If you have a VOM (volt-ohm-milliampmeter), you can measure the resistance of the element. If you can verify the voltage rating (maybe the cord is still connected and you can tell by the plug), then you can calculate the wattage by the formula P = V^2/R. That's the voltage squared divided by the resistance.
For 240 volt:
a 5500 watt element would have a resistance of about 10.5 ohms
P = (240)^2/10.5 = 5486.
For 115 volts:
a 1500 watt element would have a resistance of about 9.6 ohms
P = (120)^2/9.6 = 1500