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Know the load.
Size it right.
Then call the pro.

Electrical calculators for planning a project, checking a circuit, or sizing a generator before you buy.

Estimates only. Electrical code varies by city, county, and state. Check your local code and use a licensed electrician for any wiring work. Read the full disclaimer.
Electrical

Electrical Calculators

Electricity Cost Calculator

See what an appliance costs to run per day, month, and year.

Job: Electrical
How it works: watts ÷ 1,000 × hours = kWh per day. kWh × your rate = cost. Example: a 1,500 W space heater running 8 hours a day uses 12 kWh, about $1.80 a day at $0.15/kWh, or roughly $54 a month.
⚠️ Estimates only. Actual use varies with thermostats, cycling, and your plan's fees.

Watts, Amps & Volts Calculator

Convert between watts and amps for any device, like "how many amps is a 1,500 W heater?"

Job: Electrical
How it works: watts = volts × amps, so amps = watts ÷ volts. Example: a 1,500 W heater on a 120 V outlet draws 12.5 amps. That is fine on a 15 amp circuit by itself, but not with much else plugged in.
⚠️ Estimates only. Motors can draw more when starting than their label shows.

Circuit Load Calculator

Add up what's plugged into one circuit and see if the breaker can handle it.

Job: Electrical
How it works: total watts ÷ volts = amps on the circuit. Things that run for 3 hours or more (heaters, chargers) should stay under 80% of the breaker, so a 20 amp circuit tops out at 16 amps of steady load. Example: a 1,500 W heater plus a 100 W TV and a 60 W lamp is 1,660 W, or 13.8 amps, which fits a 20 amp circuit but is over the steady-use limit on a 15 amp circuit.
⚠️ Estimates only. If a breaker trips often, have an electrician check the circuit. Never swap in a bigger breaker without checking the wire size.

Wire Size & Voltage Drop Calculator

Check a wire run to a shed, garage, or RV hookup, and find the smallest wire that keeps voltage drop under 3%.

Job: Electrical
How it works: voltage drop = 2 × distance × wire resistance × amps. The suggested size is the smallest wire rated for your amps (using the common 60°C table values for home wiring) that also keeps the drop at 3% or less. Example: 20 amps at 120 V over 100 feet of 12 AWG copper drops about 7.7 volts (6.4%), so 8 AWG is the smallest size that stays under 3%.
⚠️ Estimates only. Wire size also depends on insulation type, temperature, conduit fill, and your local code. Have an electrician confirm before you buy.

Generator Size Calculator

Check off what you want to run during an outage and see how big a generator you need.

Job: Electrical
How it works: add up the running watts of everything on at once, then add the biggest extra jump from a motor starting up (only one usually starts at a time). The suggested size adds about 20% headroom. Example: a fridge, sump pump, lights, TV, and Wi-Fi run about 2,100 W, and the fridge's startup needs about 1,500 W more, so a generator rated around 2,600 running and 4,400 starting watts fits.
⚠️ Watt values are typical. Check each appliance's label. Never plug a generator into a wall outlet. Use a transfer switch or interlock installed by a licensed electrician, and run generators outdoors, far from windows.

Electrical Calculator Disclaimer

The electrical calculators on CalcProject.org provide general estimates for planning and educational purposes only. Results are based on common standards and simplified formulas and may not account for every factor in your situation, such as wire type, temperature, conduit fill, or load type.

Electrical code requirements vary by city, county, and state, and local codes may differ from national standards like the National Electrical Code (NEC). Always check with your local building department and consult a licensed electrician before doing any electrical work.

Working with electricity can cause serious injury, death, or fire. CalcProject.org is not responsible for any damage, injury, or loss resulting from the use of these calculators.