UPS sizing calculator
How big a UPS do you actually need?
Add the devices you want to protect, set the headroom, and we'll size the UPS in kVA, round up to a standard rating, and recommend a topology. Methodology follows the same load schedule we use on commissioned site assessments.
Step 1 · Connected load
| Device / load | Watts ea. | Qty | Subtotal | |
|---|---|---|---|---|
| 1,400 W | ||||
| Connected load | 1,400 W | |||
+ Common devices
Step 2 · Sizing assumptions
Allowance for growth and inrush. 25% is the industry default; raise for high-growth or motor loads.
Real-power to apparent-power ratio. 0.9 is conservative for mixed IT loads; modern PSUs are 0.95-0.99.
Result
Required UPS
1.9 kVA
Equivalent to 1,944 VA at 0.90 pf
Round-up size
2 kVA
Nearest standard UPS rating you can specify off-the-shelf
Recommended topology
Online double-conversion
Mid-range commercial load. Online double-conversion provides full input/output isolation and is the appropriate choice for server rooms, healthcare and PoS estates.
Our engineers will validate the calculation against your site (inrush, harmonics, redundancy class) and return a fully scoped proposal within one business day.
Methodology
How the calculation works
1. Connected load. We sum the watts and quantity for every device. Watts is the real (active) power the device consumes — most modern equipment nameplates state Watts directly.
2. Headroom. 25% is the industry default. It covers PSU inrush at startup, planned growth over the UPS service life, and the gap between nameplate and steady-state draw.
3. Power factor conversion. Watts is real power; UPS systems are rated in VA (apparent power). Converting at a conservative 0.9 power factor sizes for mixed loads. Modern PSUs run 0.95-0.99 and can be sized tighter.
4. Round-up to a standard rating.We round up to the nearest standard UPS size — there is no point specifying a custom 7.4 kVA UPS when a 10 kVA off-the-shelf unit is cheaper and gives you more growth headroom.
5. Topology. Sub-1.5 kVA loads on clean utility power are fine on line-interactive UPS. Above that — and any mission-critical or healthcare load — needs online double-conversion.
What we don't model. Inrush from motors, compressors, laser printers, harmonic content, and battery runtime (separate calculator). Always validate with a site survey before buying.