HomeCalculatorsElectricalPower & EnergyWatts to Volts Calculator
Electrical calculator

Watts to Volts Calculator

Find voltage from power and current (or resistance). Useful for DC and resistive AC checks with unit guidance. 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 (w-v-a, w-v-r, v-w, invalid-domain) · Matrix
Known limitations
  • V from P and I, or P and R; reverse P = V·I·PF
  • Core CVP does not include live graph, viewport, or pointer interaction.
Model
Voltage from watts and amps (DC/1φ/3φ) or from watts and ohms; watts from volts and amps.
Scope
RMS quantities for AC
Verification
Engine tested · Source checked · v1.3.1 · CVP VERIFIED · CVP protocol 1.0.0-proposed · Engineering assurance· View Manifest · CVP overview · Specification
Versions
Calculation 1.3.1 · CVP protocol 1.0.0-proposed
CVP identity
0/0 property · digest 21e542929dd0
Legacy regression
13/13 tests · Production surface contract 4/4
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
Not performed
Named expert review
Not performed
CVP suite
3/3 golden · 1/1 CVP boundary · 1/1 invalid · 1/1 cross-interface · 4/4 CVP contract · Manifest
Sources
Sources
Evidence
13 legacy golden · legacy regression suite · 3/3 oracle-backed golden · 1/1 invalid · Artifact integrity PASS
This calculator CURRENT · Public schema 1.3.1 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.

DC (with amps)V = P ÷ I
AC 1φV = P ÷ (I × PF)
AC 3φ (L-L)V = P ÷ (√3 × I × PF)
AC 3φ (L-N)V = P ÷ (3 × I × PF)
With ohms / impedanceV = √(P × R)
Volts → watts (DC)P = V × I
iFor DC or resistive AC, use single phase and PF = 1. Three-phase watts→volts returns line-to-line RMS. The ohms tab also covers RF-style V = √(P×Z) when Z is in ohms (e.g. 50 Ω).

How to use

1

Choose path

W → V (amps) for power and current; W → V (ohms) for power and resistance; V → W to reverse.

2

Enter values and circuit type

For AC with amps, set PF and single/three phase. For DC, PF = 1 and single phase.

3

Read volts or watts

Three-phase amps path returns line-to-line voltage.

Example calculations

Common configurations with formula and result.

ϟ

DC · 20 W · 4 A

V = P ÷ I

20 ÷ 4
5 V
ϟ

240 W · 2 A

Default DC check

240 ÷ 2
120 V
ϟ

AC 1φ · 1300 W · 12 A · PF 0.9

With power factor

1300 ÷ (12 × 0.9)
120.37 V
ϟ

From resistance

40 W · 10 Ω

√(40 × 10)
20 V
ϟ

RF · 100 mW · 50 Ω

Enter 0.1 W

√(0.1 × 50)
2.236 V
ϟ

Volts → watts

120 V · 2 A · PF 1

120 × 2
240 W

Quick V = P ÷ I (PF = 1)

Common values at a glance.

PowerCurrentVoltage
20 W4 A5 V
60 W5 A12 V
120 W10 A12 V
240 W2 A120 V
1000 W8.333 A120 V
40 W · 10 Ω—20 V (√ path)
i For AC, divide by PF as well (and √3 for three-phase L-L). Ohms path: V = √(P×R).

Watts to Volts calculator specification

Version 1.3.1 · Engine tested

Calculation status

Review policy · Evidence

Definition
You cannot convert watts to volts from power alone — you also need current (amps) or resistance/impedance (ohms). With current: DC V = P/I; AC 1φ V = P/(I×PF); AC 3φ L-L V = P/(√3×I×PF). With resistance: V = √(P×R). This tool also reverses volts × current → watts.
What it calculates
Voltage from watts and amps (DC/1φ/3φ) or from watts and ohms; watts from volts and amps.
Inputs
  • Power P (W) and current I (A), optional PF and phase → V
  • Power P (W) and resistance R (Ω) → V
  • Voltage V and current I, optional PF and phase → W
Outputs
  • Voltage in V, or power in W
Formula
V=P/(√3 (3φ only)·I·PF); V=√(P·R); P=√3 (3φ only)·V·I·PF
Assumptions
  • RMS quantities for AC
  • Balanced three-phase when √3 selected
  • Ohms path assumes real resistive (or |Z| for RF magnitude)
Units
  • W, A, PF → V
  • W, Ω → V
Boundary conditions
  • Amps path (phase-quotient): zero current (b) → 0 V — soft
  • Zero power (a) on amps path → 0 V
  • PF ≤ 0 on amps/reverse watts paths treated as PF = 1 (engine: pf > 0 ? pf : 1) — soft
  • Ohms path (sqrt-product): negative P×R clamped to 0 under √ — soft
  • Zero P or R on ohms path → 0 V
  • Engine does not hard-reject PF outside (0,1]; document PF ∈ (0,1] for physical AC use
Example
240 W, 2 A, PF 1 → 120 V
Validation cases

15 published on this page · 13/13 tests · Production surface contract 4/4 · View evidence

  • 20 W, 4 A, DC → 5 V
  • 240 W, 2 A, PF 1, 1φ → 120 V
  • 1300 W, 12 A, PF 0.9, 1φ → ≈120.37 V
  • 40 W, 10 Ω → 20 V
  • 0.1 W, 50 Ω → ≈2.236 V
  • 120 V, 2 A, PF 1 → W → 240 W
  • 1000 W, 10 A, PF 0.8, 3φ → ≈72.17 V
  • 480 W, 2 A, PF 1 (2× P) → 240 V (linear in P)
  • 240 W, 1 A, PF 1 (half I) → 240 V (inverse in I)
  • 240 W, 0 A, PF 1 → 0 V (soft: zero current → 0)
  • 0 W, 2 A, PF 1 → 0 V
  • 240 W, 2 A, PF 0 → 120 V (soft: PF≤0 treated as 1)
  • -10 W, 10 Ω → 0 V (soft: negative P×R → √0)
  • 0 W, 10 Ω → 0 V
  • 240 W → 120 V → W round-trip at PF 1 → 240 W
Sources
  • Watt’s law / power identity — Real power P = V × I × PF (1φ); P = √3 × V × I × PF (3φ L-L)
    Supports: V = P/(I·PF); P = V·I·PF; 3φ with √3
  • Resistive power identity — P = V²/R ⇒ V = √(P·R)
    Supports: W → V (ohms) / RF |Z| magnitude path
  • IEC 60050 — International Electrotechnical Vocabulary — Active power (IEV 131-11-42) · accessed 2026-09-05
    Supports: P is active power; unit watt (W). Watts-path voltage uses P, not apparent power S.
  • IEC 60050 — International Electrotechnical Vocabulary — Power factor (IEV 131-11-46) · accessed 2026-09-05
    Supports: λ = |P| / S; AC watts path V = P / (I·λ) (1φ) or V = P / (√3·I·λ) (3φ L-L)
  • IEEE Std 1459-2025 — Power factor in AC real-power calculations · 2025-05-16 · errata checked · accessed 2026-09-05
    Supports: PF scaling on amps and reverse watts paths
  • BIPM SI Brochure (9th edition, version 4.01) — SI units for ampere, volt, ohm, and watt · 2026-06 · DOI · accessed 2026-09-05
    Supports: DC V = P/I; V = √(P·R) from P = V²/R
  • NIST Guide to the SI (SP 811) — Volt, ampere, ohm, watt
    Supports: SI unit relationships for V, A, Ω, W
Calculation version
1.3.1

Background

Interpretation and common distinctions.

Convert watts to volts using current or resistance. Power alone is not enough.

Default (amps path): 240 W ÷ 2 A = 120 V.

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Frequently asked questions

Key distinctions behind the calculation.

How do I convert watts to volts?

Divide power by current: V = P ÷ I for DC. For AC single-phase use V = P ÷ (I × PF). For three-phase line-to-line use V = P ÷ (√3 × I × PF). Or if you know resistance: V = √(P × R).

Can I convert watts to volts without amps?

Not with the amps formula. You need either current or resistance/impedance. Watts alone are not enough.

How do I handle AC power factor?

Use the W → V (amps) tab, set PF, and choose single or three phase. Resistive loads: PF = 1.

What about three-phase?

Select three phase on the amps tab. The result is line-to-line RMS voltage. Line-to-neutral: V = P ÷ (3 × I × PF).

When do I use the ohms formula?

When you know power and resistance (or characteristic impedance Z). V = √(P × R). Common for resistive heaters and RF systems (e.g. 50 Ω).

How do I convert volts back to watts?

Use V → W: P = V × I for DC; multiply by PF (and √3 for 3φ) for AC real power.

Is milliwatt RF supported?

Yes on the ohms tab — convert mW to watts first (100 mW = 0.1 W). Example: √(0.1 × 50) ≈ 2.236 V.