Electrical Calculators
Plan the numbers before you call an electrician, from what a device costs to run to how big a generator or wire run needs to be.
Electrical calculators
- Electricity Cost Calculator
Cost to run any device per hour, day, month and year from its watts and your state's price.
- EV Charging Cost Calculator
Home EV charging cost per mile and per year in your state, compared with a gas car.
- Generator Size Calculator
Running and starting watts for your outage loads and the generator size that covers them.
- Voltage Drop Calculator
Voltage drop for copper or aluminum wire and the smallest AWG size within your target percent.
What these tools are for
Electrical work is one of the few home projects where getting a number wrong can start a fire. These calculators are for planning and understanding. They tell you what an appliance costs to run, how much voltage a long wire run loses, how big a generator you need and what charging an electric car will cost. They don’t replace the electrical code or an electrician.
Electricity prices come from the U.S. Energy Information Administration’s latest averages for residential customers in each state, and you can override them with the rate on your bill.
What we don’t do
We don’t publish ampacity tables or tell you which breaker goes with which wire. Those rules are in the National Electrical Code as adopted in your area, and they depend on insulation type, temperature, bundling and installation method. Our voltage drop calculator uses physics only, and it says so in every result.
Any work inside a panel, on a service, or on a new circuit usually needs a permit and a licensed electrician.
Which electrical calculator do I need?
- “How much does it cost to run this?” The electricity cost calculator takes a device’s watts and hours of use and gives the kWh and the cost per hour, day, month and year at your state’s average price or your own rate.
- “What does it cost to charge an EV at home?” The EV charging cost calculator gives the cost per mile and per year, compares it with a gas car and estimates Level 1 and Level 2 charging times.
- “What size generator do I need?” The generator size calculator adds up the running and starting watts of the appliances you want to keep on in an outage, including the surge of pumps and compressors.
- “Is my wire big enough for a long run?” The voltage drop calculator works out the drop for copper or aluminum wire and the smallest AWG size that stays within your target percent.
Reading your electric bill
Most of these tools need a price per kilowatt-hour. The simplest way to find yours is to divide the total on a recent bill by the kWh used that month. That figure includes delivery charges and taxes, so it’s usually higher than the energy rate printed on the bill, and it’s the better number for estimating what an appliance really costs you. If you leave the rate blank, we use the latest EIA average for your state.