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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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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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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kWh from Amps, Volts and Hours CalculatorCalculate electricity usage in kWh from amps, volts and hours. Enter current, voltage and run time to get energy used, power in watts and cost.
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Electric Field of a Point Charge CalculatorCalculate the electric field E of a point charge using E = kQ/r². Enter charge Q in coulombs and distance r in meters to get the field in N/C.
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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.
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Battery Discharge Time CalculatorEstimate how long a battery will last from its amp-hour capacity, load current, and usable depth of discharge. Free runtime calculator: t = (Ah × DoD) / A.
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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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Electricity Bill CalculatorEstimate your electricity bill from units consumed (kWh), the per-unit rate, and any fixed charge. Free, fast, and works with any currency.
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Power from Torque and RPM CalculatorCalculate mechanical power in kW, watts and horsepower from torque (N·m) and rotational speed (RPM) using P = T × RPM / 9549.
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Milliamps to Amps CalculatorConvert milliamps (mA) to amps (A) instantly. Enter a current in mA and get the value in amperes using A = mA / 1000.
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EV kWh per 100 km CalculatorCalculate your electric vehicle energy consumption in kWh per 100 km from the energy used and distance driven. Get km/kWh and Wh/km too.
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EV vs Gas Cost per Mile CalculatorCompare the cost per mile of driving an electric vehicle versus a gas car. Enter kWh/mile, electricity price, gas price, and MPG to see your savings.
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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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kWh to BTU CalculatorConvert kilowatt-hours (kWh) to British Thermal Units (BTU) instantly. Enter kWh and get BTU using the factor 1 kWh = 3412.142 BTU.
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Amps to Milliamps CalculatorConvert amps (A) to milliamps (mA) instantly. Enter a current value in amperes and get the equivalent in milliamps using mA = A × 1000.
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Battery Amp-Hours Needed CalculatorCalculate the battery amp-hours (Ah) needed from watts, runtime hours and voltage. Includes depth-of-discharge adjustment for any 12V, 24V or 48V battery.
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Battery State of Charge CalculatorEstimate battery State of Charge (SOC %) from a measured voltage reading using linear interpolation between empty (Vmin) and full (Vmax) voltages.
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Electric Field Between Plates CalculatorCalculate the uniform electric field between two parallel plates using E = V/d from the voltage and plate separation. Fast, free physics tool.
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.
