GENERATOR CALCULATOR

Find Out What Generator You Need for Your Power Requirements

Generator Selection & Usage Guide
Recommended Generators
Generator Selection & Usage Guide

Choosing the right size generator saves you money and avoids the frustration of tripping breakers or underpowering your tools. Too small and it won't handle the load. Too large and you're paying for capacity you'll never use. Our generator sizing calculator helps you work out exactly how much power you need. Select your use case below, add the appliances or equipment you want to run, and get an instant recommendation matched to generators in our range. Whether you need backup power for your home during outages, a portable unit for the job site, or a standby generator for your off grid setup, this tool gives you a clear answer in under a minute.

Running Watts vs Starting Watts

Every motor driven appliance draws more power when it first starts up than when it runs continuously. A fridge compressor might run at 150W but spike to 600W on startup. An air compressor rated at 1,500W can draw 4,500W for the first few seconds. The calculator factors in these starting loads automatically, so the generator it recommends will handle both the startup spike and the continuous running load without tripping the overload protection.

Inverter vs Conventional Generators

Inverter generators produce clean, stable power (pure sine wave) that's safe for laptops, phones, medical equipment, and sensitive electronics. Conventional generators deliver reliable, cost effective power for tools, pumps, and lighting. If you're powering a mix of both, an inverter generator is the safer choice. The calculator recommends both types where appropriate based on your use case.

Common NZ Power Requirements

Typical home backup during a power outage (fridge, lights, WiFi router, phone chargers): approximately 2,000W running. Small workshop (angle grinder, drop saw, lights): approximately 3,000 to 5,000W. Dairy shed or large workshop with a welder: 8,000 to 15,000W or more. If you're not sure where your setup falls, the calculator will work it out for you.

Need Help Choosing?

Our team has 40 years of combined experience in generator applications including mains failure, remote start, solar backup, and custom built setups. If the calculator gives you a result and you're still not sure which generator is the right fit, call us on 0800 GENERATOR or submit a Quick Enquiry on any product page and we'll recommend the best option for your situation.

Frequently asked questions

Using the tool

How does the generator calculator work?
Choose what you need the generator for, Home, Caravan, Farm, Business or Something Else, then add the appliances you want to run at the same time. Only add what will be on at once, not everything you own. The calculator allows for the starting surge of motors and recommends generators from our range that can handle the load.
What’s the difference between running watts and starting watts?
Running watts are what an appliance draws once it’s going. Starting watts are the short spike when a motor starts up, which can be several times higher. Fridges, freezers, pumps, compressors and power tools all have a starting surge, and it often decides the generator size.
Do I need an inverter generator or a conventional one?
Choose an inverter if you’re powering laptops, TVs, phones or other sensitive electronics, or if noise matters, for example at a campground. Conventional generators are cost effective for tools, pumps and lighting. If you’re running a mix, an inverter is the safer choice.
I’m still not sure which generator is right. Who can I talk to?
Our team has 40 years of combined experience with generators, from home backup to mains failure and remote start setups. Call us on 0800 GENERATOR or send a Quick Enquiry from any product page, and we’ll recommend the best option for your situation.

Sizing questions

What size generator do I need?
It depends on what you want to run at the same time, not on the size of your home or site. Add up the running watts of everything you need on at once, then allow for the starting surge of the largest motor. If your result sits close to the limit of a recommended size, step up to the next one.