All calculators

Ten calculators in three groups. Below each result, the page shows the formula, the code table it comes from and a worked example.

Backup power

Generators, portable power stations and home batteries: how big, how long, how much fuel.

• Generator size calculatorAdd up running and starting watts for the appliances you want to keep on.
• Power station runtime calculatorHours of runtime from a portable power station or battery for any load.
• Home battery backup calculatorkWh and number of battery units to ride out an outage.
• Generator fuel consumption calculatorGallons or cubic feet per hour, per day and per tank.
• Amp hours to watt hours calculatorConvert battery Ah to Wh (and back) at 12 V, 24 V, 48 V or any voltage.
• Solar panel calculatorHow many solar panels and kW cover your use, with NREL production for your state.

Wiring

Wire gauge, voltage drop and breakers by the NEC tables, including the cable-type rules most charts skip.

• Wire size calculatorAWG for a circuit by amps, cable type and run length, per NEC 310.16.
• Voltage drop calculatorVolts and percent lost over a run, and the gauge that keeps it under 3%.
• Breaker size calculatorBreaker amps from watts or amps, with the 125% continuous-load rule.
• EV charger circuit calculatorBreaker, wire and charging speed for a Level 2 charger.

Energy use and cost

Watts, amps and what an appliance costs to run at your state’s actual electricity price.

• Electricity cost calculator for appliancesWhat any appliance costs per hour, month and year at your state’s price.
• Watts to amps calculatorConvert watts and amps at any voltage, with power factor.
• Amps to watts calculatorWatts from amps and volts, and how many watts each breaker carries.
• Electricity bill calculatorYour monthly bill from kWh, or your real price per kWh from your bill.