I have a plug in meter that reads volts and line frequency. It also allows the plug in of a device and reads out the watts and voltamps of the device. What's the difference between watts and voltamps. I get a different reading.

M4-AK

For a purely resistive load, the two (W & VA) will be equal.

For reactive loads (capacitive or inductive), current is not in phase with voltage and you will get different readings.

So when determining how much capacity I need for an inverter or gas generator, should I go with the higher number to be safe?

M4-AK

Amps is a scalar quantity.  The apparent power used by any inductive-capacitive-resistive load is a combination of the actual power (current in phase with the voltage) and the reactive power (current at 90º to the voltage).  This is a vector equation.  Think of it as a right triangle, with the actual power being the long leg, the reactive power being the short leg, and the apparent power being the hypotenuse.  You have to size all of your equipment for the apparent power, because even if it's not all doing work, that amperage is flowing through your hardware.

So when determining how much capacity I need for an inverter or gas generator, should I go with the higher number to be safe?

Short answer:  YES.

This isn't a good way of doing the math. But I find it works close enough for up 3000VA when I am calculating capacity needs for UPSes (battery backup).

The wattage rating is roughly 2/3 the volt-amp rating on the UPS. When dealing with computers and UPSes this works well enough.

Heres a link on the subject that won't help much:
en.wikipedia.org/wiki/Volt-amp

-Foxxz

You shure u don't want a frequancy generatur?

Quoted: You shure u don't want a frequancy generatur?

I do

-Foxxz

Quoted: You shure u don't want a frequancy generatur?

25 hZ d.c.