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Ohm’s Law Calculator | Solve Voltage, Current & Power

Solve for voltage, current, resistance or power in any circuit with Ohm's law and the power formula, entering any two values. The four rearrangements are shown with each step — the electrician's and electronics student's essential tool.

Last updated: June 2026 · Free · No sign-up required

Results

Enter values above and click Calculate to see your result instantly.

Quick reference

Ohm's law relationships:

KnowFind voltageFind power
I and RV = I x RP = I^2 x R
V and R—P = V^2 / R
V and I—P = V x I
P and IV = P / I—

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Interpretation guide

Quantities and units:

SymbolQuantityUnit
VVoltageVolts
ICurrentAmperes
RResistanceOhms
PPowerWatts

lightbulb Worked example

Let's say you are using the Ohms Law Calculator. Solves Ohm's law problems for voltage, current, resistance, and power. Enter any two values — for example voltage and resistance — and the tool computes the missing ones using V = IR and P = VI, with Enter the values that match your situation into the input fields and press calculate — using realistic numbers makes the result directly useful for you.

Result: The calculator instantly applies the formula V = I x R; P = V x I; combine to get P = I^2 R = V^2 / R and returns the result with appropriate precision.

What this means: Read the result in the context of what you are measuring. The step-by-step breakdown lets you confirm the math and understand which input most affects the outcome.

Formula & methodology

Formula: V = I x R; P = V x I; combine to get P = I^2 R = V^2 / R

The Ohms Law Calculator is built on a well-established calculation method. It uses the formula V = I x R; P = V x I; combine to get P = I^2 R = V^2 / R to turn your inputs into a reliable result. Solves Ohm's law problems for voltage, current, resistance, and power. Enter any two values — for example voltage and resistance — and the tool computes the missing ones using V = IR and P = VI, with the working The steps are shown on the page so you can follow the reasoning from input to output.

Ohm's law states that voltage equals current times resistance (V = IR). Combined with the power law (P = VI), the calculator solves for any of the four quantities — voltage, current, resistance, or power — from any two known values. These relationships are the foundation of circuit analysis, used to size resistors, check current draw, and verify a component stays within its power rating.

Authoritative source: timeanddate.com

Frequently asked questions

What is Ohm's law?
The Ohms Law Calculator is free, private, and accurate: it runs entirely in your browser (no uploads, no accounts), applies the standard calculation, and explains each step so you can verify the result. Solves Ohm's law problems for voltage, current, resistance, and power. Enter any two values — for example voltage and resistance — and the tool computes the missing ones using V = IR and P = VI, with the working displayed. A fast check for electronics There is no limit on usage, and it works on any device.
How do I calculate power from voltage and current?
Enter the required values into the input fields and press the calculate button. The tool applies the formula V = I x R; P = V x I; combine to get P = I^2 R = V^2 / R and returns the result with a short explanation of each step, so you can check the working yourself.
How do I find current from power and voltage?
Use the power-law rearrangement I = P ÷ V: a 60 W bulb on 120 V draws 0.5 A. Combined with Ohm's law V = IR, the calculator solves for any two known values among voltage, current, resistance, and power. Current is what heats wires and determines breaker sizing, so this is the value electricians check first.
What is resistance measured in?
Resistance is measured in ohms (symbol Ω), named after Georg Ohm. One ohm is the resistance that allows one ampere to flow when one volt is applied — 1 Ω = 1 V/A. Larger values use kilo-ohms (kΩ) and mega-ohms (MΩ), and small values use milli-ohms. The calculator accepts these unit prefixes and converts them automatically.
Can I find resistance from power and current?
Yes — rearrange the power and Ohm's law equations: R = P ÷ I². A 60 W device drawing 0.5 A has a resistance of 60 ÷ 0.25 = 240 Ω. The calculator solves for resistance from any valid pair — voltage and current, voltage and power, or power and current — using the four rearrangements of V = IR and P = VI.
What does the Ohms Law Calculator do?
Solves Ohm's law problems for voltage, current, resistance, and power. Enter any two values — for example voltage and resistance — and the tool computes the missing ones using V = IR and P = VI, with the working displayed. A fast check for electronics. The calculator takes your inputs, applies the standard calculation, and returns a clear result so you can make an informed decision without doing the math by hand.
What formula does the Ohms Law Calculator use?
The Ohms Law Calculator applies the standard formula: V = I x R; P = V x I; combine to get P = I^2 R = V^2 / R. The tool walks through each step of the calculation so you can verify the numbers yourself.
Is the Ohms Law Calculator free and private?
Yes — the Ohms Law Calculator. There is no sign-up, no paywall, no trial, and no limit on how many calculations you can run. CalcaTools covers its costs with non-intrusive display advertising, so the calculator itself never asks for payment or restricts any feature.
How accurate is the Ohms Law Calculator?
The Ohms Law Calculator applies the standard formula: V = I x R; P = V x I; combine to get P = I^2 R = V^2 / R. It is tested against published worked examples before launch and uses native double-precision arithmetic, so results are accurate to typical precision for the values you enter — with no intermediate rounding that could distort the answer.

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