Size the UPS and battery bank before you request a quote.
Enter the real load and the backup time. The calculator converts kW to kVA, applies a design margin, and estimates the 12 V battery blocks required for a VRLA string.
Input
kW
Runtime
minutes
Output
kVA + Ah
Recommended configuration
Step 2Nearest standard size
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Design kVA: —
12 V blocks
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Battery sizing assumes VRLA, 0.9 inverter efficiency, 0.6 usable depth of discharge, and a 1.25 design margin. Confirm with the final model datasheet.
This is a first-pass engineering estimate, not a binding specification. Motor starting current, harmonics, altitude, and temperature can change the result.
Send this configuration
The load, runtime, phase and estimated battery are prefilled. Add your site country and contact details; the engineering team will confirm the model and the battery bank.
A 15 kW IT load, 60 minutes, three-phase.
The calculator divides 15 kW by 0.9, adds 25%, and returns 20.8 kVA. The nearest standard size is 30 kVA. At a 384 VDC bus, 60 minutes, 0.85 efficiency, and 0.6 DOD, the estimated bank is about 84 Ah; one string of 32 × 100 Ah blocks covers it with margin.
The model sheet then confirms the charger current, the battery room, and the input breaker. The calculation is the start of the quotation, not the end.
How the estimate is calculated
| Input | Value | Result |
|---|---|---|
| Load | 15 kW | — |
| Power factor | 0.9 | 16.7 kVA |
| Design margin | 25% | 20.8 kVA |
| Standard size | 30 kVA | 27 kW at 0.9 PF |
| Runtime | 60 min | — |
| DC bus | 384 VDC | 32 × 12 V blocks per string |
| Usable DOD | 60% | — |
| Estimated capacity | — | 84 Ah |
Standard capacity quick reference.
Typical capacity reference
| UPS size | Real power at 0.9 PF | Typical load |
|---|---|---|
| 1 kVA | 0.9 kW | Small server, POS, router |
| 3 kVA | 2.7 kW | Branch IT, CCTV, clinic desk |
| 5 kVA | 4.5 kW | Small server room, 32 cameras |
| 10 kVA | 9 kW | Server room, 6–8 racks |
| 20 kVA | 18 kW | Small data center, production cell |
| 60 kVA | 54 kW | Plant control, telecom core |
| 100 kVA | 90 kW | Hospital, commercial building |
| 200 kVA | 180 kW | Large data center, process plant |
How to read the result.
Project-specific answers. If your question is not here, send the load list and the site conditions.
Talk to an engineer Why does the calculator add a 25% design margin?
A UPS should not run at 100% load. The margin covers load growth, battery aging, harmonic current, and the difference between nameplate and actual draw. A 20–25% margin is a common design target; 30% is better for a motor-heavy load.
Why is the recommended UPS larger than my kW?
The UPS is rated in kVA, not kW. At a 0.9 output power factor, a 10 kVA UPS delivers 9 kW. The calculator divides kW by the load power factor and then adds the design margin, so the kVA rating is always larger than the kW figure.
How accurate is the battery estimate?
It is a first-pass estimate based on a 0.85 inverter efficiency and 0.6 usable depth of discharge. The actual runtime depends on the battery discharge curve, temperature, end voltage, and charger. Use the model datasheet for the final bank.
Can I use the result for a tender?
Use it to define the capacity range and the battery target, then request a model-specific configuration for the tender. The final submission should include the datasheet, the single-line diagram, and the battery discharge basis.
Does the calculator work for three-phase loads?
Yes, the capacity calculation is the same in kW. The output shows a single standard size; for three-phase projects, confirm the phase configuration and the input current with the model sheet.
What if my load has a large motor?
Do not rely on the continuous kW alone. A direct-on-line motor can draw 5–7 times rated current. Share the motor nameplate and starting method; the UPS may need a higher overload rating or the motor may need a soft starter.