Power, Backup Generator, Battery Runtime & Extension Cord Calculators
Power calculators need to account for more than the number on the box. Startup surge, running watts, battery capacity, inverter losses, voltage drop, and cord size all matter.
Best starting point
Use this page as the project path. Start with the main calculator, read the short guide if you need context, then print the matching checklist before comparing quotes or buying materials.
Before buying a generator
- Add startup surge for pumps, compressors, and AC equipment.
- Verify nameplate ratings before sizing hardwired backup.
- Use proper transfer equipment for home backup.
Before buying a battery
- Use watt-hours when possible.
- Account for inverter losses and usable capacity.
- Check output watt limits, not only runtime.
Before using an extension cord
- Enter one-way length.
- Use the actual amp draw.
- Use heavier cord for long runs and motor loads.
Calculators in this cluster
Use these tools together instead of treating each estimate as a standalone number.
Home Backup Generator Size Calculator
Estimate generator size for outage essentials and motor-starting loads.
Open tool → CalculatorCamping & RV Generator Size Calculator
Estimate RV, camping, cabin, and outdoor generator wattage.
Open tool → CalculatorPortable Power Station Runtime Calculator
Estimate runtime from power station watt-hours and selected device loads.
Open tool → Popular planning toolBattery Runtime Calculator
Estimate runtime from watt-hours, amp-hours, voltage, and continuous watts.
Open tool → CalculatorExtension Cord Voltage Drop Calculator
Check voltage drop from one-way cord length, amps, volts, and AWG.
Open tool →Helpful guides
These explain the assumptions behind the calculators and the mistakes that usually cause bad estimates.
Backup Generator Size Calculator Guide
Size essential backup loads, standby generator planning ranges, startup surge, well pumps, sump pumps, and central AC cautiously.
Read guide → GuideExtension Cord Gauge Calculator Guide
Choose extension cord gauge from cord length, amps, voltage, AWG, and voltage drop for tools, generators, chargers, and motor loads.
Read guide → GuideBattery Runtime Calculator Guide
Understand watt-hours, amp-hours, 12V batteries, inverter loss, and device watts.
Read guide →Quote and planning tools
Printable tools make the estimate more useful when you are preparing for a real project or comparing contractor quotes.
How this helps with real projects
This hub connects the calculator, guide, cost estimator, and printable checklist for one topic. That makes it easier to move from a quick estimate to a project-ready plan without hunting through unrelated pages.