What is the difference between watts and VA?

Watts measure real power consumed by the load. VA (volt-amperes) is apparent power, which is what the inverter must supply before the load's power factor converts it to useful work. For most resistive loads (heaters, lights) the ratio is close to 1:1. For motors and electronics it is typically 0.6–0.9, so the VA rating must be higher. This calculator uses a 0.8 power factor as a conservative default.

Why is a 1.25× safety margin applied?

Running all appliances simultaneously at rated wattage for extended periods stresses an inverter. The 25% headroom prevents thermal shutdown, extends component life, and leaves room for appliance wattage tolerance.

What about surge or startup watts?

Motor-driven appliances (fridges, pumps, air conditioners) draw 2–3× their running watts for a fraction of a second at startup. This calculator sizes for sustained running load. Check your inverter's surge rating separately — most inverters handle 200% surge for a few seconds, which covers most motors.

What common inverter sizes are available?

Standard commercial sizes are 600 W, 1000 W, 1500 W, 2000 W, 3000 W, 5000 W, and 6000 W. The calculator recommends the next size up from your calculated minimum so you always have headroom.

How do I use the daily Wh figure?

Daily watt-hours tell you how much energy storage (battery bank) or generation (generator runtime) you need each day. Use the Solar Battery Bank Size Calculator to convert Wh/day into the Ah capacity you need at your system voltage.

Inverter Size Calculator

Name: Inverter Size Calculator
Availability: InStock
Author: Nham Vu

Add your appliances, get the inverter size (watts and VA) you need for a solar or backup power system.

Appliance Load List

Appliance	Running Watts	Hours / Day	Wh / Day
Totals			—

Total Running Watts

—

Sum of all appliances

Min. Inverter (VA)

—

Running W ÷ 0.8 PF × 1.25

Recommended Size

—

Next standard inverter tier

Daily Energy Consumption

Use this to size a battery bank or calculate generator runtime

—

Common Inverter Sizes

Inverter (VA)	Typical Use Case	Max Running W (PF 0.8)

Summary

Add your appliances, get the inverter size (watts and VA) you need for a solar or backup power system.

How it works

Enter each appliance name, its running wattage, and how many hours per day it runs.
Add as many appliances as you need with the "Add Appliance" button.
The calculator sums running watts and applies a 1.25× safety factor.
Running watts are divided by a 0.8 power factor to get the minimum VA rating.
A recommended inverter size is selected from common commercial sizes (600 W – 6000 W).
Daily watt-hours are calculated so you can size a battery bank or generator.

Use cases

Size an inverter for an off-grid cabin or tiny home.
Plan a solar backup system for critical household loads.
Determine the inverter needed for an RV or van build.
Verify an existing inverter can handle a new appliance load.
Estimate daily energy draw to pair with a battery bank calculator.
Compare inverter costs by finding the exact commercial size tier needed.

Frequently Asked Questions

Last updated: 2026-07-01 · Reviewed by Nham Vu