An RV inverter sizing calculator helps you determine the right inverter wattage for your RV, camper, or van by totaling your appliance running watts and surge watts. Enter the appliances you plan to run simultaneously, and get a recommended inverter size with pure sine wave vs modified sine wave guidance and wire gauge recommendations.
Add Appliances
Configuration
One-way distance from battery bank to inverter
Inverter Recommendation
Pure Sine vs Modified Sine Wave
Wire Gauge Recommendation
Load Breakdown
How to Use the RV Inverter Sizing Calculator
Choosing the right inverter for your RV, camper van, or travel trailer is essential for reliable off-grid power. An undersized inverter will trip its overload protection when you turn on a high-wattage appliance, while an oversized inverter wastes money and draws more idle power from your battery bank. This RV inverter sizing calculator walks you through the process step by step.
Step 1: Add Your Appliances
Start by clicking the preset buttons for common RV appliances like microwaves, coffee makers, hair dryers, and CPAP machines. Each preset includes accurate running and surge watt values. For appliances not on the list, use the custom entry form to add the name, running watts, and surge watts manually. Check the label on each appliance or its manual for wattage information.
Step 2: Mark Simultaneous Appliances
Toggle the simultaneous checkbox for each appliance you plan to run at the same time. The inverter only needs to handle your peak simultaneous load, not every appliance you own. For example, you probably will not run a hair dryer and microwave at the same time. Realistic simultaneous use is the key to accurate inverter sizing.
Step 3: Configure System Settings
Select your battery system voltage (12V, 24V, or 48V) and enter the cable length from your battery bank to the inverter location. Shorter cables reduce voltage drop and allow thinner wire gauges. Most RV installations use 12V systems with 3-6 feet of cable.
Step 4: Review Your Results
Click Calculate Inverter Size to see the recommended continuous wattage, surge rating, and inverter size. The calculator adds a 20% safety margin to your running watts and recommends the next standard inverter size up. You will also get pure sine wave vs modified sine wave guidance based on your specific appliance list, plus a wire gauge recommendation for safe installation.
Understanding Surge vs Running Watts
Motor-driven appliances like refrigerators, air compressors, and blenders draw 2-3 times their running wattage for a brief moment when starting up. Your inverter's surge rating must handle the total running load of all simultaneous appliances plus the highest single surge. This calculator automatically identifies the worst-case surge scenario and factors it into the recommendation.
FAQ
Is this RV inverter sizing calculator really free?
Yes, completely free with no signup required. All calculations run locally in your browser. Use it as many times as you need to compare inverter sizes for your RV, camper, or van.
Is my data safe when using this tool?
Absolutely. Everything runs entirely in your browser using JavaScript. No appliance data or personal information is sent to any server. You can even use it offline once the page loads.
What is the difference between running watts and surge watts?
Running watts (continuous watts) is the steady power an appliance draws during normal operation. Surge watts (startup watts) is the brief power spike when a motor or compressor starts up, which can be 2-3 times the running wattage. Your inverter must handle both.
Should I choose a pure sine wave or modified sine wave inverter?
Pure sine wave inverters produce clean power identical to household outlets and are required for sensitive electronics, CPAP machines, variable-speed motors, and medical devices. Modified sine wave inverters are cheaper and work fine for simple resistive loads like lights and basic chargers.
How much safety margin should I add when sizing an inverter?
Add a 20% safety margin above your total running watts. This accounts for power factor losses, inverter efficiency, and any appliances you may add in the future. For example, if your running total is 1500W, choose at least an 1800W inverter.
Can I run all my RV appliances at the same time?
Usually not. Most RV inverter setups cannot power every appliance simultaneously. The key is to identify which appliances run at the same time and size the inverter for that peak load. Stagger high-wattage items like microwaves and hair dryers.
What wire gauge do I need for my inverter?
Wire gauge depends on the inverter size and cable length between battery and inverter. A 1000W inverter at 12V draws about 83 amps, requiring thick cables. This calculator includes a wire gauge recommendation based on your inverter size and cable length.
How do I calculate surge watts for my inverter?
Your inverter's surge rating must handle all running loads plus the highest single appliance surge simultaneously. This calculator adds up your simultaneous running watts and adds the largest surge difference to determine the minimum surge rating needed.