UPS power
72 kW
UPS Sizing & Battery Runtime Calculator
Size an uninterruptible power supply and its battery bank from the load, power factor and required autonomy — and see the actual runtime the installed battery delivers.
Result
Enter your load → get a full design & BOM in seconds
Sample outputRecommended UPS rating
80 kVA
50 kW load · PF 0.8 · 30 min autonomy · VRLA lead-acid (12 V block)
Battery bank
32 blocks · 200 Ah
Actual runtime
39 min
Load margin
15%
Sizing calculation
| Step | Value |
|---|---|
| Load apparent power | S = P ÷ PF = 50 kW ÷ 0.8 = 62.5 kVA |
| Required UPS (loading factor) | 62.5 ÷ 0.8 = 78.1 kVA → standard 80 kVA |
| Battery energy | E = P·t ÷ (ηinv·ηbat·DOD) = 50 kW × 0.50 h ÷ (0.94 × 0.9 × 0.5) = 59.10 kWh |
| Total battery capacity | 59.10 kWh ÷ 384 V = 154 Ah |
| Series blocks per string | 384 V ÷ 12 V = 32 |
| Parallel strings | 154 Ah ÷ 200 Ah = 1 |
Battery configuration
| String voltage | 32 × 12 V = 384 V |
| Installed capacity | 1 × 200 Ah = 200 Ah |
| Actual runtime | (200 Ah × 384 V × 0.94 × 0.9 × 0.5) ÷ 50 kW = 39 min |
| Estimated recharge | 200 Ah ÷ 20 A (0.1C) × 1.1 ≈ 11.0 h |
Bill of materials
| Equipment | Spec | Qty | Subtotal |
|---|---|---|---|
| Online double-conversion UPS | 80 kVA / 72 kW · 384 V DC bus | 1 | POA |
| VRLA lead-acid (12 V block) battery bank | 32S×1P (32 blocks, 200 Ah @ 384 V) | 1 | POA |
| Battery charger / rectifier | 20 A charging current | 1 | POA |
| Total equipment (UPS + charger) | POA |
For facility managers, data-center designers and electrical engineers sizing single- or three-phase UPS systems with VRLA or LiFePO₄ battery banks.
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Worked example
A pre-computed reference example (crawlable — no JavaScript required). Enter your own parameters above for a live result.
Example 1 — 50 kW data-center load, 30 minutes autonomy
Recommended UPS rating
80 kVA
50 kW load · PF 0.8 · 30 min autonomy · VRLA lead-acid (12 V block)
UPS power
72 kW
Battery bank
32 blocks · 200 Ah
Actual runtime
39 min
Load margin
15%
Sizing calculation
| Step | Value |
|---|---|
| Load apparent power | S = P ÷ PF = 50 kW ÷ 0.8 = 62.5 kVA |
| Required UPS (loading factor) | 62.5 ÷ 0.8 = 78.1 kVA → standard 80 kVA |
| Battery energy | E = P·t ÷ (ηinv·ηbat·DOD) = 50 kW × 0.50 h ÷ (0.94 × 0.9 × 0.5) = 59.10 kWh |
| Total battery capacity | 59.10 kWh ÷ 384 V = 154 Ah |
| Series blocks per string | 384 V ÷ 12 V = 32 |
| Parallel strings | 154 Ah ÷ 200 Ah = 1 |
Battery configuration
| String voltage | 32 × 12 V = 384 V |
| Installed capacity | 1 × 200 Ah = 200 Ah |
| Actual runtime | (200 Ah × 384 V × 0.94 × 0.9 × 0.5) ÷ 50 kW = 39 min |
| Estimated recharge | 200 Ah ÷ 20 A (0.1C) × 1.1 ≈ 11.0 h |
Bill of materials
| Equipment | Spec | Qty | Subtotal |
|---|---|---|---|
| Online double-conversion UPS | 80 kVA / 72 kW · 384 V DC bus | 1 | POA |
| VRLA lead-acid (12 V block) battery bank | 32S×1P (32 blocks, 200 Ah @ 384 V) | 1 | POA |
| Battery charger / rectifier | 20 A charging current | 1 | POA |
| Total equipment (UPS + charger) | POA |
Example 2 — 120 kW load, 60 minutes, lithium battery
Recommended UPS rating
200 kVA
120 kW load · PF 0.9 · 60 min autonomy · LiFePO₄ lithium (48 V module)
UPS power
180 kW
Battery bank
10 blocks · 350 Ah
Actual runtime
68 min
Load margin
35%
Sizing calculation
| Step | Value |
|---|---|
| Load apparent power | S = P ÷ PF = 120 kW ÷ 0.9 = 133.3 kVA |
| Required UPS (loading factor) | 133.3 ÷ 0.8 = 166.7 kVA → standard 200 kVA |
| Battery energy | E = P·t ÷ (ηinv·ηbat·DOD) = 120 kW × 1.00 h ÷ (0.94 × 0.95 × 0.9) = 149.31 kWh |
| Total battery capacity | 149.31 kWh ÷ 480 V = 311 Ah |
| Series blocks per string | 480 V ÷ 48 V = 10 |
| Parallel strings | 311 Ah ÷ 350 Ah = 1 |
Battery configuration
| String voltage | 10 × 48 V = 480 V |
| Installed capacity | 1 × 350 Ah = 350 Ah |
| Actual runtime | (350 Ah × 480 V × 0.94 × 0.95 × 0.9) ÷ 120 kW = 68 min |
| Estimated recharge | 350 Ah ÷ 35 A (0.1C) × 1.1 ≈ 11.0 h |
Bill of materials
| Equipment | Spec | Qty | Subtotal |
|---|---|---|---|
| Online double-conversion UPS | 200 kVA / 180 kW · 480 V DC bus | 1 | POA |
| LiFePO₄ lithium (48 V module) battery bank | 10S×1P (10 blocks, 350 Ah @ 480 V) | 1 | POA |
| Battery charger / rectifier | 35 A charging current | 1 | POA |
| Total equipment (UPS + charger) | POA |
How it was calculated
- · Load apparent power: S = P ÷ PF.
- · Required UPS rating: S_UPS = S ÷ loading factor (typical 0.8), rounded up to a standard size.
- · Battery energy: E = P · t ÷ (η_inv · η_bat · DOD).
- · Battery capacity: Ah = E ÷ V_dc; series blocks = V_dc ÷ V_block; parallel strings = required Ah ÷ block Ah.
- · Actual runtime: t = (installed Ah · V_dc · η_inv · η_bat · DOD) ÷ P.
Referenced standards
| Standard | Scope |
|---|---|
| IEC 62040-3 | Uninterruptible power systems — method of specifying performance and test requirements |
| IEEE 1184 | Guide for batteries for uninterruptible power supply systems |
| IEEE 485 | Recommended practice for sizing lead-acid batteries for stationary applications |
Frequently asked questions
How do I size a UPS for my load?
UPS kVA = load kW / Power Factor, plus 20-30% margin and future growth. A 40 kW IT load at 0.9 pf needs ~44 kVA, so select 60 kVA. Add margin for inrush and non-linear loads. The calculator sizes UPS kVA, battery Ah and runtime.
How is UPS battery runtime calculated?
Runtime depends on battery capacity (Ah), string voltage, load and efficiency. For a 40 kW load on a 240 V battery string, a 100 Ah bank gives roughly 20-30 minutes. The calculator computes actual runtime from battery blocks, DoD and load, and reports recharge time.
What is the difference between online and line-interactive UPS?
Online (double-conversion) UPS continuously rectifies and inverts, giving zero transfer time and full power conditioning — required for data centers. Line-interactive passes utility power and corrects only on events, cheaper but with a brief transfer. The calculator's sizing assumes online double-conversion for critical loads.
What battery type is used in UPS systems?
Valve-regulated lead-acid (VRLA) dominates UPS for low cost and maintenance-free operation, with a 3-5 year typical life. Lithium (LFP) is gaining share for longer life (10+ years), smaller footprint and higher cycle count, at 2-3x the upfront cost. The calculator sizes the battery bank for either chemistry.
How much runtime do I need before the generator starts?
Battery runtime must bridge to generator start, typically 5-15 minutes (generators reach full load in 30-60 s). Without a generator, size for 30-60 minutes for graceful shutdown. Longer runtime adds cost roughly linearly. The calculator lets you set runtime and sizes the battery accordingly.
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Results are engineering estimates for preliminary design and reference only. Always verify with the applicable standards, the equipment nameplate and a licensed engineer before procurement or installation.
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