UPS Sizing & Runtime Calculator
Add up servers, switches and NAS to get a UPS rating (VA/W) with 25% headroom and the battery energy to ride through an outage.
Electrical load
Total load: 1,290 W
IT equipment with active PFC is typically 0.9–0.99.
5–10 min covers safe shutdown or generator start. Plan 30–60+ min for long outages.
Results
Recommended UPS (standard size)
2 kVA
≈ 1,800 W
Total load
1,290W
Load (VA)
1,358VA
Minimum incl. 25% headroom
1,792VA
Load on recommended UPS
72%
Nominal battery energy needed Estimate
≈ 747 Wh
Equivalent 12 V VRLA blocks: ≈ 7 × 12V 9Ah or 1 × 12V 100Ah
How we calculate
1. Load VA = W ÷ load PF.
2. Minimum VA = max(W × 1.25 ÷ UPS output PF, load VA × 1.25): the UPS must cover both watts and VA with 25% headroom for inrush and growth, then we round up to a standard rating.
3. Battery Wh = W × minutes ÷ 60 ÷ (0.9 inverter efficiency × 0.8 end-of-life ageing × rate factor).
4. Rate factor (VRLA Peukert effect): ~0.45 at 5 min, 0.6 at 15 min, 0.7 at 30 min, 0.78 at 60 min. Fast discharge delivers less than nameplate (20-hour) capacity.
5. Heat roughly halves VRLA battery life for every +10 °C above 25 °C. Keep the UPS room air-conditioned.
These results are estimates to help with planning and budgeting. Our engineers will verify everything on site before final design and equipment proposal.
The same rules of thumb our engineers use for a first design. Good enough for budgeting; the final numbers come from a site survey.
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Open calculatorSend us a floor plan or a few photos of the site
We’ll come back with a few questions, then a first design. The first consultation is free, in Lao, Thai or English, on WhatsApp or our Facebook page.