Ohm's Law Calculator
Calculate ohm's law step by step: V = I × R.
In short
Formula: V = I × R. Rearranged: I = V ÷ R and R = V ÷ I. Power is also shown as P = V × I.
Voltage
12 V
- Power (V × I)
- 24 W
What this calculator does
Calculate ohm's law step by step: V = I × R. Worked example, questions and limitations included.
Use it to turn Solve for, Voltage, Current, Resistance into a checked result you can compare, copy, or rerun with different assumptions.
The page shows the formula, a numeric worked example, and the assumptions that affect this electrical calculation.
Inputs and what they mean
- Solve for
- — choice value.
- Voltage
- — number value.
- Current
- — number value.
- Resistance
- — number value.
How to use it
- Enter each value in the unit shown next to the box (use the unit converter first if your numbers are in other units).
- Check the breakdown to see every intermediate step.
- Read the limitations before relying on the result.
Formula
Ohm's law applies to ohmic (linear) conductors at a steady temperature.
Dividing by zero is blocked: resistance must be above zero to solve for current, and current must be non-zero to solve for resistance.
Units are volts, amperes and ohms; enter mA as 0.001 A and kΩ as 1000 Ω.
V = I × R. Rearranged: I = V ÷ R and R = V ÷ I. Power is also shown as P = V × I.
Inputs used: Solve for, Voltage, Current, Resistance.
Worked example
12 V across 6 Ω
- I = V ÷ R = 12 ÷ 6 = 2 A.
- P = V × I = 12 × 2 = 24 W.
Reading the result
The headline figure is the main answer. Any breakdown underneath shows the parts that make it up, so you can check the working and see what changes when you adjust an input.
Limitations and assumptions
- Assumes a constant resistance; real resistance rises or falls with temperature.
- Ignores wire, contact and internal source resistance.
- For AC with reactive loads, impedance and phase angle are not modelled.
- Results are estimates for planning and learning. Real designs, installations and bids must be checked by a qualified, licensed professional against the codes that apply where you work.
- The result depends on the values you enter for this ohm's law calculator; it does not supply missing rates, rules, prices, dates, or assumptions for you.
Common questions
Does Ohm's law work for LEDs and diodes?
Not directly. Diodes are non-linear, so their resistance changes with current. Use the LED resistor calculator, which subtracts the LED's forward voltage first.
Can I use it for AC circuits?
For purely resistive AC loads, yes, using RMS voltage and current. With motors, coils or capacitors you need impedance instead of resistance, and power factor matters.
Why does the power figure matter?
Every resistor has a power rating. If V × I exceeds that rating the part overheats, so pick a resistor rated comfortably above the calculated power.
How do I use the Ohm's Law Calculator?
Enter the required values for Solve for, Voltage, Current, Resistance. The calculator applies the formula on this page and shows the main result with any supporting breakdown so you can check the arithmetic.
What formula does the Ohm's Law Calculator use?
V = I × R. Rearranged: I = V ÷ R and R = V ÷ I. Power is also shown as P = V × I. The visible formula section above lists the calculation path and the edge cases the page handles, so the result can be checked without relying on the form alone.
Can the Ohm's Law Calculator be used for exact decisions?
Use it as a calculation aid, not as a substitute for checking the underlying rule, contract, policy, or professional advice that applies to your situation. When a result depends on local rules, personal details, prices, or dates, enter those values yourself and confirm them before acting.
Related tools
Calculate electrical power step by step: P = V × I = I² × R = V² ÷ R (DC or resistive AC using RMS values).
Calculate voltage divider step by step: Vout = Vin × R2 ÷ (R1 + R2).
Calculate resistance step by step: R = V ÷ I, or for a conductor R = ρ × L ÷ A (A in m²).
Calculate series resistance step by step: R_total = R1 + R2 + … + Rn.