Power Triangle Calculator (P, V, I, R)
Calculate any two unknowns from the power triangle: P=VI, V=IR, P=I²R, P=V²/R. Select which two values you know and the calculator finds the rest.
How to use this tool
- Enter known values, voltage v, current i, resistance r and power p in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your power p and the full breakdown beneath it.
The power triangle links voltage V, current I, resistance R and power P through: P = VI = I²R = V²/R and V = IR. Select which two values you know and all four are solved instantly.
Formula
P = V × I | V = I × R | P = I2 × R | P = V2 ÷ R
Given any two of P (W), V (V), I (A), R (Ω), the remaining two are solved using Ohm's law and the power formula.
How it works
The power triangle relates power (P), voltage (V), current (I), and resistance (R) through two fundamental equations: Ohm's law V = IR and the power relation P = VI. Selecting any two known quantities allows the other two to be derived algebraically.
The calculator supports all six two-known-quantity modes and rounds every output to 4 decimal places. It assumes a purely resistive, DC (or RMS AC) circuit; reactive components such as capacitors and inductors are not modelled.
Worked example
Worked example (V and I known)
- Given: Voltage V = 12 V, Current I = 2 A (mode: VI).
- Power: P = V × I = 12 × 2 = 24 W.
- Resistance: R = V ÷ I = 12 ÷ 2 = 6 Ω.
Power P = 24 W, Resistance R = 6 Ω, Voltage V = 12 V, Current I = 2 A.
Key terms
- Ohm's law
- The relationship V = IR stating that voltage across a resistor equals current through it multiplied by its resistance.
- Power (P)
- The rate at which electrical energy is transferred or dissipated, measured in watts (W). P = VI for DC circuits.
- Resistance (R)
- Opposition to the flow of electric current in a conductor, measured in ohms (Ω).
- Current (I)
- The rate of flow of electric charge through a conductor, measured in amperes (A).
- Voltage (V)
- The electric potential difference between two points in a circuit, measured in volts (V).
Frequently asked questions
- How is this different from the Ohm's Law calculator?
- The Ohm's Law calculator solves V=IR for three variables. This tool adds the power equations (P=VI, P=I²R, P=V²/R) and lets you start from any two of the four quantities P, V, I, R.
- What are real-world examples?
- A 60 W light bulb on 120 V draws I = P/V = 0.5 A, with R = V/I = 240 Ω.