Power · VA · Power Factor
Watts to VA Converter
Convert watts ↔ volt-amperes with real power-factor math. Solve a measured PF in the Power Factor Lab, look up typical device PFs, and size a UPS or generator with honest headroom — no signup, no server.
0.80
Apparent power
625
VA · 0.625 kVA
0.80
Real power
1,200
W · usable output
Apparent power (DC)
800
VA = W (PF ≡ 1)
Power factor
0.8000
Reactive power
375 VAR
Phase angle φ
36.87°
0.90
+25%
Required
1,667 VA
Buy at least
2,000 VA
01Typical power factor by device
Tap a device to load its typical power factor into the converter. These are honest typical ranges — a nameplate PF is measured at full load, and motors at half load can be much worse. For critical sizing, measure or use the most pessimistic end of the range.
02Worked examples (hand-verified)
Every number below was computed by hand from the formulas in the methodology — and re-checked by the page's own test suite against an independent Python oracle.
🖥️ Gaming PC + monitor: 500 W @ PF 0.8
VA = W ÷ PF
500 ÷ 0.8 = 625 VA
With 25% headroom: 625 × 1.25 = 781 VA → buy a ≥1000 VA UPS.
500 ÷ 0.8 = 625 VA
With 25% headroom: 625 × 1.25 = 781 VA → buy a ≥1000 VA UPS.
✓ 625 VA · UPS class 1000 VA
🏭 Workshop: 3000 W generator sizing
Mixed-load PF ≈ 0.8, headroom 25%:
3000 ÷ 0.8 = 3750 VA
3750 × 1.25 = 4687.5 VA → a 5 kVA generator is the right class. Check motor starting surge separately.
3000 ÷ 0.8 = 3750 VA
3750 × 1.25 = 4687.5 VA → a 5 kVA generator is the right class. Check motor starting surge separately.
✓ 4687.5 VA · 5 kVA genset
🔋 1500 VA UPS — how many real watts?
W = VA × PF (UPS output PF):
at PF 0.8: 1500 × 0.8 = 1200 W
at PF 0.9: 1500 × 0.9 = 1350 W
Reverse: a 1200 W server @ PF 0.9 needs 1200 ÷ 0.9 = 1333 VA → 1500 VA UPS.
at PF 0.8: 1500 × 0.8 = 1200 W
at PF 0.9: 1500 × 0.9 = 1350 W
Reverse: a 1200 W server @ PF 0.9 needs 1200 ÷ 0.9 = 1333 VA → 1500 VA UPS.
✓ 1200 W / 1350 W · needs 1333 VA
03Methodology
- Scope: this page covers the full watts to VA conversion workflow — forward (W→VA), reverse (VA→W), DC mode, PF lab, and UPS/generator sizing — with every formula shown next to its result.
- Forward:
VA = W ÷ PF. Example: 500 W ÷ 0.8 = 625 VA. - Reverse:
W = VA × PF, where PF is the source (UPS/generator) rating. Example: 1500 VA × 0.8 = 1200 W. - PF lab:
PF = W ÷ VA; reactive powerVAR = √(VA² − W²); phase angleφ = arccos(PF). Example: 500 W, 625 VA → VAR = 375, φ = 36.87°. - DC honesty: PF is locked to 1 because apparent power is an AC concept — with DC there is no phase shift and no reactive power, so VA ≡ W numerically.
- Sizing:
required VA = total W ÷ PF × margin, then round UP to the nearest standard commercial rating (500, 650, 800, 850, 1000, 1100, 1200, 1500, 2000, 2200, 3000, 5000, 6000, 8000, 10000, 20000 VA). Never round down. - Validation: PF outside (0, 1], negative powers, or W > VA are rejected as invalid — the page shows an error instead of computing nonsense.
- Display: inputs in kW/kVA are scaled ×1000 before the math; results show 4 significant decimals trimmed of trailing zeros with thousand separators.
04Honest limitations
- Nameplate PF ≠ measured PF. Motor PF collapses at light load — a 0.85 nameplate motor at 30% load can sit near 0.5. Size with the worst realistic case, not the brochure.
- Steady state only. Induction motors draw 3–7× running current at startup; the sizer does not model inrush — check locked-rotor kVA separately for motor-heavy loads.
- Leading PF is out of scope. Capacitive/leading loads (rare outside industrial correction banks) use the same triangle, but the lab assumes lagging convention.
- Not billing advice. Utilities penalize low PF for industrial customers; correcting it needs a proper power-quality study, not a web calculator.
- Harmonics. Switching supplies distort current waveform — their "PF" is displacement × distortion; the single-number model is an approximation.
05When to use a different tool
⚡ Need amps or volts?
Converting amps ↔ watts/kW (which needs voltage and phase) is current math, not PF math.
→ amps-to-kW calculator
Converting amps ↔ watts/kW (which needs voltage and phase) is current math, not PF math.
→ amps-to-kW calculator
🔥 Need energy (kJ, kWh)?
Watts and VA are power (rate). For energy over time, convert properly.
→ kW to kJ converter
Watts and VA are power (rate). For energy over time, convert properly.
→ kW to kJ converter
🔌 General electrical units?
Volts, amps, ohms, and unit prefixes in one place.
→ electrical unit converter
Volts, amps, ohms, and unit prefixes in one place.
→ electrical unit converter
06Frequently asked questions
Answers are identical in the visible FAQ and the machine-readable FAQ schema.
What is the formula to convert watts to VA?
VA = Watts ÷ Power Factor. Apparent power (VA) is always equal to or larger than real power (watts) because power factor is between 0 and 1. Example: a 500 W load with a power factor of 0.8 needs 500 ÷ 0.8 = 625 VA. This tool does the division for you and works both ways.
How do I convert watts to VA step by step?
1) Find the load in watts (nameplate or measured). 2) Find the power factor (nameplate, typical-device table, or measured with a power meter). 3) Divide: VA = W ÷ PF. Example: 500 W ÷ 0.8 = 625 VA. 4) For a UPS or generator, add a 20–25% headroom margin and round UP to the nearest standard rating — here 625 × 1.25 = 781 VA, so pick a ≥1000 VA unit.
How do I convert VA to watts?
Watts = VA × Power Factor. The power factor is the rating of the SOURCE (UPS/generator), not the load. Example: a 1500 VA UPS with a 0.8 output power factor delivers 1500 × 0.8 = 1200 W of real power; the same 1500 VA with a 0.9 PF delivers 1350 W. Check your UPS nameplate for its output PF.
What is power factor (PF) in simple terms?
Power factor is the fraction of apparent power that actually does useful work: PF = Watts ÷ VA, always between 0 and 1. A PF of 1.0 (resistive loads like heaters) means all current does work; a PF of 0.7 means 30% of the current just sloshes back and forth as reactive power (VAR) without doing work — but your UPS, generator, and wiring must still be sized for the full VA.
What is a typical power factor for common devices?
Resistive loads (kettle, toaster, incandescent bulb): ~1.0. LED lights/TV: ~0.9. Laptop and phone chargers: 0.5–0.7 without power-factor correction, 0.9+ with active PFC. Desktop PC PSU (80+ with PFC): 0.9–0.98. Refrigerator, washing machine, power tools (motors): 0.6–0.9. These are TYPICAL values — actual PF varies with load and design, so for sizing critical equipment measure or use the most pessimistic value.
How do watts to VA work for DC circuits?
For DC, power factor is always exactly 1, so watts = VA numerically — a 800 W DC load is 800 VA. Honestly, 'apparent power' is an AC concept: with DC there is no phase shift and no reactive power, so the distinction collapses. This tool locks PF to 1 in DC mode rather than pretending the conversion means something.
How do I find the power factor of my device?
Three ways, from best to roughest: 1) Measure with a plug-in power meter (Kill-A-Watt style) — it shows watts and VA directly, PF = W ÷ VA. 2) Read the nameplate or datasheet (many PSUs and UPS units list it). 3) Use the typical-device table above as an estimate. Honest limitation: a nameplate PF is measured at full load — motors at half load can have much worse PF than their rating.
How many watts is a 1500 VA UPS?
It depends on the UPS output power factor printed on its nameplate: 1500 VA × 0.8 = 1200 W; 1500 VA × 0.9 = 1350 W. Never assume a VA number is watts — budget UPS units are often rated at 0.6 PF, so a '1000 VA' unit may only deliver 600 W. Size your load to the WATTS rating, not the VA rating.
What size UPS do I need for my load?
Add up the watts of everything the UPS must carry, divide by the lowest load power factor, then add 20–25% headroom: required VA = total W ÷ PF × 1.25. Round UP to a standard size. Example: 1200 W of mixed gear at PF 0.9 → 1200 ÷ 0.9 × 1.25 = 1667 VA → buy a 2000 VA UPS. The sizer tab above does this math and recommends the next standard rating.
What size generator do I need for a 3000 W load?
Convert to VA first, then add headroom: 3000 W ÷ 0.8 (typical mixed-load PF) = 3750 VA, × 1.25 headroom = 4687 VA — so a 5 kVA generator is the right class. Also check motor starting surge (3–7× running watts for induction motors), which can demand a bigger unit than the steady-state math suggests.
Is VA the same as watts?
No — they are equal ONLY when power factor is 1.0 (purely resistive DC or AC loads). For anything with motors, transformers, or switching power supplies, VA is larger than watts. Saying 'a 2000 W generator' when you mean '2000 VA' understates the real capacity by the power factor — a classic and expensive sizing mistake.
Why is VA always greater than or equal to watts?
Because VA = W ÷ PF and PF can never exceed 1, dividing by a number ≤ 1 can only make the result bigger (or equal at PF = 1). Geometrically, watts are the adjacent side of the power triangle and VA is the hypotenuse — the hypotenuse is never shorter than a leg. The leftover is reactive power (VAR), the opposite leg.
Can power factor be greater than 1 or negative?
No. For passive loads PF is between 0 and 1 by definition (it is the cosine of the phase angle, or more generally real ÷ apparent power). A 'PF' above 1 means someone mixed up units or misread the meter — this tool rejects PF > 1 as invalid input rather than computing nonsense.
What is the difference between kVA and kW?
Only scale: 1 kVA = 1000 VA and 1 kW = 1000 W, and the same PF relationship holds: kVA = kW ÷ PF. Generators and transformers are rated in kVA (what they must carry); loads consume kW (what does work). A '5 kVA' generator at 0.8 PF delivers 4 kW — marketing that blurs this is why the worked examples on this page matter.
When should I NOT use this watts-to-VA converter?
When you need current or voltage math: converting amps ↔ watts/kW (needs voltage and phase) belongs to our amps-to-kW calculator. When you need ENERGY (kWh, joules, kJ) rather than power, use the kW-to-kJ converter. For general electrical unit conversion (V, A, Ω), use the electrical unit converter. This tool owns exactly one job: the watts ↔ VA ↔ power-factor triangle.
Is my data private when I use this calculator?
Yes. This page is 100% client-side: every calculation runs in your own browser with zero network requests — no analytics, no fonts, no CDNs. Your wattage, device list, and sizing inputs never leave your device. You can verify this by opening the page with your network disconnected.