Electrical, Energy & Weather Calculators
From sizing a wire run to decoding a resistor's color bands, these calculators apply the standard engineering formulas so you get consistent results. The weather tools use the same formulas national weather services publish for wind chill, heat index and dew point.
Electrical results are estimates for planning. Follow your local electrical code and consult a licensed electrician for installations.
Electrical & Energy tools
Voltage Drop Calculator
Free voltage drop calculator for copper or aluminum wire. Enter AWG gauge, amps, one-way length, and system voltage to get drop percent and end voltage.
Resistor Calculator
Free resistor color code calculator for 4, 5, and 6-band resistors. Pick the band colors to get resistance, tolerance, and the min and max values.
Ohms Law Calculator
Free Ohm's law calculator. Enter any two known values to solve for voltage, current, resistance, or power, with V = I x R and P = V x I formulas shown.
Electricity Cost Calculator
Free electricity cost calculator. Add appliances by wattage and hours of use per day to estimate daily, monthly, and yearly kWh and cost at your rate.
Wind Chill Calculator
Free wind chill calculator using the NWS formula. Enter temperature in °F or °C and wind speed in mph or km/h to get feels-like temp and frostbite risk.
Heat Index Calculator
Free heat index calculator to find feels-like temperature based on heat and humidity. Get health risk warnings.
Dew Point Calculator
Free dew point calculator. Enter air temperature and relative humidity to get the dew point, spread, absolute humidity, and a comfort level rating.
Battery Runtime Calculator
Battery runtime calculator: estimate how long a lead-acid, AGM or LiFePO4 battery will run a load, with depth of discharge and inverter losses.
Dehumidifier Size Calculator
Dehumidifier size calculator: find the pints per day you need from room area and dampness using the AHAM sizing chart, with notes on 2019 ratings.
Generator Size Calculator
Generator size calculator: tick your appliances to total running watts, peak starting surge and a recommended generator size with 20% headroom.
Solar Panel Calculator
Solar panel calculator: estimate the system size in kW, number of panels and yearly production from your kWh usage and local peak sun hours.
Water Heater Size Calculator
Water heater size calculator: find the first-hour rating for a tank heater or the GPM and temperature rise for a tankless unit.
Wire Gauge Calculator
Free wire gauge calculator: find the smallest AWG copper or aluminum wire that meets NEC ampacity and 3% voltage drop for your amps, volts and run length.