HomeCalculatorsElectricalPower & EnergyWatts to VA Calculator
Electrical calculator

Watts to VA Calculator

Convert real power in watts to apparent power in VA using power factor. Clarifies W vs VA for sizing breakers and transformers. Try it free.

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 · 3/3 declared partitions (w-va, va-w, invalid-domain) · Matrix
Known limitations
  • Sinusoidal PF; optional factor scales result
  • Core CVP does not include live graph, viewport, or pointer interaction.
Model
Apparent power in VA from real power in watts and PF, or watts from VA and PF.
Scope
PF in (0, 1] — required (not optional)
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
5/5 property · digest c927268aa5e1
Legacy regression
16/16 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
2/2 golden · 2/2 CVP boundary · 2/2 invalid · 5/5 property · 1/1 cross-interface · 4/4 CVP contract · Manifest
Sources
Sources
Evidence
9 legacy golden · 2 legacy boundary · legacy regression suite · 2/2 oracle-backed golden · 2/2 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.

Watts → VAVA = W ÷ PF
VA → wattsW = VA × PF
Power factorPF = W ÷ VA
To kilovolt-ampereskVA = VA ÷ 1000 = W ÷ (1000 × PF)
iPF is dimensionless, typically 0–1. At PF = 1, VA = W. For mixed household loads, PF ≈ 0.8 is a common estimate. Phase is not in this conversion — use amps tools when you need current from voltage.

How to use

1

Choose Watts → VA or VA → Watts

Forward mode needs real power; reverse needs apparent power.

2

Enter power and power factor

Prefer nameplate PF. If unknown, use 0.8 for mixed loads or 0.6–0.7 for heavy motors / older gear.

3

Read VA or watts

Select UPS/inverter/generator VA with headroom above the calculated value.

Example calculations

Common configurations with formula and result.

ϟ

1000 W · PF 0.8

Default check

1000 ÷ 0.8
1250 VA
ϟ

UPS example

500 W · PF 0.67

500 ÷ 0.67
≈ 746 VA (use ≥ 750 VA)
ϟ

Unity PF

1000 W · PF 1

1000 ÷ 1
1000 VA
ϟ

VA → watts

1250 VA · PF 0.8

1250 × 0.8
1000 W
ϟ

Inverter loads

3200 W · PF 0.8

3200 ÷ 0.8
4000 VA

Watts → VA for 1000 W by PF

Common values at a glance.

Power factorVA for 1000 WTypical loads
1.01000 VAHeaters, incandescent
0.91111 VAMotors full load / modern PSU
0.81250 VAMixed household / genset default
0.71429 VAMotor-heavy
0.61667 VAComputers / older UPS loads
i Lower PF → more VA for the same watts. Wire and breaker current follow VA, not watts alone.

Watts to VA calculator specification

Version 1.3.1 · Engine tested

Calculation status

Review policy · Evidence

Definition
Volt-amperes (VA) measure apparent power; watts (W) measure real power. They are linked by power factor: VA = W ÷ PF and W = VA × PF. Voltage and phase are not required once you know watts (or VA) and PF. UPS, inverters, and many generators are sized in VA — always convert watts through PF before selecting equipment.
What it calculates
Apparent power in VA from real power in watts and PF, or watts from VA and PF.
Inputs
  • Real power P (W) and PF → VA
  • Apparent power S (VA) and PF → W
Outputs
  • VA or watts
Formula
VA=W/PF; W=VA·PF
Assumptions
  • PF in (0, 1] — required (not optional)
  • No voltage/phase required once P (or S) and PF are known
Units
  • W, PF → VA
Boundary conditions
  • PF ≤ 0 or > 1 → POWER_FACTOR_OUT_OF_RANGE
  • Missing PF → MISSING_REQUIRED_INPUT
  • Zero watts/VA with valid PF → 0
  • API: mode w-va|va-w; a|P|S; b|power_factor; optional factor
Example
1000 W, PF 0.8 → 1250 VA
Validation cases

12 published on this page · 16/16 tests · Production surface contract 4/4 · View evidence

  • 1000 W, PF 0.8 → 1250 VA
  • 500 W, PF 0.67 → ≈ 746.27 VA
  • 1000 W, PF 1 → 1000 VA
  • 1250 VA, PF 0.8 → W → 1000 W
  • 2000 W, PF 0.8 (2× watts) → 2500 VA (linear in W)
  • 1000 W, PF 0.4 (half PF) → 2500 VA (inverse in PF)
  • 0 W, PF 0.8 → 0 VA
  • 1000 W, PF 0 → error POWER_FACTOR_OUT_OF_RANGE
  • 5000 W, PF 0.9 → ≈5555.56 VA
  • 2500 VA, PF 0.8 → W → 2000 W
  • missing PF → error MISSING_REQUIRED_INPUT
  • 1000 W → VA → W round-trip at PF 0.8 → 1000 W
Sources
Calculation version
1.3.1

Background

Interpretation and common distinctions.

Convert watts (real power) to volt-amperes (apparent power) using power factor (required):

S((VA)) = (P((W)))/PF P((W)) = S((VA)) × PF

Default example: 1000 W · PF 0.8 → 1250 VA.

Supported and not supported

Supported

  • Watts → VA and VA → watts with PF in (0, 1]
  • API engine watts-va (tool id watts-to-va); roadmap op real_from_S_pf / apparent_from_P_pf
  • Capability id: electrical.watts_to_va (model: electrical.active_power_from_apparent_power)

Not supported

  • Treating VA ≈ W without PF
  • Voltage/current → VA (use Amps→VA)
  • Unbalanced / harmonic power (IEEE 1459 full)

Agent / API notes

Pin calculation_version: 1.3.1. Stable errors: MISSING_REQUIRED_INPUT, INVALID_NUMBER, VALUE_MUST_BE_NON_NEGATIVE, POWER_FACTOR_OUT_OF_RANGE, INVALID_MODE.

Legacy body fields a / b still work; prefer P|S and power_factor.

Watts vs VA

Watts (W) VA
Measures Real / active power Apparent power
Use for Energy, heat, work done Equipment ratings, current capacity
Relation P = S × PF S = P / PF

At PF = 1, VA equals watts. Lower PF means more VA (and more current) for the same watts.

Why convert?

  • UPS / inverter / generator nameplates are often in VA or kVA
  • Breakers and wire must handle current from apparent power
  • Power factor correction planning starts from W vs VA

Rule of thumb for mixed loads: multiply watts by 1.25 (same as PF = 0.8).

Typical power factor

Load Typical PF VA for 1000 W
Resistive heater / incandescent 0.95–1.0 ~1000–1053 VA
Computers / office gear 0.6–0.8 1250–1667 VA
Induction motor (full load) 0.8–0.9 1111–1250 VA
Induction motor (light load) 0.2–0.7 much higher VA
Mixed household (estimate) 0.8 1250 VA

Tips

  • Always convert before picking VA-rated gear — a 5000 W load is not a 5000 VA inverter unless PF = 1.
  • Prefer conservative PF (0.7–0.8) when the exact value is unknown.
  • For kVA results: kVA = VA / 1000, or use watts to kVA.

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Frequently asked questions

Key distinctions behind the calculation.

How do I convert watts to VA?

Divide real power by power factor: VA = W ÷ PF. Example: 1000 W ÷ 0.8 = 1250 VA.

How do I convert VA to watts?

Multiply: W = VA × PF. Example: 1250 VA × 0.8 = 1000 W.

What is the difference between watts and VA?

Watts are real power that does work or becomes heat. VA is apparent power (RMS volts × amps) and includes reactive power. They are equal only when PF = 1.

What power factor should I use?

Prefer nameplate or measured PF. Resistive ≈ 1; mixed household ≈ 0.8; motors often 0.6–0.9; some IT/UPS loads ≈ 0.6–0.7. When unsure, 0.8 is a common conservative estimate.

Why size UPS and inverters in VA?

They must supply apparent power — both real and reactive. A 1000 W load at PF 0.8 needs 1250 VA capacity, not a 1000 VA unit.

Do I need voltage or phase?

Not for watts ↔ VA when PF is known. Voltage matters when converting VA to amps (I ≈ VA / V for single-phase).

How is VA related to kVA?

1 kVA = 1000 VA. So kVA = W ÷ (1000 × PF). Use watts to kVA for kilovolt-amp results.

Does VA determine wire and breaker size?

Current follows apparent power. Using watts alone underestimates amps when PF < 1 — convert to VA first, then to amps.