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Watts Volts Amps Calculator

Solve any two of watts, volts, amps, and ohms for the other values—an Ohm’s-law style watt–volt–amp workspace. Runs locally in your browser.

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, with-power, with-R, invalid-domain) · Matrix
Known limitations
  • Resistive DC identities; soft-zero on ÷0
  • Core CVP does not include live graph, viewport, or pointer interaction.
Model
Any two of P, V, I, R → the other two (resistive DC / AC RMS).
Scope
Ohmic resistance; RMS for AC
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
5/5 property · digest 937dea566d45
Legacy regression
17/17 tests · Production surface contract 3/3
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 · 5/5 property · 1/1 cross-interface · 1/1 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.

PowerP = V × I = I²R = V² ÷ R
VoltageV = P ÷ I = I × R = √(P × R)
CurrentI = P ÷ V = V ÷ R = √(P ÷ R)
ResistanceR = V ÷ I = V² ÷ P = P ÷ I²
iFor purely resistive loads, PF = 1 and these formulas apply directly. For AC motors and other inductive loads, use watts to amps (with PF) for current from real power — apparent power is in VA.

How to use

1

Enter any two values

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

2

Read the full set

Results show P, V, I, and R. The first two filled fields (top to bottom) are the known pair.

3

Clear to switch pairs

Use Clear when changing which two quantities you know.

Example calculations

Common configurations with formula and result.

ϟ

10 A · 120 V

Find watts

120 × 10
1200 W
ϟ

15 A · 120 V

Find watts

120 × 15
1800 W
ϟ

20 A · 120 V

Find watts

120 × 20
2400 W
ϟ

Find amps

1200 W · 120 V

1200 ÷ 120
10 A
ϟ

Find volts

240 W · 2 A

240 ÷ 2
120 V
ϟ

With resistance

5 A · 24 Ω

V = 5×24 · P = 120×5
120 V · 600 W

120 V household quick check (P = V × I)

Common values at a glance.

CurrentVoltagePower
10 A120 V1200 W
15 A120 V1800 W
20 A120 V2400 W
5 A240 V1200 W
10 A240 V2400 W
12 V · 5 A—60 W
i Breaker ratings are in amps; appliance labels often list watts. Convert with P = V × I (resistive) before loading a circuit.

Watts Volts Amps 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
Watts (power), volts (potential), amps (current), and ohms (resistance) are linked by Watt’s law P = V × I and Ohm’s law V = I × R. Enter any two values — this calculator finds the other two for DC or resistive AC (RMS). You cannot convert watts to volts (or amps) without a second quantity.
What it calculates
Any two of P, V, I, R → the other two (resistive DC / AC RMS).
Inputs
  • Any two of: power (W), voltage (V), current (A), resistance (Ω)
Outputs
  • Full set: P, V, I, R
Formula
P=V·I; V=I·R; with derived √ forms for P+R pairs
Assumptions
  • Ohmic resistance; RMS for AC
  • First two filled fields define the known pair
Units
  • W, V, A, Ω
Boundary conditions
  • Fewer than two of P,V,I,R → NEEDS_TWO_INPUTS
  • Non-finite → INVALID_NUMBER
  • Division by zero → 0 for the dependent unknown — soft boundary
  • Resistive model only; not for reactive impedance
Example
120 V, 10 A → 1200 W, 12 Ω
Validation cases

13 published on this page · 17/17 tests · Production surface contract 3/3 · View evidence

  • 120 V, 10 A → 1200 W, 12 Ω
  • 1200 W, 120 V → 10 A, 12 Ω
  • 5 A, 24 Ω → 120 V, 600 W
  • 100 W, 400 Ω → 200 V, 0.5 A
  • 600 W, 24 Ω → 120 V, 5 A
  • 240 V, 10 A (2× V) → 2400 W, 24 Ω (linear in V for V+I)
  • 120 V, 20 A (2× I) → 2400 W, 6 Ω
  • 0 V, 10 A → 0 W, 0 Ω (soft: zero divisor → 0)
  • 50 W, 0 Ω → 0 V, 0 A (soft: zero R → 0)
  • 0 W, 12 Ω → 0 V, 0 A
  • Only 120 V (one input) → error NEEDS_TWO_INPUTS
  • Empty inputs → error NEEDS_TWO_INPUTS
  • V=n/a, I=10 → error INVALID_NUMBER
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 watts (P), volts (V), amps (I), and ohms (R) — the calculator solves the rest.

Default check: 120 V · 10 A → 1200 W (and R = 12 Ω).

Supported and not supported

Supported

  • Any two of P, V, I, R → closed {P, V, I, R}
  • Resistive DC / RMS AC (PF ≈ 1)
  • API capability electrical.watt_volt_amp · pin calculation_version: 1.5.1

Not supported

  • Reactive impedance / complex Z
  • Power-factor-aware AC (use watts↔amps / VA tools)
  • Nonlinear device curves

Stable errors: NEEDS_TWO_INPUTS, INVALID_NUMBER.

Core formulas (power triangle)

Find Formula
Watts P = V × I
Amps I = P ÷ V
Volts V = P ÷ I

With resistance (Ohm’s law):

Find Formulas
Volts V = I × R · V = √(P × R)
Amps I = V ÷ R · I = √(P ÷ R)
Ohms R = V ÷ I · R = V² ÷ P · R = P ÷ I²
Watts P = I² × R · P = V² ÷ R

What each unit means

  • Watt (W) — real power (energy per second)
  • Volt (V) — electrical potential / “pressure”
  • Amp (A) — current (charge flow rate)
  • Ohm (Ω) — resistance to current

Tips

  • Convert units first: mA→A (÷1000), kΩ→Ω (×1000), kW→W (×1000).
  • Circuit breakers are rated in amps; many appliances list watts — convert before stacking loads on one circuit.
  • For AC with power factor ≠ 1, use watts to amps instead of I = P/V alone.

Other calculators in this family: Amps to kW Calculator, Amps to VA Calculator, Amps to Volts Calculator, Electric Power Calculator, Energy Consumption Calculator, Energy Cost Calculator, eV to Volts Calculator, kVA to Amps Calculator . Explore all Power & Energy.

→ Amps to kW Calculator Convert amps and volts to real power in kW for DC, AC single-phase, and balanced AC three-phase line-to-line. Runs locally in your browser. Free online tool — no sign-up. › → Amps to VA Calculator Convert amps and volts to apparent power in VA or kVA for single-phase and three-phase circuits. Also convert VA back to amps. Fast and free. › → Amps to Volts Calculator Solve voltage from current and resistance or power using Ohm’s law and P = V × I. Supports resistive DC and RMS AC estimates with clear formulas. › → Electric Power Calculator Calculate electrical power in watts from voltage and current for DC, single-phase AC, or balanced three-phase AC, from current and resistance, or from energy over time. › → Energy Consumption Calculator Estimate energy use in kWh from device watts and hours of operation. Useful for appliance and load planning. Runs locally in your browser. Try it free. › → Energy Cost Calculator Estimate electricity usage cost from watts/hours or kWh and your unit rate. Supports custom billing periods; standing charges and taxes are excluded. Runs locally in your browser. › → eV to Volts Calculator Relate electronvolt energy to electric potential difference through ΔE = qΔV. eV and volts measure different physical quantities. Runs locally in your browser. › → kVA to Amps Calculator Convert kVA and voltage to line current for single-phase and three-phase systems. Uses √3 for three-phase line-to-line volts. Runs locally in your browser. ›
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Frequently asked questions

Key distinctions behind the calculation.

How do I calculate watts from volts and amps?

Multiply: P = V × I. Example: 120 V × 10 A = 1200 W.

How do I find amps from watts and volts?

Divide: I = P ÷ V. Example: 1800 W ÷ 120 V = 15 A.

How do I find volts from watts and amps?

Divide: V = P ÷ I. Example: 240 W ÷ 2 A = 120 V.

Do I need ohms?

Not if you already have two of P, V, and I. Enter resistance when that is what you measured — then V = I × R and P = V × I (or P = I²R).

What is the power triangle?

A mnemonic for Watt’s law: cover one of P, V, or I to see the formula. P = V × I, I = P ÷ V, V = P ÷ I.

Why enter exactly two values?

Four quantities linked by two independent laws need two knowns to determine the rest. The tool uses the first two filled fields top to bottom.

Does this work for AC with power factor?

For resistive AC (PF ≈ 1), yes with RMS volts and amps. For motors and other loads with PF < 1, real power P = V × I × PF (1φ) — use watts to amps for that path.

How is this different from the Ohm's law calculator?

Same physics. This page emphasizes the watts–volts–amps power relationships and household examples; Ohm’s law is the same solver with a resistance-first presentation.