Use the calculation modes
- Choose a mode from Calculation mode.
- Enter the requested values and select the available units, material, or circuit type.
- Click Calculate.
- Review Result, Formula & steps, Assumptions, and warnings.
- Choose Copy result or Download result (.txt) to keep the output.
Calculate watts, volts, amps, and resistance
In Watts / volts / amps / resistance (Ohm's law), enter exactly two of Voltage (V), Current (A), Resistance (Ω), and Power (W). The other two values are calculated.
Voltage (V): 120
Current (A): 2
Power (W): 240
Resistance (Ω): 60Resistor combinations need at least two positive values in Resistor values (ohms, comma-separated). Select Series or Parallel in Combination type. Series adds the values; Parallel uses the reciprocal-sum formula.
Check voltage drop and estimate wire size
Voltage drop uses Current (A), One-way length, Length unit, Conductor material, Wire gauge, Conductor temperature (°C), Circuit type, and Supply voltage (V). The one-way length is converted to meters. DC / single-phase uses a round-trip factor, while Three-phase uses a square-root-of-three factor.
Wire-size estimate uses Current (A), One-way length, Length unit, Conductor material, Conductor temperature (°C), Circuit type, Supply voltage (V), and Max allowed voltage drop (%). It checks standard AWG sizes 18 through 4/0 and reports the smallest size that meets the target. The calculation covers voltage drop; ampacity, breaker sizing, grounding, local code, kcmil sizes, and parallel runs are outside it.
Estimate battery runtime and energy use
Battery runtime converts Battery capacity and Load (power draw) through Capacity unit and Load unit. Voltage (V) is required when capacity uses mAh or Ah, or load uses mA or A. Efficiency (%) is applied to the capacity before runtime is divided by load power. The calculation assumes constant load power and discharge voltage, and leaves out temperature, aging, non-linear discharge, and Peukert's law.
Battery-bank sizing uses Daily energy need (Wh/day), Autonomy (days), System voltage (V), Depth of discharge (%), Individual battery capacity (Ah), and Individual battery voltage (V). It rounds up to whole batteries and warns when the series voltage does not exactly match the requested system voltage. Energy consumption uses Power, Hours used per day, Number of days, and optional Electricity rate per kWh. Hours used per day must be 24 or less.
Choose a related calculator
Use Ohm's Law Calculator for voltage, current, resistance, or power from two values. Choose Voltage Drop Calculator for voltage drop across one wire run. Use Battery Runtime Calculator when capacity, load, voltage, and efficiency are the only inputs you need. Browse Science Calculators for the other science calculation categories.
Frequently asked questions
What can an electrical calculator calculate?
This Electrical Calculator has modes for Ohm's law and power, resistor combinations, voltage drop, wire-size estimates, battery runtime, battery-bank sizing, and energy consumption. Select one in Calculation mode.
How do I calculate voltage drop and wire size?
Enter the current, one-way length, conductor details, circuit type, and supply voltage. Wire-size mode also needs Max allowed voltage drop (%), then checks AWG sizes 18 through 4/0 for the smallest size that meets the target.
Does the calculator check ampacity or electrical code?
It estimates voltage drop. Ampacity, breaker or fuse sizing, grounding, and compliance with NEC, CEC, IEC, or another local code require separate checking.
How is battery runtime calculated?
Runtime is usable watt-hours divided by load watts, with the entered Efficiency (%) applied to capacity. The calculation assumes constant load power and discharge voltage. The calculator processes inputs locally, and its script makes no request containing those values.