How to determine amp rating ?

[Tat2]

It comes from the specs that TRX lists in the manual.

"VXL-3s Specifications:
Input voltage: 4.8 - 11.1V (4 - 9 cells NiMH or 2S - 3S LiPo)
Supported motors: Brushed / Brushless / Sensorless brushless
Motor limit: None
Continuous current: 200A
Peak current: 320A
BEC voltage: 6.0V DC
Transistor type: MOSFET
On-resistance: 0.00075 Ω Max (0.006/8 FETs)
PWM frequency: 12,000Hz
Battery connector: Traxxas High-Current Connector
Motor connectors: TRX 3.5mm bullet connectors
Motor/battery wiring: 12-gauge Maxx® Cable
Thermal protection: 2-stage thermal shutdown
Case size (l/w/h): 55mm (2.19")/ 39mm (1.54")/ 33mm (1.3")
Weight: 109g (3.84oz)"