Ohm’s Law Calculator.

Formula and practical context.

Formula, variables, and method

V = I × R; I = V ÷ R; R = V ÷ I; P = V × I. Field labels below follow the selected operation; values use volts, amperes, ohms, and watts without automatic metric prefixes. Ohm’s law relates voltage, current, and resistance, while electrical power provides a useful fourth derived quantity. Start by identifying what each entered number represents and whether it is a measured value, a specification, or an assumption. Convert units before combining quantities, preserve full precision through intermediate steps, and round only the displayed result. Choose the unknown, enter the two required known values, and verify the rearranged relation: V = I×R, I = V÷R, R = V÷I, or P = V×I. This sequence makes the output reproducible and helps expose a misplaced unit or decimal point before it affects a decision.

Worked example and independent check

A 12 volt source across 6 ohms produces 2 amperes; the corresponding power is 24 watts. To check the example independently, write the formula first, substitute the values with their units, and complete one operation at a time. Compare the order of magnitude with a familiar reference rather than accepting a formatted result automatically. Choose the unknown, enter the two required known values, and verify the rearranged relation: V = I×R, I = V÷R, R = V÷I, or P = V×I. If a second method or inverse calculation is available, use it to recover an original input. Small differences from hand calculation should come only from displayed rounding, not from a different definition.

Units and result interpretation

Use volts, amperes, ohms, and watts. Prefixes such as milliamperes or kilo-ohms must be converted before entering a value. Ohm’s law relates voltage, current, and resistance, while electrical power provides a useful fourth derived quantity. A unit is part of the quantity, not a label added after the arithmetic. Keep decimal and binary prefixes, temperature scales, elapsed-time units, and electrical prefixes explicit. When comparing two scenarios, change one assumption at a time and retain the same unit convention. The result describes only the relationship named by this calculator; it does not automatically establish capacity, safety, compatibility, quality, or compliance.

Validation and boundary cases

A divisor cannot be zero, all entered magnitudes must be nonnegative, and a calculated result must remain finite. Blank values, malformed text, non-finite numbers, impossible ranges, zero divisors, and unsupported combinations receive an explicit message rather than a silent fallback. Boundary values are checked before the formula runs. If an input comes from a specification sheet, weather report, network plan, or measurement instrument, confirm its definition and precision. A syntactically valid value can still be unsuitable for the real situation, so inspect the assumptions alongside the result.

Assumptions, privacy, and practical limits

Real components can be nonlinear, temperature-dependent, reactive, pulsed, or outside their ratings; this calculator models a resistive DC relationship. All entered values are processed in the browser and are not sent to a calculation service. Use the result as a transparent estimate or transformation, keep the source values with any saved result, and consult the linked authoritative material for definitions and applicability. For safety-critical, health-adjacent, security, network, chemical, or electrical work, verify the result with current standards, official warnings, qualified professionals, and appropriate test equipment.

Check assumptions and sources.

Real components can be nonlinear, temperature-dependent, reactive, pulsed, or outside their ratings; this calculator models a resistive DC relationship.

NIST SI unit of electric current