What is the Volts, Amps, Watts, Ohms Calculator?
This calculator solves the four fundamental electrical quantities — voltage (V), current (I), resistance (R), and power (P) — using Ohm's law and the power triangle. Enter any two known values and the tool computes the remaining two instantly. It is a universal physics/electronics tool that works for any DC circuit (and resistive AC circuits using RMS values).
How to use it
Type in exactly two of the four fields and leave the other two blank. For example, enter a power rating and a resistance to find the voltage and current, or enter voltage and current to find resistance and power. Click calculate and read the full set of results in the table.
The formulas explained
Ohm's law links voltage, current and resistance: $$\text{V} = \text{I} \times \text{R}$$ Electrical power is the rate of energy transfer: $$\text{P} = \text{V} \times \text{I}$$ Substituting Ohm's law gives the two convenient forms \(\text{P} = \text{I}^2 \times \text{R}\) and \(\text{P} = \text{V}^2 / \text{R}\). From any pair of known quantities, algebra recovers the rest — for instance, with P and R known, \(\text{V} = \sqrt{\text{P} \cdot \text{R}}\) and \(\text{I} = \sqrt{\text{P}/\text{R}}\).
Worked example
Suppose a heating element dissipates 100 W into a 25 Ω resistance. Then $$\text{V} = \sqrt{100 \times 25} = \sqrt{2500} = 50\ \text{V}$$ and $$\text{I} = \sqrt{100 / 25} = \sqrt{4} = 2\ \text{A}$$ Checking: \(\text{P} = \text{V} \times \text{I} = 50 \times 2 = 100\ \text{W}\) ✓.
FAQ
Which two values should I enter? Any two — the math is symmetric. Just make sure they are physically consistent.
Does this work for AC? Yes for resistive (purely real) loads if you use RMS voltage and current. Reactive loads with capacitance or inductance require power factor and are not covered.
Why do I get zero? A divide-by-zero is guarded; if a needed quantity is zero (e.g. resistance 0 with current unknown) the result may be 0 — recheck your inputs.
