The RV generator sizing calculator adds up your appliance wattage requirements — including startup surge — to recommend the minimum generator capacity for your rig. Undersizing a generator causes overloads; oversizing wastes money and fuel.
Appliance Load List
How to Size an RV Generator
Generator sizing for an RV involves two numbers: running watts (continuous load) and startup surge (peak watts for a fraction of a second when a motor starts). Your generator must handle both.
Running vs Startup Watts
Air conditioners are the dominant load in most RVs. A 15,000 BTU roof AC draws about 1,500W running but surges to 3,000–3,500W on startup. A 13,500 BTU unit draws roughly 1,200W running with a 2,800W startup surge. Always size to the surge, not just the running load.
Generator Sizing Rule
Add up all running watts for appliances you'll use simultaneously. Then take the highest single startup surge and add the remaining running watts — this is your peak demand. Choose a generator rated for 120% of peak demand to give comfortable headroom and extend generator life.
Inverter vs Standard Generators
Inverter generators produce clean power safe for sensitive electronics (TVs, laptops, CPAP machines). They're also quieter and more fuel-efficient at light loads. Standard generators cost less but produce rougher power. For RV use, inverter generators are strongly recommended despite the higher cost.
Frequently Asked Questions
Is this RV generator sizing calculator free?
Yes, completely free with no signup or account needed.
Why does a generator need to handle startup surge?
Motors in air conditioners, refrigerators, and pumps draw 2-3x their running wattage for a fraction of a second on startup. A generator that can only handle running watts will trip its overload protection or stall when these appliances start. Size your generator to the highest startup surge you expect.
What size generator do I need to run a 15,000 BTU RV air conditioner?
A 15,000 BTU RV AC draws about 1,500W running and up to 3,500W on startup. A 3,500W generator is the minimum; a 4,000W unit gives comfortable headroom. Running two AC units requires at least 6,500-7,000W.
Is propane or gas generator better for an RV?
Gasoline generators are widely available and powerful. Propane generators are quieter, emit less exhaust, and fuel doesn't go stale. Many RVers with built-in generators use gasoline or diesel. Portable dual-fuel units give flexibility. Inverter generators (any fuel) are quieter and better for sensitive electronics.
What is an inverter generator and do I need one?
Inverter generators produce clean sine wave power suitable for computers, TVs, and other sensitive electronics. Standard generators produce rougher power that can damage electronics over time. For RV use with TVs, laptops, and modern appliances, an inverter generator is strongly recommended.