What Size Generator Do I Need?
Choosing the right generator size is the most important decision you'll make when buying portable power. Too small and you'll overload it. Too large and you'll waste money on fuel. This guide walks you through the maths step by step.
Step 1 — List Everything You Want to Power
Start by writing down every appliance or tool you plan to run. Common items and their approximate wattage:
| Appliance | Running Watts | Starting Watts |
|---|---|---|
| Refrigerator | 150–400W | 800–1,200W |
| Air conditioner (10,000 BTU) | 1,200W | 3,500W |
| Sump pump (1/2 HP) | 1,050W | 2,150W |
| Circular saw (7.25") | 1,400W | 2,800W |
| LED lighting (10 bulbs) | 100W | 100W |
| Phone/laptop chargers | 150W | 150W |
Step 2 — Add Up Running Watts, Then Find Your Peak
Add all running watts together. This is your base load. Then find the single appliance with the highest starting watts (motors need a surge to start) and add that surge on top.
Example: Fridge (400W) + lights (100W) + phone chargers (100W) = 600W running. The fridge has a 1,200W surge. So you need a generator that handles at least 1,800W peak. A 2,500W generator gives comfortable headroom.
General Size Guide by Use Case
- Camping / RV weekend trips: 2,000–3,500W inverter generator
- Home backup (essentials only): 5,000–8,000W
- Home backup (including AC): 10,000–14,000W
- Construction site (tools + lighting): 6,500–12,500W
- Events and markets: 4,400–8,000W
Dual Fuel Gives You More Flexibility
A dual-fuel generator (petrol + LPG propane) is worth the small premium. Propane stores indefinitely, so you always have backup fuel even if petrol stations are closed during an outage. Models like URBEXIA's 13,000W dual-fuel deliver full rated power on either fuel.
Don't Forget Continuous vs Peak Ratings
Generators are rated in two ways: peak watts (maximum surge for a few seconds) and running watts (sustained output). Always size based on running watts, then check the peak handles your biggest motor surge.
Frequently Asked Questions
Can I run my whole house on a portable generator?
Yes, but you'd need at least a 12,000–14,500W unit and a transfer switch to isolate your house circuits from the grid safely.
Is bigger always better with generators?
No. Running a large generator at 25% load wastes fuel and can cause carbon build-up (wet stacking). Aim to run at 50–80% of rated capacity.
How much fuel does a generator use per hour?
A 5,000W generator at 50% load uses approximately 1.5–2 litres of petrol per hour. A 10,000W unit at 50% uses around 3–3.5 litres.
