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Ohmic Resistor: Voltage, Current and Power

Solve voltage, current, resistance and dissipated power for one ideal ohmic resistor, with editable inverse controls and independent electrical units.

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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

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Formula and method

A 12 V drop across 6 Ω produces 2 A and dissipates 24 W.

V = IR; P = VI = I²R = V²/R.

Worked example

Enter these known values and leave the other values blank.

Voltage drop magnitude
12 V
Resistance
6 Ω
Current magnitude
2 A
Dissipated power
24 W

Assumptions and limitations

  • The component is an ideal ohmic resistor at a fixed operating temperature. Nonlinear devices, reactive impedance and thermal drift are not modeled.
  • Voltage and current are magnitudes. Resistance and voltage must be positive in the retained inverse model; current and power accept zero as limiting inputs, which may leave a singular inverse incomplete.
  • For alternating current this resistive relation applies to consistent RMS quantities. It does not calculate complex impedance, power factor or peak-to-RMS conversion.
  • Edit any two independent quantities to infer the others. Locks retain known values; incompatible locked values produce a consistency warning.
  • Controls accept decimal/scientific-notation numbers and bounded exact finite-decimal arithmetic. Expressions that lose input digits or exceed the proof budget are rejected. Nonzero entered values below 10⁻¹⁰⁰⁰⁰ in equation base units are outside the supported working range. Arithmetic results use 64 significant digits; tiny representable values use scientific notation, and an overflowing or zero-losing unit conversion is withheld with an error.
  • The BTU/h power selector retains the captured rounded factor 50000/170607 watts per BTU/h (about 0.29307121 W), rather than the International Table BTU/h factor 0.29307107017 W. This is approximately 0.0000479% higher; use watts or SI prefixes for precision work.

Common questions

Which two quantities are enough?

Voltage and resistance determine current and power. Any other independent pair can also determine the operating point in the positive domain.

Why is power positive?

The resistor converts electrical energy to heat. With positive resistance, I²R is nonnegative.

Does this include a resistor power rating?

No. The computed dissipation must be compared with a separate rating, ambient temperature and manufacturer derating requirements.

References

The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.

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