The Electricity Calculator collection covers the core formulas every electronics enthusiast, student, and technician needs. Solve circuit fundamentals with Ohm's Law Calculator, size wiring runs with the Voltage Drop Calculator, find combined resistance with the Resistors in Series and Parallel Resistor calculators, and select the right current-limiting component with the LED Light Resistor Calculator.
Check the Popular list to jump straight to the most-used tools, or visit the Trending tab to discover what builders are working on. All calculators are free, need no sign-up, and run on any device.
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Wire Resistance CalculatorCalculate the electrical resistance of a wire from its resistivity, length, and cross-sectional area using R = ρL/A. Free online tool.
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18650 Battery Pack CalculatorCalculate the voltage, capacity (Ah), total cell count and energy (Wh) of an 18650 battery pack from any series-parallel (SxP) configuration.
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kVA to kW CalculatorConvert apparent power (kVA) to real power (kW) using the power factor. Free kVA to kW calculator with reactive power (kVAR) output.
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Appliance Run Time Battery CalculatorEstimate how long a battery will power an appliance from its Ah capacity, voltage, load watts and system efficiency. Free runtime calculator.
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EV Cost Per Mile CalculatorCalculate the energy cost per mile of your electric vehicle from its efficiency (miles/kWh) and your electricity rate. See cost per 100 miles and trip cost.
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Resistivity CalculatorCalculate the electrical resistance of a wire from its resistivity, length, and cross-sectional area using R = ρL/A. Free, instant, accurate.
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Home Solar Panel CalculatorEstimate how many solar panels and what system size (kW) you need based on your monthly electricity use, peak sun hours, panel wattage and efficiency.
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Voltage Drop Calculator (mm²)Calculate cable voltage drop in volts and percent for single-phase and three-phase copper or aluminium conductors sized in mm², by current and length.
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3 Phase Voltage Drop CalculatorCalculate three-phase voltage drop from load current, cable length, conductor resistivity, cross-section and power factor. Get volts dropped and percentage.
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18650 Battery Pack CalculatorCalculate the voltage, capacity (Ah), total cell count and energy (Wh) of an 18650 battery pack from any series-parallel (SxP) configuration.
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DC Voltage Drop CalculatorCalculate DC voltage drop across wire from current, length, and resistance. Get volts dropped, drop percentage, and voltage at the load instantly.
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Hydropower Output CalculatorCalculate hydroelectric power output from water flow rate, head, and efficiency using P = ρgQHη. Results in watts and kilowatts.
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Resistivity CalculatorCalculate the electrical resistance of a wire from its resistivity, length, and cross-sectional area using R = ρL/A. Free, instant, accurate.
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Capacitive Voltage Divider CalculatorCalculate the output voltage of a resistive voltage divider using Vout = Vin × R2 / (R1 + R2). Also gives divider ratio, current and power.
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Running Amps and Startup Load CalculatorSize a generator by adding running watts plus the largest startup surge. Enter your appliances to find the minimum wattage and a recommended size.
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VinFast Charge Time from Amps CalculatorEstimate VinFast EV charging time from charger power (kW), battery capacity, and start/target charge percent. Quick, simple hours and minutes estimate.
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Voltage Divider CalculatorCalculate the output voltage of a resistive voltage divider from Vin, R1 and R2. Also finds loop current and total power dissipated.
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Wire Resistance CalculatorCalculate the electrical resistance of a wire from its resistivity, length, and cross-sectional area using R = ρL/A. Free online tool.
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Wire Resistance CalculatorCalculate the electrical resistance of a wire from its resistivity, length, and cross-sectional area using R = ρL/A. Free online tool.
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18650 Battery Pack CalculatorCalculate the voltage, capacity (Ah), total cell count and energy (Wh) of an 18650 battery pack from any series-parallel (SxP) configuration.
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kVA to kW CalculatorConvert apparent power (kVA) to real power (kW) using the power factor. Free kVA to kW calculator with reactive power (kVAR) output.
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Appliance Run Time Battery CalculatorEstimate how long a battery will power an appliance from its Ah capacity, voltage, load watts and system efficiency. Free runtime calculator.
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EV Cost Per Mile CalculatorCalculate the energy cost per mile of your electric vehicle from its efficiency (miles/kWh) and your electricity rate. See cost per 100 miles and trip cost.
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Resistivity CalculatorCalculate the electrical resistance of a wire from its resistivity, length, and cross-sectional area using R = ρL/A. Free, instant, accurate.
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Impedance Calculator (Z from R and X)Calculate AC impedance Z from resistance R and reactance X using Z = √(R² + X²). Also returns the phase angle θ in degrees instantly.
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Electricity Usage From Meter Reading CalculatorCalculate kWh used between two electricity meter readings. Enter current and previous readings plus a meter multiplier to get usage and estimated cost.
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VinFast Charge Time from Amps CalculatorEstimate VinFast EV charging time from charger power (kW), battery capacity, and start/target charge percent. Quick, simple hours and minutes estimate.
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Three Phase Power CalculatorCalculate three phase real power (kW), apparent power (VA) and reactive power (VAR) from line voltage, line current and power factor using P = √3·VL·IL·cosφ.
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Capacitive Voltage Divider CalculatorCalculate the output voltage of a resistive voltage divider using Vout = Vin × R2 / (R1 + R2). Also gives divider ratio, current and power.
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Resistor CalculatorCalculate total resistance for resistors in series or parallel. Enter up to 4 resistor values in ohms and get the equivalent resistance instantly.
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Running Amps and Startup Load CalculatorSize a generator by adding running watts plus the largest startup surge. Enter your appliances to find the minimum wattage and a recommended size.
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Voltage Divider CalculatorCalculate the output voltage of a resistive voltage divider from Vin, R1 and R2. Also finds loop current and total power dissipated.
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Wire Gauge (AWG) CalculatorConvert American Wire Gauge (AWG) to conductor diameter and cross-sectional area, and estimate copper wire current capacity (ampacity) by density.
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Home Solar Panel CalculatorEstimate how many solar panels and what system size (kW) you need based on your monthly electricity use, peak sun hours, panel wattage and efficiency.
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Voltage Drop Calculator (mm²)Calculate cable voltage drop in volts and percent for single-phase and three-phase copper or aluminium conductors sized in mm², by current and length.
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3 Phase Voltage Drop CalculatorCalculate three-phase voltage drop from load current, cable length, conductor resistivity, cross-section and power factor. Get volts dropped and percentage.
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DC Voltage Drop CalculatorCalculate DC voltage drop across wire from current, length, and resistance. Get volts dropped, drop percentage, and voltage at the load instantly.
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Hydropower Output CalculatorCalculate hydroelectric power output from water flow rate, head, and efficiency using P = ρgQHη. Results in watts and kilowatts.
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Watt's Law CalculatorFree Watt's Law calculator. Solve for power (P), voltage (V), or current (I) using P = V × I. Enter any two values to find the third instantly.
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Electricity Units to kWh CalculatorConvert electricity units to kilowatt-hours (1 unit = 1 kWh) and estimate your bill cost from units consumed and your per-unit tariff.
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Monthly Electricity Cost from Watts CalculatorCalculate the monthly electricity cost of any device from its wattage, daily usage hours and your per-kWh rate. Get daily, monthly and yearly estimates.
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Motor Torque from kW and RPM CalculatorCalculate electric motor torque in newton-metres from power (kW) and speed (RPM) using T = 9549 x kW / RPM. Includes lb-ft conversion.
Frequently asked questions
What electrical calculations can I do here?
You can apply Ohm's Law to find voltage, current, or resistance; calculate total resistance for series and parallel networks; determine safe voltage drop across a wire run; find the right resistor for an LED circuit; and decode resistor color bands instantly with the Resistor Color Code Calculator.
Are these calculators free?
Yes — completely free, no account needed, and nothing to install. Open any tool on a phone, tablet, or computer and get your answer right away.
How accurate are the results?
The tools use well-established electrical engineering formulas including Ohm's Law, Kirchhoff's voltage law, and standard voltage-drop equations. Results are suitable for educational use and prototype planning. For installations governed by safety codes, always verify your calculations against the applicable electrical standard such as NEC or IEC 60364 and have a qualified electrician or engineer review the design.
Are my circuit values saved?
No. Every calculation runs locally in your browser. The resistances, voltages, and currents you enter are never stored on our servers or transmitted anywhere.
Which electrical calculators are most popular?
The Popular list is sorted by real user traffic, with the most-used tools at the top. You can also browse Trending for fast-moving picks, Recently Added for the newest calculators, or Last Updated for recently revised entries.
