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Model Railroad calculator

These tools will help you calculate common conversions and lookup tables for model railroad standards.
The NMRA RP-20.1 Car Weight formula:
Scale Ratio Base Weight (oz) Additional weight (oz)
per inch of car body length
O 1:48 5 1
On3 1:48 1.5 0.75
S 1:64 2 0.5
Sn3 1:64 1 0.5
HO 1:87 1 0.5
HOn3 1:87 0.75 0.375
TT 1:120 0.75 0.375
N 1:160 0.5 0.15

NMRA Car Weight Calculator

The National Model Railroad Association (NMRA) has recommendations for freight car and passenger car weight (based on RP-20.1 Car Weight).

This calculator will help you calculate the correct weight for your car.

Units
Scale
Car length in ()
Recommended Weight ()

The AMRA Carriage Mass Standard formula:
Scale Ratio Passenger (g/mm) Freight (g/mm)
F…G 1:19

1:24
1.50 2.00
1-Gauge 1:32 1.10 1.50
O 1:43.5

1:48
0.80 1.10
S 1:64 0.55 0.75
OO
HO
1:76
1:87
0.40 0.55
3mm
TT
1:100
1:120
0.30 0.40
N 1:148
1:160
0.22 0.30
Z 1:220 0.16 0.22

AMRA Car Weight Calculator

The Australian Model Railroad Association (AMRA) has recommendations for freight car and passenger car weight based on the length of the car, for both freight and passenger cars.

This calculator will help you calculate the correct weight for your car.

Units
Scale
Car length in ()
Recommended Weight Freight ()
Recommended Weight Passenger ()

The Normes Européennes de Modélisme NEM-302 formula:
Scale Ratio Weight (g/mm)
II / F / G 1:22.5 4.00
1-Gauge 1:32 2.00
O 1:48 1.00
S 1:64 0.60
HO 1:87 0.40
TT 1:120 0.25
N 1:160 0.17
Z 1:220 0.12

NEM Car Weight Calculator

The Normes Européennes de Modélisme (NEM) has recommendations (NEM 302) for car weight based on the length of the car.

This calculator will help you calculate the correct weight for your car.

Units
Scale
Car length in ()
Recommended Weight ()