Formula
Single phase: I (A) = S (VA) ÷ V
Three phase: I (A) = S (VA) ÷ (√3 × VL-L)
Worked example
A 1,000 VA (1 kVA) UPS on a 230 V supply: I = 1000 ÷ 230 = 4.35 A maximum input current at full load.
Reference table
Quick reference (single phase)
| VA | Amps @ 120 V | Amps @ 230 V |
|---|---|---|
| 100 | 0.83 | 0.43 |
| 500 | 4.17 | 2.17 |
| 1,000 | 8.33 | 4.35 |
| 2,000 | 16.67 | 8.7 |
| 5,000 | 41.67 | 21.74 |
| 10,000 | 83.33 | 43.48 |
Where this shows up in the real world
Every UPS under a desk is rated in VA, and the question is always the same: how much can it actually carry? A 1500 VA unit on a US 120 V supply handles 12.5 A of apparent load — but check the watt rating too, because a 1500 VA / 900 W UPS dies at 900 W of computers regardless of the VA math.
Common mistakes to avoid
The UPS double-rating trips people constantly: stay under both the VA and the W limits. The other error is sizing a UPS to the nameplate of every device plugged in — nameplates are maximums; measured draw of a desktop setup is often half. Measure, convert, then buy runtime.
Frequently asked questions
VA vs watts — which does my UPS rating mean?
UPS units carry both ratings. VA limits the current; watts limit the real power. Stay under both: a 1000 VA / 600 W UPS cannot run a 700 W load.
Is 1 kVA just 1000 VA?
Yes — kVA is simply thousands of volt-amps. Use our kVA to amps tool for larger equipment.
Why do transformers use VA ratings?
Transformer heating depends on current, which tracks apparent power (VA) regardless of the load's power factor.