How to Calculate Generator Size for a Tiny House (7 Steps)

You calculate generator size for a tiny house by adding your running watts, your single biggest startup surge and a 20% safety margin. Most tiny houses land between 3,000 and 4,500 watts enough for lights, a fridge, a water pump and one mini split AC at a time.

How to Calculate Generator Size for a Tiny House: Step by Step

Follow these seven steps to calculate generator size for a tiny house before you buy anything.

1. List every appliance: Write down what you'll actually run off the generator and its running watts from the nameplate.
2. Flag the motors: Anything with a compressor or pump, AC, fridge, water pump, needs 2 to 3 times its running watts for startup surge.
3. Pick a realistic scenario: Decide what actually runs together not the AC, microwave and water heater all at once.
4. Add running plus one surge: Total your scenario's running watts, then add only your single highest surge figure.
5. Add a 20% margin: Pad that total so the generator isn't running flat out all day.
6. Match the continuous rating: Convert watts to kW and buy based on the generator's continuous rating not its peak number.
7. Check the inlet: Confirm the generator's outlet matches your tiny house's 30A or 50A inlet before you buy.

The Mistake That Costs You a Fried Compressor

Most people size a generator off running watts alone and stop there. That's the mistake: a 13,500 BTU tiny house style AC unit needs only 1,300 to 1,800 running watts. 

Its startup surge can hit 2,800 to 3,500 watts roughly double the running load (Erayak Power, 2026). Skip that number and the compressor pulls more current than the generator can supply. Worst case? A fried compressor and a dead AC unit.

Bottom Line

Round up, always. Undersizing kills more generators than any other mistake. Calculate generator size for a tiny house with running watts, one surge figure and a 20% margin, then buy on continuous rating not peak.

The tiny home electrical and plumbing load calculator takes your running plus surge plus 20% total and turns it into the exact peak amp draw you need to match a generator and inlet size. Find your exact power and pipe sizing

Other Common Tiny House Questions: How to Reduce Electrical Load in a Tiny House: 6 Step Guide