Size a Generator for Cabin, RV, and Home-Backup Surge
Updated 2026-10-21 · Published by Charland & Co. · Based on published specs; we have not tested the products discussed.
Quick answer: A cabin with 800 W running (including a fridge at 150 W running) and a fridge that needs 1,200 W to start will need a generator with at least 1,850 W surge capacity. Continuous power must cover all running devices at once, so a 1,000 W continuous generator would work if the total running load is under 1,000 W.
Continuous Watts Versus Surge Watts
When sizing a generator, it's important to understand the difference between continuous watts and surge watts.
- Continuous watts are the amount of power a generator can provide continuously. This is the power you need to run all your devices at the same time.
- Surge watts are the extra power a generator can provide for a short time (usually a few seconds) to start devices that require more power to turn on, like a fridge or a well pump.
The Surge Formula Step by Step
To calculate the surge watts your generator needs, use this formula:
Surge Watts = (Total Running Watts) - (Largest Running Watt Device) + (Largest Starting Watt Device)
Let's break this down with an example:
- Total Running Watts = 800 W (this includes all devices running at the same time, like lights, a TV, a small fan, and a fridge running at 150 W)
- Largest Running Watt Device = 150 W (the fridge when it's running)
- Largest Starting Watt Device = 1,200 W (the fridge when it starts)
Surge Watts = 800 - 150 + 1,200 = 1,850 W
So, in this example, you would need a generator with at least 1,850 W surge capacity.
Typical Starting Loads for Fridges and Pumps
Here are some typical starting loads for common devices:
- Fridge: 1,200-1,500 W starting, 100-200 W running
- Well Pump: 1,000-2,000 W starting, 200-500 W running
- Air Conditioner: 1,500-2,500 W starting, 500-1,000 W running
- Microwave: 1,000-1,500 W starting, 700-1,200 W running
- Electric Heater: 1,500-2,000 W starting, 1,000-1,500 W running
These numbers can vary depending on the device and its age. Always check the manufacturer's specifications for the most accurate information.
Matching Generator Size to Power-Station Hybrid Use
If you're using a generator and a power station together, you can reduce the size of the generator you need. The power station can handle the continuous load, while the generator handles the surge.
For example, if your total running load is 800 W and your largest starting load is 1,200 W, you could use a power station with at least 800 W continuous output and a generator with at least 1,200 W surge capacity.
This hybrid approach can be more cost-effective and efficient, especially for weekend use where you don't need continuous power for long periods.
Fuel Use on Weekend Trips
Generators typically run on fuel like gasoline, propane, or diesel. Fuel use depends on the generator's size and the length of time it runs.
For example, a small 1,000 W generator might use about 0.5 gallons of gasoline per hour. If you're using it for 4 hours on a weekend trip, that's 2 gallons of gasoline.
Always check the manufacturer's specifications for fuel consumption rates. You can also use our free calculator to estimate fuel use based on your generator's size and runtime.
Noise and Placement Considerations
Generators can be noisy, especially when they're running at full capacity. To minimize noise, choose a generator with a low decibel rating and place it as far away from your cabin or RV as possible.
- Placement: Keep the generator at least 20 feet away from your cabin or RV and away from doors, windows, and vents.
- Noise: Look for generators with inverter technology or quiet mode for reduced noise levels.
When a Generator Is Simpler Than Pure Solar
While solar power is a great option for off-grid living, it may not always be the best choice for weekend trips or emergency backup. Here are a few reasons why a generator might be simpler:
- Quick Setup: Generators are easy to set up and can be used immediately, whereas solar systems require installation and setup time.
- No Sunlight Required: Generators can be used at any time of day, while solar systems depend on sunlight.
- Higher Power Output: Generators can provide more power for high-wattage devices like air conditioners or electric heaters.
However, if you're planning to use your power system for extended periods or in remote locations, a solar-powered system might be more cost-effective and environmentally friendly.
Worked Example 1
Example: Sizing a Generator for a Weekend Cabin
Scenario: You're planning a weekend trip to a cabin and need to size a generator for your power needs.
Step 1: List Your Devices and Their Power Requirements
| Device | Running Watts | Starting Watts |
|---|---|---|
| Lights | 100 W | - |
| TV | 100 W | - |
| Fan | 50 W | - |
| Fridge | 150 W | 1,200 W |
| Microwave | 1,200 W | 1,500 W |
Step 2: Calculate Total Running Watts
Total Running Watts = 100 + 100 + 50 + 150 + 1,200 = 1,600 W
Step 3: Calculate Surge Watts
Surge Watts = (Total Running Watts) - (Largest Running Watt Device) + (Largest Starting Watt Device)
Surge Watts = 1,600 - 1,200 + 1,500 = 1,900 W
Step 4: Choose a Generator
Based on the calculations, you would need a generator with at least 1,900 W surge capacity and 1,600 W continuous output.
You can use our free calculator to input your own devices and get a more accurate estimate.
Worked Example 2
Example: Sizing a Generator for an RV with a Well Pump
Scenario: You're planning an RV trip and need to size a generator for your power needs. Your main devices are:
| Device | Running Watts | Starting Watts |
|---|---|---|
| Lights | 100 W | - |
| TV | 100 W | - |
| Fan | 50 W | - |
| Fridge | 150 W | 1,200 W |
| Well Pump | 300 W | 2,000 W |
Step 1: Calculate Total Running Watts
Total Running Watts = 100 + 100 + 50 + 150 + 300 = 700 W
Step 2: Calculate Surge Watts
Surge Watts = (Total Running Watts) - (Largest Running Watt Device) + (Largest Starting Watt Device)
Surge Watts = 700 - 300 + 2,000 = 2,400 W
Step 3: Choose a Generator
Based on the calculations, you would need a generator with at least 2,400 W surge capacity and 700 W continuous output.
This example shows how the surge watt requirement increases significantly when a high-starting-load device like a well pump is involved.
Step-by-Step How to Size a Generator
Here's a step-by-step guide to help you size a generator for your weekend cabin, RV, or home backup:
- List All Devices: Make a list of all the devices you plan to use, including their running watts and starting watts.
- Calculate Total Running Watts: Add up the running watts of all devices that will be on at the same time.
- Identify the Largest Running Watt Device: This is the device that uses the most power while running.
- Identify the Largest Starting Watt Device: This is the device that uses the most power when it starts.
- Calculate Surge Watts: Use the formula:
Surge Watts = (Total Running Watts) - (Largest Running Watt Device) + (Largest Starting Watt Device)
- Choose a Generator: Select a generator with at least the calculated surge watts and continuous watts equal to or greater than your total running watts.
Common Mistakes to Avoid
- Ignoring Surge Watts: Many people only consider continuous watts and forget about the surge watts needed to start devices like fridges or pumps.
- Underestimating Total Running Watts: Failing to account for all devices that will be on at the same time can lead to an undersized generator.
- Not Checking Device Specifications: Always verify the starting and running watts of your devices from the manufacturer or a reliable source.
- Overlooking Generator Size: Choosing a generator that is too small can result in it not starting your devices or overheating.
FAQ
How do I find starting watts for a fridge?
To find the starting watts for a fridge, check the manufacturer's specifications or look for a label on the fridge that lists the starting watts. If you can't find this information, you can use a watt meter to measure the power consumption when the fridge starts.
Can a 2,000 W generator handle a cabin fridge start?
Yes, a 2,000 W generator can handle a cabin fridge start if the fridge requires 1,200 W to start. However, you should also ensure that the continuous power of the generator is sufficient to run all your devices at the same time.
Should I size for the largest single start or everything at once?
You should size your generator for both the largest single start and everything running at once. This ensures that your generator can handle both the surge and the continuous load.
What if I have multiple devices that start at the same time?
If you have multiple devices that start at the same time, you should add up their starting watts and use that number in your surge watts calculation. This will give you a more accurate estimate of the generator size you need.
How do I know if my generator is too small?
If your generator is too small, it may not start your devices or may overheat and shut down. You can test your generator by connecting it to your devices and checking if it can start and run them without any issues.
Related Pages
- p01 / How to Size Off-Grid Power for a Weekend
- p03 / Build an Accurate Weekend Load List for Cabins, RVs, and Camps
- p10 / Worked Load and Capacity Example for a Typical Weekend Cabin
- p14 / Portable Power Station Versus Gas Generator for Weekend Cabins
- p25 / Solar-Only Weekend Systems Versus Solar-Plus-Generator Hybrids
Sources to Cite
- Honda EU2200i specifications (example running/max watts and run time per tank): https://powerequipment.honda.com/generators/models/eu2200i
- CPSC Portable Generator Safety Alert (placement, CO, backfeeding): https://www.cpsc.gov/s3fs-public/Portable-Generator-Safety-Alert-2017_5123.pdf
Who This Is Not For
This page is not for permanent off-grid living, commercial use, or large-scale power needs. It is specifically for weekend trips, RV boondocking, and home backup scenarios where a small to medium-sized generator is sufficient. If you need a larger, more powerful generator, consult a professional or refer to more advanced resources.