What is the difference between inverter VA and watts?

VA is what you buy, watts is what you use

VA (volt-amperes) is apparent power — the total the inverter must supply, including the part that sloshes back and forth in inductive loads without doing work. Watts is real power, the part that actually turns a fan. The ratio between them is the power factor, and Indian home inverters are conventionally rated at a power factor of about 0.8.

So a 900VA inverter delivers roughly 900 x 0.8 = 720W of usable continuous load. Buy on watts, convert to VA, then round up.

The sizing rule, in one line

Required VA = (your watts / 0.8) x 1.25. The 25% margin is not padding — it absorbs the fact that you will add an appliance next year, and that a battery ages into a higher effective load.

Then check surge separately. Motors spike at start-up, and a VA rating describes continuous output, not the two-second peak.

Bigger is not safer

An oversized inverter idles at a higher no-load draw, quietly eating battery through every outage, and costs more upfront. It also tempts you into connecting a load the battery cannot sustain — the inverter holds, and the battery dies in ninety minutes. Size the inverter to the load; size the battery to the outage.

Frequently asked questions

How many watts is a 900VA inverter?

About 720W of usable continuous load, because Indian home inverters are rated at a power factor of roughly 0.8. With a sensible 25% safety margin you would plan around 575W of steady load on a 900VA unit.

Why are inverters rated in VA and not watts?

Because inverters must supply apparent power, which includes the reactive component that inductive loads like fans and motors draw without converting it to work. VA describes what the inverter has to deliver; watts describes what the appliance consumes.

What power factor should I assume?

0.8 for a mixed Indian household load of fans, lights, TV and a fridge. Purely resistive loads approach 1.0, and heavy motor loads can sit lower.

Is a bigger inverter always better?

No. A larger inverter has a higher no-load idle draw, costs more, and encourages loads the battery cannot sustain. Size to the load plus a 25% margin.

Do I need pure sine wave?

For modern electronics, fridges, BLDC fans and anything with a motor controller, yes — modified sine wave causes humming, heating and in some cases outright refusal to run.