If I told you my truck has 200 horsepower, could you tell me the cargo weight capacity? Not really. There are more factors than just the motor specs that play into your assessment. You might be able to ball-park it, but be prepared to be off by a factor of 2 or more. Here's why...
A motor needs current to produce torque. The available power supply current comes into play.
Total power available depends on both current and voltage. If you run your motor at a higher voltage (without saturating the back iron) you will have more power available for a given current.
Every motor has a torque vs speed inverse relationship. How fast you want the device to go affects how much torque each motor can generate.
The gear trains (or other transmission) and frictional losses also affect the capability to operate at given torque and speed.
You can use the ratings of the motors to get you in the ballpark. They can tell you the maximum power available to be transmitted to the device. However, the other factors play more than a nominal role.