Ohm's Law Calculator · Practical guide
Ohm's Law Wheel: All 12 Formulas Explained
Every voltage, current, resistance, and power formula from the wheel — with worked numbers for each.
At a glance
What the Wheel Shows
The Ohm's Law wheel collects the 12 ways to combine the four electrical quantities — voltage (V), current (I), resistance (R), and power (P). With any two known values, the wheel gives you the formulas for the other two. They all derive from two base relationships: V = I × R and P = V × I.
Interactive tool
Ohm's Law Calculator
Enter your own values, then compare the result with the examples below.
Ohm's Law Results
The Complete Formula Table
| Solve For | Formulas |
|---|---|
| Voltage (V) | V = I × R V = P / I V = √(P × R) |
| Current (I) | I = V / R I = P / V I = √(P / R) |
| Resistance (R) | R = V / I R = V² / P R = P / I² |
| Power (P) | P = V × I P = I² × R P = V² / R |
Worked Example From One Known Pair
Suppose you know a device runs at 12 V and draws 2 A. The wheel hands you the rest directly: R = V / I = 12 ÷ 2 = 6 Ω, and P = V × I = 12 × 2 = 24 W. Start from a different pair and the other formulas take over — knowing only that a resistor is 6 Ω and dissipates 24 W, you get V = √(P × R) = √144 = 12 V and I = √(P / R) = √4 = 2 A, the same circuit from the other direction.
Using the Wheel Without Memorizing It
You never need all 12 formulas in your head: remember V = I × R and P = V × I, and algebra supplies the rest. Or skip the algebra entirely — enter any two of the four values in the calculator above, and it solves the remaining two and shows exactly which wheel formulas it applied.
Frequently Asked Questions
What are the three basic Ohm's Law formulas?
V = I × R, I = V / R, and R = V / I. Every other formula on the wheel comes from combining these with the power equation P = V × I.
Why are there three formulas for each quantity?
Each version covers a different pair of known values. Voltage, for instance, can be found from current and resistance, from power and current, or from power and resistance — whichever two you happen to know.
What does P = I²R tell you in practice?
It explains why power losses in wiring grow with the square of current: doubling the current quadruples the heat dissipated in the same wire. That is the reason long-distance transmission uses high voltage and low current.
Does the wheel apply to AC circuits?
It applies exactly to DC and to purely resistive AC loads using RMS values. With capacitors or inductors, reactance and phase angle enter the picture and impedance replaces simple resistance.