By the UK Generator Guide — Home Petrol Generator Reviews & Advice Team · Updated May 2026 · Independent, reader-supported

What Size Petrol Generator Do I Need for My Home? (UK Wattage Guide)

Choosing the right petrol generator for your home comes down to one question: how many watts do you actually need? Buy too small and you'll either overload it or find it can't run the appliances you need. Buy too large and you're wasting money on fuel and storing a machine far heavier than necessary.

The answer depends on what you plan to power and whether you're looking to run items one at a time or simultaneously.

Running watts vs startup watts

This is the critical detail most people miss. Nearly every electrical appliance draws more power when it first switches on than it does when running normally.

Running watts (also called rated watts) is what the appliance consumes once it's operating steadily. Startup watts (inrush or surge watts) is the brief spike you get at the moment of switch-on, typically lasting just a few seconds.

A kettle rated at 2.8 kW might draw 3.2 kW for the first instant. A fridge might run at 150 W but need 800 W to kick the compressor over. If your generator's maximum output is only rated for running watts, you'll trip the breaker the moment you switch on a high-inrush device.

Generator specs always list both figures. You need to meet the startup requirements of your most power-hungry simultaneous loads, not just the running total.

Common UK appliances and their wattage

Here are the figures that matter for typical UK home appliances:

Kitchen appliances:

• Electric kettle: 2,500–3,000 W running (no meaningful startup surge)
• Microwave: 800–1,200 W running; 1,200–1,500 W startup
• Oven: 2,000–3,000 W running (varies by model)
• Electric cooker: 7,000+ W (rarely run from a generator)
• Dishwasher: 1,800–2,400 W running; 2,000–3,000 W startup
• Washing machine: 1,500–2,500 W running; 2,500–3,500 W startup
• Tumble dryer: 2,000–5,000 W running (very high demand)
• Fridge: 150–400 W running; 600–1,000 W startup

Heating and cooling:

• Electric heater (2 kW fan heater): 2,000 W running; 2,200 W startup
• Air conditioning unit: 1,500–3,500 W running; 3,000–5,000 W startup
• Immersion heater: 2,000–3,000 W running

Other appliances:

• Television: 100–300 W running
• Computer and monitor: 300–500 W running
• LED lighting (whole house, typical): 500 W total
• Boiler (electric): 2,000–3,000 W running; 3,000–4,000 W startup
• Sump pump: 800–1,200 W running; 1,500–2,500 W startup
• Welder (small): 3,000–5,000 W
• Power tools (circular saw, angle grinder): 1,000–2,500 W running

These are realistic UK figures. Actual consumption varies by model and age—older appliances tend to draw more.

Calculating what you actually need

Start by listing the appliances you genuinely need to power simultaneously in a real outage scenario. Don't fantasise about running your tumble dryer, electric cooker, and kettle at the same time on a small generator. Think practically.

For most UK households, realistic scenarios include:

• Fridge, some lighting, and a laptop
• Boiler, heating, some lights, and a kettle
• Sump pump, essential lights, and a few sockets

Add up the running watts for all items you'll use together, then check the startup watts of the single item with the highest inrush demand. Your generator needs to exceed both figures.

Example scenario: You want to run a fridge (400 W running, 900 W startup), boiler (2,500 W running, 3,500 W startup), four lights (500 W total), and a microwave (1,000 W running, 1,400 W startup).

Total running: 400 + 2,500 + 500 + 1,000 = 4,400 W Highest startup: 3,500 W (boiler)

You'd need a generator rated for at least 3,500 W startup and 4,400 W running capacity. A 5 kW unit would handle this comfortably.

Oversizing is practical, not wasteful

A 3 kW generator can theoretically power items totalling 3,000 W, but it's running at maximum capacity with no headroom. Equipment degrades faster under sustained full load, and you can't add a single device without overload risk.

Aim to size your generator so that your typical load sits at 60–75% of its maximum capacity. This gives you:

• Headroom for appliances that draw more than spec
• Room to add devices without overloading
• Better fuel economy (generators are less efficient at full throttle)
• Longer engine life

In practical terms, if you've calculated 3 kW of simultaneous demand, a 5 kW generator is sensible, not excessive. You'll use less fuel overall because the engine works at a more efficient operating point.

Generator types and real-world considerations

Portable open-frame petrol generators are cheaper upfront but loud (80–90 dB) and offer no weather protection. Inverter generators are quieter, more fuel-efficient, and safe for electronics, but more expensive. Larger enclosed units are quieter still but cost significantly more and take up garden space.

Starting wattage matters most on the most demanding outage scenario you'll realistically face. If you're mainly concerned about powering essential items during a winter power cut, running a boiler and fridge, 3–5 kW covers most UK homes. If you want to maintain near-normal living standards, 5–7 kW gives you much more flexibility.

For detailed comparisons of specific 3 kW and 5 kW models suited to UK homes, check our roundup articles on those sizes separately.

The key principle: calculate honestly, size generously, and you'll have a generator that actually works when you need it.