At the risk of sounding stupid, I just need to do load cals for Nstar. Everything is rated in watts and they require kva
Watts = VA x PF (Power Factor), so of all you know is watts, then VA = W/PF
If the load is resistive in nature, i.e. incansecent lamps (lol) or resistive heaters, then the PF is 1.0 so W = VA
If the load is inductive in nature, like motors, electronic power supplies etc., then you need to know the Power Factor to determine VA, no way around it. You can make a SWAG at it by ASSuming the PF is .80, but that's all it is, a SWAG. If you want an extra conservative VA value from only knowing watts, you can use .70 PF. It's very rare to see loads with lower than a .70 PF.
So for example lets say you have a 4kW load and you want to know the kVA. If you don't know the PF of the load and want to be conservative, you take 4kW/.7 = 5.71kVA. it will likely be less, but this may be the only way to be safe at guessing.