Off-Grid Power Sizing

Inverter Sizing Calculator

RV electrical build, off-grid van conversion, emergency home backup inverter selection. Interactive appliance selector that computes total continuous load + largest inductive motor surge to recommend minimum Pure Sine Wave inverter size.

Inverter Sizing Calculator
Watts
Watts
Calculated Result
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Instant Calculation
Auxiliary Value
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Engineering Output
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Step-by-Step Derivation ▼ Show Steps
Governing Formula Verified Physics
Continuous Watts = Running Watts × 1.25  |  Surge Watts = Continuous + Motor Surge

Calculations adhere to standard electrical equations and National Electrical Code guidelines.

Engineering Principles & Calculations

This calculator uses the exact mathematical relationships between List of Appliances (Fridge, TV, Microwave, Tools, Lights) with Running & Starting Watts to determine Recommended Inverter Continuous Watts, Surge Rating (W), Recommended DC Cable Gauge. In practical applications, electrical systems must account for safety derating factors, nominal vs actual voltages, and conductor resistance losses.

Interactive appliance selector that computes total continuous load + largest inductive motor surge to recommend minimum Pure Sine Wave inverter size.

Typical Application & Best Practices

RV electrical build, off-grid van conversion, emergency home backup inverter selection.

Reference Matrix

Inverter Sizing Calculator Benchmark Lookup Table

Typical Household LoadRunning WattsStarting SurgeRecommended Inverter
Laptops, Lights, Starlink250 W350 W600 W Pure Sine
Refrigerator + TV + Fans600 W1,800 W1,500 W / 3,000 W Surge
Microwave + Coffee Maker1,500 W2,200 W2,000 W / 4,000 W Surge
Well Pump / Power Tools1,800 W4,500 W3,000 W / 6,000 W Surge
RV Air Conditioner (15k BTU)1,800 W3,600 W3,000 W / Soft-Start
Whole Off-Grid Cabin3,500 W7,000 W5,000 W / 10 kW Surge
FAQ

Frequently Asked Questions

What size inverter do I need? +
Add the running watts of all devices you intend to power simultaneously, multiply by 1.25 for a safety buffer, and ensure the inverter's surge rating can handle the largest electric motor starting current.
What is the difference between Pure Sine Wave and Modified Sine Wave? +
Pure Sine Wave produces clean AC identical to utility grid power, required for modern refrigerators, laptops, CPAP machines, and audio equipment. Modified sine wave creates harmonic noise and overheats motors.
Why does an inverter need a starting surge rating? +
Induction motors (compressors in fridges, air conditioners, and pumps) require 3 to 6 times their running wattage for 1-2 seconds during startup.

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