Before you buy, you need to know your “Concurrent Load”—this is the total power used if everything is turned on at the same time. Follow this simple 3-step calculation:
Step 1: The Essentials List
List every appliance you want to run during load-shedding and find its average wattage (usually found on a sticker on the back of the device).
| Appliance | Average Wattage |
| LED Light Bulb (x10) | 100W |
| Wi-Fi Router | 20W |
| LED TV (55″) | 150W |
| Laptop | 60W |
| Fridge/Freezer | 200W – 400W |
| Total Essentials | ± 730W |
Step 2: The “Surge” Appliances
These are the items that make a 3kW inverter struggle but are fine for a 5kW or 8kW.
- Microwave: 1,200W
- Kettle: 2,000W – 3,000W
- Washing Machine: 500W (Cold) / 2,500W (Hot)
- Hairdryer: 1,800W
Step 3: The Math
Add your Total Essentials to the largest single appliance you might use at the same time.
Example:
Essentials (730W) + Microwave (1,200W) = 1,930W.
A 3kW Inverter would handle this easily.
Essentials (730W) + Kettle (3,000W) = 3,730W.
You would need a 5kW Inverter to avoid a trip.
Important: The “Safety Margin” Rule
In South Africa’s heat, we recommend the 80% Rule. Never run your inverter at 100% capacity for long periods.
- If your load is 2,400W, don’t get a 3kW (which is 3,000W). Move up to a 5kW to give the system “breathing room” and ensure a longer lifespan.
2 responses to “DIY Load Calculator: What Size Inverter Do You Really Need?”
Thank you
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