Explanation of the Numbering Scheme

Baldwin Pannier Tank Locomotives

This description is from the catalogue of Baldwin erecting card drawings as published by DeGolyer Library of Southern Methodist University in Dallas, Texas:

The Baldwin class number was a rather complicated classification system initiated in 1842 and used until some time around 1940. The class number for the Nevada-California-Oregon Railway (sic) can be described in the following manner.

10-24 D 35


10 = Indicates a total of 10 wheels

24 = Number represents size of cylinders

D = 3 pairs of driving wheels

35 = Indicates the 35th locomotive in the class


  • The initial number is the total number of wheels of all kinds under the locomotive.
  • The second number indicates the cylinder diameter in inches, this quantity being obtained by dividing the cylinder diameter by 2 and adding 3 to the quotient. The above classification number of 24 indicates a cylinder diameter of (24 divided by 2) + 3 = 15". A fraction, e.g. 42/68 indicates a compound locomotive having two cylinders.
  • The letter designation indicates the number of pairs of coupled driving wheels. "A" = special class of high speed geared locomotive with one pair of driving wheels. Also rack railroad locomotives. "B" = one pair of driving wheels. "C" = two pairs of driving wheels. ... "F" = five pairs of driving wheels. Double letters = articulated locomotives having more than one set of driving wheels.
  • The last number(s) in the class number identifies a specific locomotive within the class [although the numbering is not contiguous.]

Therefore 10-12-D represents 10 wheels, 9 inch cylinders, and 3 coupled axles.

I am grateful to Martin Coombs for this information.

See Also