NMRA Recommended Practices
Car Weights

The following table is extracted from the National Model Railroad Association Recommended Practice RP-20.1. You can find a full presentation of the information at: NMRA Car Weights. Once there you will find a full explanation and rationale for these values.

Scale Initial Weight
(ounces)
Add Additional Weight
per inch of car body length
(ounces)
O 5 + 1
On3 1 1/2 + 3/4
S 2 + 1/2
Sn3 1 + 1/2
HO 1 + 1/2
HOn3 3/4 + 3/8
TT 3/4 + 3/8
N 1/2 + .15
For example, imagine an 8-inch long S-Scale box car. Start with 2 ounces. Then add 8 * 1/2 or 4 more ounces
for a total of 6 ounces. I have a Flyonel box car which is nearly 8-inches long and weighs almost exactly that. So, I will not add any weight to it.


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