All renewable energy calculators

24 free calculators, grouped by topic. New to the subject? Start with our guide to renewable energy.

Solar calculators

Size a solar array, find the best panel tilt, track the sun and plan an off-grid system.

Off-Grid Solar CalculatorOff-grid solar calculator: size your battery bank in kWh and Ah, solar array, charge controller and inverter from daily use and days of autonomy.Open calculator Solar Charge Controller CalculatorSolar charge controller calculator: find the amp rating, next standard size, string Voc with cold margin, and whether you need MPPT or PWM.Open calculator Solar Panel Angle CalculatorSolar panel angle calculator: get the best tilt for your latitude by month, plus year-round, summer and winter angles and which way to face panels.Open calculator Solar Panel CalculatorSolar panel calculator: find how many solar panels you need from your monthly kWh, peak sun hours and panel wattage, with system size and roof area.Open calculator Solar Position CalculatorSolar position calculator: find the sun's elevation, azimuth, zenith angle and day length for any latitude, date and solar time. Free sun angle tool.Open calculator

Wind calculators

Estimate how much power a wind turbine makes from its rotor size and your wind speed.

Wind Turbine CalculatorWind turbine calculator: estimate power output and yearly kWh from rotor diameter, wind speed and efficiency using the wind power formula P = ½ρAv³Cp.Open calculator

Electricity calculators

Work out kWh, running costs and your real price per kWh for any appliance or bill.

Carbon Footprint CalculatorFree carbon footprint calculator for home electricity, natural gas, driving and flights, using EPA eGRID2023 and EPA GHG Emission Factors Hub 2025 data.Open calculator Cost per kWh CalculatorCost per kWh calculator: divide your electric bill by the kWh used to find your all-in and energy-only price per kWh and compare it with the US average.Open calculator Electricity Cost CalculatorElectricity cost calculator: enter watts, hours per day and your rate to see what any device costs to run per hour, day, month and year.Open calculator Electricity Usage CalculatorElectricity usage calculator: pick an appliance or enter its watts to see kWh and cost per day, month and year. Typical wattages for 18 appliances.Open calculator Heat Pump vs Gas Cost CalculatorCompare a year of heating with a heat pump, natural gas, propane or heating oil. Uses EIA US average fuel prices; enter your own rates, HSPF2 and AFUE.Open calculator kWh CalculatorkWh calculator: convert watts and hours of use into kilowatt-hours per day and month, with Wh, MWh and the cost at your electricity price.Open calculator

EV charging calculators

What it costs to charge an electric car or a Tesla at home or at a fast charger.

EV Charging Cost CalculatorEV charging cost calculator: find the cost of one charge, cost per mile and monthly charging bill, and compare it with a gas car at your electricity price.Open calculator Tesla Charging CalculatorTesla charging calculator with Model 3, Y, S, X and Cybertruck presets: cost of a home charge, Supercharger cost, full charge cost and cost per mile.Open calculator

Backup power calculators

Size a UPS and estimate how long batteries will run your equipment.

Battery Runtime CalculatorBattery runtime calculator for UPS, inverter and solar batteries: enter watts, volts and amp-hours to see how many hours your battery backup will last.Open calculator UPS CalculatorUPS calculator: enter your load in watts to get the minimum VA and watt rating, convert VA to watts by power factor and find a standard UPS size to buy.Open calculator

Energy converters calculators

Convert watts, kilowatts, kWh, amps, amp-hours, mAh and BTU.

Amp Hours to kWhConvert amp hours to kWh with battery voltage: kWh = Ah × V ÷ 1,000. Includes usable energy for lithium and lead-acid and a 12, 24 and 48 V table.Open calculator Amp Hours to Watt HoursConvert amp hours to watt hours with Wh = Ah × V, or watt hours back to amp hours. Tables for 12, 12.8, 24 and 48 V batteries and power banks.Open calculator Amps to kWAmps to kW calculator for single-phase, three-phase and DC circuits. Convert amps to kilowatts with voltage and power factor, plus the 80% breaker load.Open calculator BTU to kWhConvert BTU to kWh, kWh to BTU and therms to kWh using 1 kWh = 3,412.14 BTU. Also turns BTU/h heating and cooling ratings into kW and tons.Open calculator kW to AmpskW to amps calculator for single-phase, three-phase and DC circuits. Convert kilowatts to amps with voltage and power factor, and get the breaker size.Open calculator kW to WattsKilowatt to watt converter: 1 kW = 1,000 W. Convert kW to W, watts to kW, megawatts, horsepower and BTU per hour, with a quick conversion table.Open calculator mAh to kWhConvert mAh to kWh and Wh using battery voltage, or kWh to mAh. Check whether a power bank is under the FAA 100 Wh carry-on limit for flights.Open calculator Watts to kWhConvert watts to kWh: multiply watts by hours and divide by 1,000. Free W to kWh calculator with a conversion table and the cost at the US average price.Open calculator

FAQ

Frequently asked questions

Are these renewable energy calculators free?

Yes. Every calculator is free, needs no sign-up and runs entirely in your browser, so the numbers you type are never sent to us.

How accurate are the results?

The formulas are standard engineering and physics equations with automated tests against worked examples. Results depend on your inputs, so use the rate from your bill and the specs of your own equipment for the best estimate.

Which calculator should I start with for solar panels?

Start with the solar panel calculator to size the system from your monthly kWh, then use the solar panel angle calculator to set the tilt. For a battery-based system, use the off-grid solar calculator.

What electricity price do the calculators use?

The default is 18.2¢ per kWh, the US residential average from the EIA for August 2026. Replace it with your own rate for an exact result.

Do the calculators work outside the US?

Yes. Enter your local electricity price and, for solar tools, your own latitude or sun hours. Results are shown in standard SI units such as kWh, kW and watts.