⚡ Generator Load Size Calculator

🔧 Professional generator sizing tool — accurately estimate continuous & starting (surge) power requirements for homes, job sites, or events. Based on real-world appliance data, altitude derating, and safety margins (NEC & international best practices). Adjust loads, add custom devices, and get clear capacity recommendations in kW/kVA. Works worldwide (120V/230V/240V systems). Use the table below to add all appliances you want to power.
📋 Electrical Loads (Running / Starting)
ApplianceRunning (W)Starting (W)QtyTotal Run (W)
💡 Starting surge: Motor-driven devices (AC, fridge, pump) require 3–6x running watts for brief moments. Generator must handle the largest surge increment + total running load.
📊 Load Analysis & Generator Requirements
Above 3000ft, engine output drops ~3.5% per 1000ft. Increases required generator size.
Recommended 20–30% extra capacity for headroom and longevity.
PF 0.8 typical for motors; generator kVA = kW ÷ PF. Use 1.0 for resistive loads.
📐 Advanced Generator Sizing Results
⚙️ Total Running Load
0 W
Continuous power needed
🚀 Peak Surge Requirement
0 W
Starting + running sum (largest surge)
🔄 Recommended Gen. Running (kW)
0.00 kW
incl. altitude + margin
⚠️ Recommended Gen. Peak (kW)
0.00 kW
must cover surge + derating
📐 Apparent Power (kVA) @ PF
0.00 kVA
Generator kVA rating (continuous)
🇺🇸 USA standards & world guidance
✔ NEC 702 & 445: running load ≤90% of generator rating recommended.
✔ Starting surge: largest motor LRA + sum others.
✔ Altitude derate: subtract 3% per 1000ft > 1000ft (apply to gen capacity).
🌎 Global best practice
✔ Running Watts sum (all devices)
✔ Peak = Running sum + Max(Starting – Running) per device
✔ Add 20% safety factor for resistive/inductive mix.
⚙️ Adjustable factors
• Altitude (oxygen reduction) → requires larger generator
• Safety margin prevents overload
• Power factor (PF) for true kVA rating

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