Choosing the right inverter size is one of the most important decisions when building a backup power, RV, solar, off-grid, or battery energy system.
So, what size inverter do you need?
The answer depends on more than the wattage of a single appliance. You need to consider the total continuous load, startup surge, appliances that may run at the same time, battery voltage, and additional capacity for future loads.
As a simple starting point:
Required inverter size = maximum simultaneous running load + sufficient surge capacity
For example, if the appliances you expect to operate at the same time consume 1,800W, a 2,000W inverter may be close to the limit. A 3,000W inverter may provide more practical operating headroom, depending on the loads and their startup requirements.
Use the guide below to calculate the inverter size for your application.
Quick Answer: What Size Inverter Do I Need?
For many applications, you can estimate inverter size using this basic process:
- List the appliances you want to power.
- Find the running watts of each appliance.
- Add the appliances that may operate simultaneously.
- Identify appliances with high startup or surge requirements.
- Check the inverter’s continuous and peak power ratings.
- Make sure the battery can supply the required DC power.
- Select the appropriate battery voltage: 12V, 24V or 48V.
Victron’s current inverter sizing guidance similarly emphasizes continuous load, combined loads, startup surge, temperature derating, battery voltage and battery capability when selecting an inverter.
Simple example
Suppose you want to run:
| Appliance | Running Power |
|---|---|
| Refrigerator | 200W |
| TV | 120W |
| Laptop | 100W |
| Lights | 100W |
| Router | 20W |
| Total | 540W |
Your continuous load is approximately 540W.
However, the refrigerator may require substantially more power during startup. Therefore, choosing an inverter only slightly above 540W may not provide enough startup capability.
A 1000W pure sine wave inverter with appropriate surge capacity could be considered for this type of small system, subject to the actual appliance specifications.