you can easily work it out - add up the wattages and divide by 12
I.e. 100w per headlight and 20w for a taillight running from the same fuse (for example)
as power=amps*voltage : amps=power/voltage
=20 Amps load on the system
If you're running a 20 Amp fuse for the headlights then this is right on the limit. Also bear in mind that these headlights can be +/- 20% on the wattage ratings and the voltage in the car is more likely 13.8 volts than 12.