unlined 14xx class, so would in reality not have been lined in GWR days.