What is the difference between this and a basic Ohm's Law calculator?

This tool also shows power in both watts and milliwatts and lets you solve for V, I or R directly. The 'power wheel' name refers to the circular diagram in textbooks showing all 12 formula variants.

Why do I enter 0 for the unknown?

Entering 0 signals that the value is unknown. The calculator then derives it from the other two entered values.

Electronics Power Wheel (V, I, R, P)

Solve for any one of voltage (V), current (I), resistance (R) or power (P) using Ohm's Law and power formulas P=VI=I²R=V²/R. Enter any two to find the rest.

By AbraCalc Editorial Team · Reviewed by AbraCalc Methodology Review · Last reviewed: 2026-06-25

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How to use this tool

Enter voltage (v), current (i) and resistance (r) in the fields above.
Results update instantly as you type — or click Calculate.
Read your power and the full breakdown beneath it.

The electronics power wheel (also called the Ohm's Law wheel) combines Ohm's Law (V = IR) with the power equations (P = VI = I²R = V²/R). Enter any two known quantities and all four are calculated instantly.

Formula

Ohm's Law: V = I × R (solve for the zero-valued unknown)

Power: P = V × I = I² × R = V² / R

Enter any two of V, I, R (set the unknown to 0) to compute all four quantities.

How it works

The electronics power wheel is a reference that combines Ohm's Law with the three power equations into one solver. The calculator detects which of V, I, or R is set to zero, derives the missing value using the two known quantities, then computes power by all three equivalent formulas for verification.

All three power expressions (P = VI, P = I²R, P = V²/R) should give the same result; tiny floating-point differences are rounded away. The tool assumes a purely resistive (DC) load; it does not account for reactive (AC) components or non-linear devices.

Worked example

Worked example — V = 12 V, I = 0.5 A, R unknown

Inputs: V = 12 V, I = 0.5 A, R = 0 (unknown).
Derive R = V / I = 12 / 0.5 = 24 Ω.
Power P = V × I = 12 × 0.5 = 6 W.
Verify: P = I²R = 0.25 × 24 = 6 W; P = V²/R = 144/24 = 6 W.

Power: 6.0 W (6000.0 mW) | Resistance: 24.0 Ω

Key terms

Ohm's Law: The fundamental relationship V = IR stating that voltage across a resistor equals current through it multiplied by its resistance.
Power (P): The rate of energy transfer in a circuit, measured in watts. In resistive circuits P = VI = I²R = V²/R.
Power Wheel: A circular diagram (Pie chart layout) grouping all 12 expressions for V, I, R, and P so engineers can quickly find any quantity from any two known values.
Resistive Load: A load that converts electrical energy entirely to heat with no reactive (inductive or capacitive) component; Ohm's law applies directly.
Milliwatt (mW): One thousandth of a watt (10⁻³ W). Commonly used for low-power electronics such as LEDs, sensors, and microcontroller peripherals.

Frequently asked questions

What is the difference between this and a basic Ohm's Law calculator?: This tool also shows power in both watts and milliwatts and lets you solve for V, I or R directly. The 'power wheel' name refers to the circular diagram in textbooks showing all 12 formula variants.
Why do I enter 0 for the unknown?: Entering 0 signals that the value is unknown. The calculator then derives it from the other two entered values.