What Size Online UPS Do I Need? (1kVA to 10kVA Sizing)
Total the load, add headroom, pick the kVA — with a sizing table and worked examples for a server, CCTV and a clinic.
Quick answer
Add up the watts of everything that must stay on, add 20–25% headroom, then pick a UPS whose watt (kW) rating clears that total. Because most online UPS are 0.8 power factor, a 1 kVA unit carries about 800 W — so a ~600 W critical load suits 1 kVA, ~1,200 W suits 2 kVA, and so on up to 10 kVA (8,000 W).
Step 1: list everything that must stay on
Size an online UPS to the critical load only — the things that genuinely cannot blink — not your whole premises. Walk the rack or the counter and write down the running watts of each device. Common online-UPS loads and rough figures:
- A tower or rack server: ~150–400 W each, depending on CPUs and drives.
- A network/storage rack (switches, router, NAS, ONT): ~100–300 W together.
- A CCTV/NVR system (NVR + PoE switch + monitor): ~80–200 W for a typical small site.
- A billing/POS server plus a couple of terminals and a printer: ~200–500 W.
- Clinic instruments (patient monitor, ECG, small analyser): varies — total the nameplate watts.
Sizing rules of thumb
- Size to the UPS's watt (kW) rating, not just its kVA.
- Most Microtek online UPS are 0.8 PF: rated watts ≈ 0.8 × kVA (1 kVA = 800 W, 5 kVA = 4,000 W).
- Add 20–25% headroom over your real load for safety and growth.
- DC bus voltage rises with capacity: ~24–36V at 1 kVA, 72V at 2–3 kVA, 192V at 5.5–10 kVA.
- Capacity sets how much you can run; runtime is set separately by the battery bank.
Step 2: VA vs watts (and why power factor matters)
Appliances are rated in watts (real power); a UPS headline is often in VA (apparent power). They are bridged by the power factor. Most Microtek online UPS are rated at 0.8 power factor, so a 1 kVA unit is good for about 800 W; some newer lithium models like MAX LiFe are unity (kVA = kW). The safe habit is to ignore the kVA marketing number, look at the watt/kW rating, and size your watt total against that.
VA ↔ Watts Converter
InteractiveInverters and UPS are sold in VA, but your appliances are rated in watts. Here's the bridge.
Real power
800 W
Usable wattage you can run.
Rule of thumb
VA × 0.8 ≈ Watts
Keep ~20-30% headroom on top for surge and low mains voltage.
Power factor (PF) is how 'in step' current and voltage are. Indian home inverters are usually quoted at PF 0.8, so a 1000 VA inverter delivers about 800 W. Motors and pumps have a lower PF (more startup surge); pure resistive loads like bulbs are near 1.0.
Convert between watts and VA so you can read your load against a UPS rating
Step 3: add headroom and room to grow
Never run a UPS at its limit. Add 20–25% on top of your real load so the unit runs cool and has reserve, and a little more if you expect to add a server or cameras within a year or two. If anything on the UPS has a motor or compressor (rare on these loads, but it happens in a lab), allow for its startup surge too.
Load to capacity, at a glance
| Real load | Suggested capacity | Typical DC bus | Example use |
|---|---|---|---|
| Up to ~600 W | 1 kVA (800 W) | 24–36V | Single server + network gear, or a CCTV site |
| ~600–1,250 W | 2 kVA (1,600 W) | 72V | Small rack, or a billing/POS cluster |
| ~1,250–1,900 W | 3 kVA (2,400 W) | 72V | Busy rack or a small clinic counter |
| ~1,900–3,500 W | 5–5.5 kVA (4,000–4,400 W) | 192V | Multiple servers / a small server room |
| ~3,500–4,800 W | 6–7.5 kVA (4,800–6,000 W) | 192V | Server room with storage and switches |
| ~4,800–6,400 W | 10 kVA (8,000 W) | 192V | Larger single-phase server/comms room |
Critical load (after headroom) to suggested online UPS
Step 4: runtime — how long must it hold?
Capacity and runtime are two separate decisions. The UPS's internal batteries typically give a few minutes — designed for a clean shutdown or to bridge to a generator. If you need it to actually carry the load through an outage, you add an external VRLA battery bank sized to your target runtime and wired to the UPS's DC bus. The bigger the load and the longer the target, the bigger the bank.
Backup Time Calculator
InteractiveEstimate how long your battery will keep your load running during a power cut.
Estimated backup
3 h 4 min
At this steady load.
Usable energy
918 Wh
1 × 12V × 150Ah × 60% × 85%
If load doubles
1 h 32 min
Backup roughly halves as load rises.
Assumes ~85% inverter efficiency and usable depth-of-discharge of 60% (lead-acid tubular/flat). Real backup depends on battery age, temperature and the exact load running at the time — a tired 3-year-old battery can give 30-40% less. For an exact figure for your home, talk to our team.
Estimate runtime from a battery bank at your load
Worked examples
A small server plus a switch and ONT at about 450 W: add headroom and a 1 kVA E² covers it, with an external bank if you want more than a few minutes. A CCTV/NVR site at ~150 W sits comfortably on a 1 kVA, and a modest external bank can give an hour or more of recording through a cut. A clinic counter running a billing PC, a patient monitor and a small analyser at ~1,000 W suits a 2 kVA, sized with runtime to ride out a typical Delhi outage. Tell us your device list and we will confirm the exact unit and bank.
Where to next
Frequently Asked Questions
How many kVA of online UPS do I need for a server?
Total the running watts of the server and anything on the same UPS, add 20–25% headroom, and pick a unit whose watt rating clears it. A single server with network gear at ~450 W fits a 1 kVA (800 W); a small rack at ~1,000–1,200 W needs a 2 kVA.
Why is a UPS rated in VA when my devices are in watts?
VA is apparent power and watts is real power; power factor links them. Most Microtek online UPS are 0.8 PF, so a 1 kVA unit handles about 800 W. Always size your watt total against the watt/kW rating, not the kVA number.
Does a bigger UPS give longer backup?
Not by itself. The UPS capacity sets how much load you can run; runtime is set by the battery bank. To run longer you add or enlarge an external VRLA battery bank sized to your target, which we configure and install.
Need help choosing?
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