Source: Amps to volt-amps (VA) conversion calculator

 

So, I think what an electrician is trying to determine is what is the potential load on the transformer, which is typically rated in kVA (kilo volt amps). KVA takes losses into consideration, but is roughly the equivalent of kW. So in the above calculation, 16A/240V charging is 3.84kW, or 3840 watts.

So, this is a measure of the watt loads from all of the circuits on the main panel to determine the impact on the transformer feeding power to your home. In other words, would the utility need to upgrade your service to run the loads you intend to use.

 

As long as the power factor is close to unity (1), you can use VA and watts interchangeably. Lots of motors would reduce the PF, but homes don't typically have enough motors to make a significant difference, so Va should be fine. If your PF was low, the utility would be charging you extra for it.

I'd be very very surprised if your transformer doesn't have enough headroom to handle whatever your electrical panel can handle. I just replaced my 100A panel with a 150A one and there was no need to make any changes to the xformer or the incoming wires. My house is 50 years old.

 

If the OP is asking about watts then 16A times 240VAC is near total Watts but you have to put some overhead on it to run a calculation.
An example of last night charging plus hot tub and small ac use.

 

The distinction between kVA and kW is subtle and probably more involved than anyone wants to fully explain. As luck would have it, I'm almost certain that the built-in charger in the Bolt is PFC (power factor correcting) so it's power factor is going to be more or less 1 and so kVA = kW. But, when budgeting loads, it can't hurt to round up just so you always have a little bit of extra safety factor. So, 4kVA is a good round number.