On most vehicles there will be a vin plate on the inside of the drivers door. On there, there will be 4 weights.
- Your Gross Vehicle Weight
- Gross Train Weight
- Front Axle Weight
- Rear Axle Weight
From these numbers you can work out your towing capacity by subtracting the gross vehicle weight from the gross train weight. This will be able to tell you whether you can tow a trailer, horse box, or caravan.