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?
Pick what you need the generator for, then tick the appliances and tools you want to run at the same time. The calculator adds up the running watts, allows for the starting surge of the largest motor, and returns a minimum kVA figure along with the models in our range that meet it. It takes about a minute.
Which option should I choose?
Home covers backup power during an outage: fridge, freezer, lighting and often a water pump. Caravan covers travel and off grid use where quiet running matters. Farm is usually built around a pump or a shed. Business covers workshops, sites and commercial premises. Pick Something Else if none of these fit and you want to build your own list.

Sizing questions

Should I size for running watts or starting watts?
Both, but not by adding everything together. Total the running watts of everything you need on at once, then add the starting watts of the single largest motor only. Motors rarely start at the same instant, so adding every starting figure gives a number far larger than you need and costs you money.
Will a 5kVA generator run a house in NZ?
It will run the essentials in most homes: fridge, freezer, lighting, a television and a water pump, though not all at the moment the pump starts. It will not run electric hot water, an oven or a heat pump at the same time as everything else. For those you are looking at X kVA or more.