kW to VA Calculator
Convert kilowatts to volt-amps using the load's power factor. Apparent power is always equal to or greater than real power.
Common conversions
| Input | Result |
|---|---|
| 0.5 kW @ PF 1.0 | 500 VA |
| 1 kW @ PF 0.9 | 1,111.11 VA |
| 2.5 kW @ PF 0.8 | 3,125 VA |
| 3 kW @ PF 0.85 | 3,529.41 VA |
| 5 kW @ PF 0.95 | 5,263.16 VA |
| 7.5 kW @ PF 0.8 | 9,375 VA |
| 10 kW @ PF 0.9 | 11,111.11 VA |
The math behind it
- VA = kW × 1000 / PF
- VA = 2.5 × 1000 / 0.8
- VA = 3,125
Everything you need to know
Knowing a device's real-power draw in kW isn't enough to pick a UPS, inverter, or generator. Those products are rated by how much apparent power, in VA, they can supply, and that number is always equal to or larger than the kW figure you started with.
How the kW to VA formula works
Kilowatts represent real power, the energy that does actual work: heating an element, spinning a motor, or lighting an LED. Volt-amps represent apparent power, the full combination of voltage and current the source must be able to supply, including the reactive share that never converts into usable output. Dividing kW by PF and multiplying by 1000 reverses the kW-from-VA calculation, so it always scales the number up whenever PF is below 1.0. A PF of 0.5, common on older non-PFC electronics, doubles the VA requirement compared to the kW figure alone, meaning a 1 kW load needs a source capable of supplying 2,000 VA.
Why sizing by kW alone undersizes equipment
A UPS, inverter, or small generator has a fixed current-handling limit built into its transformer windings and switching components, and that limit is expressed in VA because it doesn't depend on what the connected load's power factor happens to be. If a buyer picks a 1,000 VA UPS to support what they believe is a 1,000 W load, and that load actually runs at PF 0.7, the true apparent-power demand is about 1,429 VA, already 43% over the unit's rated capacity. The UPS will alarm or shut down well before the connected devices reach their rated wattage, because the current draw crossed the VA limit first. Converting kW to VA before shopping avoids that mismatch entirely.
Worked scenario: choosing a UPS for a home office
A home office setup, including a desktop computer, two monitors, and a printer, draws a measured 2.5 kW of real power, and the combined power factor of that equipment mix comes out to 0.8, typical for a blend of switch-mode supplies. Dividing 2.5 kW by 0.8 and multiplying by 1000 gives 3,125 VA of required apparent power. Buying a UPS rated for only 2,500 VA, on the mistaken assumption that watts and VA track closely, would leave the unit 625 VA short of what the load actually demands, risking an overload alarm during a brief power dip.
Common applications
Convert your equipment's kW draw to VA before comparing UPS datasheets, since capacity limits are set by apparent power, not watts alone.
Battery backup systems are sold by VA capacity. Converting a laptop, router, and monitor's combined kW load to VA shows how many devices a given unit can actually support.
Server room power distribution units list VA limits per outlet strip. Converting rack kW loads to VA at the equipment's PF avoids tripping a shared circuit.
Sensitive electronics need apparent-power headroom, not just wattage. Converting the kW draw of chargers and adapters to VA at a realistic PF prevents nuisance shutdowns.
Common mistakes
A UPS or inverter's real limit is apparent power. Shopping by watt rating alone can leave 20-40% less capacity than the VA figure suggests, depending on PF.
Non-PFC power supplies commonly run PF 0.5-0.7. Assuming unity PF understates the required VA by a wide margin for exactly this kind of load.
A calculated VA result smaller than the kW input means a power factor greater than 1.0 was entered, which isn't physically possible and signals a data-entry error.
Motors, compressors, and some power supplies draw a brief surge well above their steady-state VA on startup. Sizing to the calculated steady-state figure alone can trip protective circuits at power-up.
Frequently asked questions
Why is VA always equal to or greater than kW?+
Because power factor is between 0 and 1, and dividing by a number at or below 1 gives a result at or above the original. VA only equals kW when PF is exactly 1.0.
What PF should I assume if the equipment's PF is unknown?+
0.8 is a reasonable default for mixed office or household electronics. Motor-heavy loads run closer to 0.7, while equipment with active power factor correction can reach 0.95 or higher.
How many VA is a 5 kW load?+
5,263 VA at PF 0.95, or 6,250 VA at PF 0.8. The exact figure depends on the connected equipment's actual power factor, so check the nameplate whenever possible.
Does a lower PF always mean I need a bigger UPS?+
Yes, a lower PF always increases the required VA for the same kW load. Dropping PF from 0.9 to 0.6 on a 2 kW load raises the requirement from about 2,222 VA to 3,333 VA.
Can I just buy a UPS rated in watts instead of VA?+
Yes, if the watt rating is clearly listed, but confirm it already reflects the manufacturer's assumed PF. Many budget UPS units only print VA, which is why converting your kW load to VA first prevents an undersized purchase.
Is the kW to VA conversion different for three-phase loads?+
No, the VA = kW × 1000 / PF relationship is the same regardless of phase count. Phase and voltage only come into play if you also need to calculate current.
Why do two loads with the same kW need different VA capacity?+
Because their power factors differ. A 3 kW resistive heater needs 3,000 VA, while a 3 kW motor at PF 0.75 needs 4,000 VA of apparent-power capacity for the identical real-power output.
Should I round the VA result up when buying equipment?+
Yes, round up to the next standard VA size and add 15-20% headroom. That margin covers motor inrush current and future load growth without immediately maxing out the unit.
Does this formula apply to solar inverters too?+
Yes, inverter output capacity is rated in VA for the same reason as generators and UPS units. A 4 kW inverter output at PF 0.9 still requires about 4,444 VA of downstream conductor and breaker capacity.