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Electrical calculator

Ohm's Law Calculator

Enter any two of voltage, current, resistance, and power to solve the remaining values. Runs locally in your browser. Free online tool — no sign-up.

Instant result
Result
—

Enter values to calculate.

Inputs—
Mode—
Formula—
Trust summary CVP VERIFIED · CVP protocol 1.0.0-proposed · Engineering assurance
Input interpretation
Enter values to calculate.
Result
—
Assurance
Engineering
Declared partition coverage
PASS · 4/4 declared partitions (pair-vi, pair-vr, with-power, invalid-domain) · Matrix
Known limitations
  • Resistive DC identities; SI only
  • Core CVP does not include live graph, viewport, or pointer interaction.
Model
Any two of V, I, R, P from the other two using Ohm's law and resistive power.
Scope
Ohmic (constant) resistance
Verification
Engine tested · Source checked · v1.5.1 · CVP VERIFIED · CVP protocol 1.0.0-proposed · Engineering assurance· View Manifest · CVP overview · Specification
Versions
Calculation 1.5.1 · CVP protocol 1.0.0-proposed
CVP identity
6/6 property · digest 7d608c5494dc
Legacy regression
18/18 tests · Production surface contract 3/3
Trust layers
Verification VERIFIED · Production CURRENT · overall VERIFIED
Reference
O1 model · O2 expected_values · O2 numerical_behavior
Interfaces
PASS · UI (SSR) / REST / MCP — ui-ssr is query-result HTML, not a live browser session.
Supplemental domain review
Internal · Pass · electrical-engineer
Named expert review
Not performed
CVP suite
4/4 golden · 4/4 CVP boundary · 4/4 invalid · 6/6 property · 1/1 cross-interface · 3/3 CVP contract · Manifest
Sources
Sources
Evidence
8 legacy golden · 4 legacy boundary · legacy regression suite · 4/4 oracle-backed golden · 4/4 invalid · Artifact integrity PASS · CalculatorX electrical review
This calculator CURRENT · Public schema 1.5.1 matches · Semantic contract ✓ · Production attested · Public/cache ✓ · Origin ✓
Semantic contract
PASS
Full verification

Manifest identity, reference classes, interfaces, suite, and production records.

Formulas

Core equations used by this calculator.

VoltageV = I × R
CurrentI = V ÷ R
ResistanceR = V ÷ I
PowerP = V × I = I²R = V² ÷ R
iValid for ohmic (resistive) materials at fixed temperature. Semiconductors and circuits with significant capacitance or inductance do not follow a simple constant R. For AC with impedance, use Z instead of R and VA for apparent power — this tool uses resistive P = V × I.

How to use

1

Enter any two values

Fill two of voltage (V), current (A), resistance (Ω), and power (W). Leave the other two blank.

2

Read the full set

The result shows all four quantities. The first two filled fields (top to bottom) are treated as the known pair.

3

Clear to start over

Use Clear when switching to a different known pair.

Example calculations

Common configurations with formula and result.

ϟ

Find R and P from V and I

24 V · 2 A

R = 24÷2 · P = 24×2
12 Ω · 48 W
ϟ

Find I and P from V and R

120 V · 60 Ω

I = 120÷60 · P = V×I
2 A · 240 W
ϟ

Find V and P from I and R

0.5 A · 220 Ω

V = 0.5×220
110 V · 55 W
ϟ

Find V and R from P and I

108 W · 6 A

V = 108÷6 · R = V÷I
18 V · 3 Ω
ϟ

Find I and V from P and R

48 W · 12 Ω

I = √(48÷12) · V = I×R
2 A · 24 V

Formula pairs (solve the other two)

Common values at a glance.

KnownFindFormulas
V, IR, PR = V÷I · P = V×I
V, RI, PI = V÷R · P = V×I
I, RV, PV = I×R · P = V×I
P, VI, RI = P÷V · R = V÷I
P, IV, RV = P÷I · R = V÷I
P, RI, VI = √(P÷R) · V = I×R
i Use volts, amps, ohms, and watts together. Convert mA→A (÷1000), kΩ→Ω (×1000), kV→V (×1000) before entering.

Ohm's Law calculator specification

Version 1.5.1 · Engine tested · Supplemental domain review · Internal · 2026-08-08

Calculation status

Review policy · Evidence · Reviewed by CalculatorX electrical review (electrical-engineer)

Definition
Ohm's law relates voltage, current, and resistance in a resistive circuit: V = I × R. Combined with Joule's law, power is P = V × I (also P = I²R and P = V²/R). Enter any two of V, I, R, and P — this calculator finds the other two for DC or resistive AC (RMS).
What it calculates
Any two of V, I, R, P from the other two using Ohm's law and resistive power.
Inputs
  • Any two of: voltage (V), current (A), resistance (Ω), power (W)
Outputs
  • The remaining two quantities
Formula
V=I·R; P=V·I; P=I²R; P=V²/R
Assumptions
  • Ohmic (constant) resistance
  • Resistive power P = V × I
Units
  • V, A, Ω, W
Boundary conditions
  • Fewer than two of V,I,R,P → NEEDS_TWO_INPUTS
  • Non-finite → INVALID_NUMBER
  • Zero divisor yields 0 for the dependent quantity — soft boundary
  • Resistive model only; not for reactive impedance networks
Example
24 V and 2 A → 12 Ω and 48 W
Validation cases

13 published on this page · 18/18 tests · Production surface contract 3/3 · View evidence

  • 24 V, 2 A → 12 Ω, 48 W
  • 120 V, 60 Ω → 2 A, 240 W
  • 108 W, 6 A → 18 V, 3 Ω
  • 48 W, 12 Ω → 2 A, 24 V
  • 48 V, 2 A (2× V) → 24 Ω, 96 W (linear in V for V+I)
  • 24 V, 4 A (2× I) → 6 Ω, 96 W
  • 12 V, 0 Ω → 0 A, 0 W (soft: zero divisor → 0)
  • 0 V, 10 A → 0 Ω, 0 W (soft: zero V → 0)
  • 0 W, 12 Ω → 0 A, 0 V
  • Only 24 V (one input) → error NEEDS_TWO_INPUTS
  • Empty inputs → error NEEDS_TWO_INPUTS
  • V=n/a, I=2 → error INVALID_NUMBER
  • 0 W, 0 A → 0 V, 0 Ω
Sources
Last reviewed
2026-08-08
Reviewed by
CalculatorX electrical review (electrical-engineer)
Calculation version
1.5.1

Background

Interpretation and common distinctions.

Enter any two of voltage (V), current (I), resistance (R), and power (P) to solve for the other two. Uses Ohm's law and resistive power:

V = I × R P = V × I

Default example: 24 V and 2 A → 12 Ω and 48 W.

Supported and not supported

Supported

  • Any two of V, I, R, P → closed {V, I, R, P}
  • Resistive DC / RMS AC
  • API capability electrical.ohms_law · pin calculation_version: 1.5.1

Not supported

  • Reactive impedance / complex Z
  • Semiconductor nonlinear V–I
  • Temperature-dependent R models

Stable errors: NEEDS_TWO_INPUTS, INVALID_NUMBER.

Electrical power

Power is the rate of energy transfer, in watts. In a resistive circuit:

P = V × I P = I² R P = (V²)/R

Example: 18 V and 6 A → P = 18 × 6 = 108 W.

Limits of Ohm's law

  • Applies to ohmic conductors (typical metal resistors) where R does not depend on V or I.
  • Temperature changes can change R.
  • Semiconductors, diodes, and many nonlinear devices do not follow V = IR with constant R.
  • With capacitors or inductors, use impedance Z and treat apparent power in VA, not this simple resistive model.

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Frequently asked questions

Key distinctions behind the calculation.

What is Ohm's law?

Ohm's law states that current through a conductor is proportional to the voltage across it when resistance is constant: V = I × R, or R = V ÷ I.

How do I use this calculator?

Enter any two of V, I, R, and P. The tool solves for the other two using V = I × R and P = V × I (or I = √(P÷R) when power and resistance are known).

What is the equation for power?

In a resistive circuit, P = V × I. Equivalently P = I² × R and P = V² ÷ R.

Does Ohm's law apply to semiconductors?

Not in the simple linear form. Semiconductors have nonlinear V–I curves. Use Ohm's law for resistors and other ohmic conductors under the conditions where R is constant.

Does it work for AC?

For purely resistive AC loads, use RMS voltage and current the same way. With inductance or capacitance, impedance Z replaces R and apparent power is in VA — not modeled here.

What units should I use?

Volts (V), amperes (A), ohms (Ω), and watts (W). Convert milliamps, kilohms, or kilovolts to these base units first.

Which two values are used if I fill more than two?

The first two non-empty fields from top to bottom (Voltage, Current, Resistance, Power) are treated as the known pair.