Volt Calculator

A volt calculator solves electrical problems in three modes and converts between energy units in a fourth. Each mode accepts flexible input: decimals, fractions, mixed numbers, and scientific notation.

Ohm's Law (V, I, R) mode solves for voltage, current, resistance, and power from any two known values. V = I x R gives the missing electrical quantity, and P = V x I gives power from the result. A 12 V supply across a 6 ohm resistance, for example, draws 2 A and dissipates 24 W.

Power (V, I, W) mode works from voltage, current, and wattage instead: any two of the three yield the third along with resistance. A 120 V supply drawing 600 W, for example, carries 5 A at 24 ohms of resistance. Which mode applies depends on which two measurements a circuit or device specification actually provides.

Energy Converter (eV, J, Wh, kWh) mode converts, in either direction, between electron-volts, joules, watt-hours, and kilowatt-hours. Scientific notation covers the very large or very small values these units span, such as 1.602e-19 for the electron charge in joules.

A 9 V battery across a 47 ohm resistor draws I = V / R = 9 / 47 = 0.191 A, and dissipates P = V x I = 9 x 0.191 = 1.72 W.

Every field accepts several formats, useful since circuit specifications are not always given as plain decimals:

• Decimals: 12.5, 0.75, 3.3
• Fractions: 3/4, 1/2, 7/8
• Mixed numbers: 1 1/2, 5 3/4, 2-1/4
• Scientific notation: 1.5e3, 6.022e23, 1.602e-19

Settings holds the number of decimal places shown in results, from 2 to 10, and a step-by-step formula view that reveals the symbolic formula, the substituted values, and the computed result for each calculation. Inputs and settings persist between sessions.

Voltage, current, resistance, and power relationships form the foundation of circuit analysis and electrical system design. Converting between energy units bridges particle physics measurements with practical electrical engineering values.

• Circuit Design: the correct resistor value for an LED circuit follows from the supply voltage and the desired current draw; a 5 V supply targeting 0.02 A needs 250 ohms of resistance.
• Appliance Analysis: the current draw of a household appliance follows from its wattage rating and supply voltage; a 1500 W space heater on a 120 V circuit draws 12.5 A, a figure worth checking against the circuit breaker's rating.
• Solar Panel Sizing: power output follows from measured voltage and current under load; a panel producing 18 V at 5.5 A delivers 99 W.
• Battery Capacity: watt-hours convert to kilowatt-hours for comparing battery pack specifications across manufacturers; a 500 Wh battery equals 0.5 kWh, the unit utility bills use.
• Physics Education: Ohm's Law and power-equation homework problems check step by step, with the formula display showing V = I x R substituted with actual values.
• Particle Physics: electron-volt measurements convert to joules for cross-referencing experimental data against SI-based calculations; the 13.6 eV hydrogen ionization energy converts to approximately 2.179e-18 J.
• Electrical Safety: wire gauge adequacy follows from the current a known voltage and resistance combination draws; a 240 V circuit with 10 ohms of resistance draws 24 A, which needs at minimum 10 AWG wire.
• Motor Selection: matching a motor to a power supply means checking that available voltage and the motor's rated current keep power consumption within the driver circuit's acceptable limits.