What is the UPS Runtime Calculator?
Estimate backup runtime from nominal battery energy and a constant connected load.
This simplified energy model cannot reproduce a manufacturer discharge curve at every load.
How to use the UPS Runtime Calculator
Start with measurements from the same device, connection, file, or scenario whenever possible. Enter Battery voltage, Battery capacity, Battery count, UPS efficiency, Usable battery depth, Connected load using the units printed beside each field. Avoid mixing bits with bytes, decimal storage units with binary units, or peak specifications with typical operating values.
- Collect the requested values and confirm their units before entering them.
- Choose realistic efficiency, overhead, compression, reserve, or usage assumptions where those options are provided.
- Select Calculate UPS Runtime, then review the primary answer, all four color-coded detail cards, the caution note, and the five calculation steps.
For planning decisions, repeat the calculation with a lower, expected, and higher assumption. A range usually communicates uncertainty better than one apparently precise number.
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For optional supporting equipment or reference material, you can browse Battery reference books (paid link) on Amazon.com. Review capacity units, load assumptions and manufacturer documentation. Do not modify, assemble or charge batteries outside their approved instructions. No purchase is required to use this calculator.
How to understand the result
This simplified energy model cannot reproduce a manufacturer discharge curve at every load.
The large highlighted value is the main estimate. The cyan, purple, green, and orange cards provide supporting quantities such as converted units, intermediate totals, rates, physical dimensions, capacity, or time. These details make it easier to check whether the result is reasonable.
Battery and backup-power estimates use rated capacity and an average load. Battery chemistry, voltage behavior, temperature, age, discharge rate, conversion losses, protection cutoffs, charging negotiation, and manufacturer controls can materially change real runtime or charging time.
Example and practical interpretation
For example, two 12 V, 9 Ah batteries at 85% inverter efficiency and 70% usable depth supporting a 300 W load produce about 25 minutes 42 seconds. Manufacturer runtime charts remain preferable for final equipment selection.
The five-step explanation beneath the result uses the exact values entered during the current calculation. It shows the conversion or setup, the formula, intermediate arithmetic, final operation, and displayed rounding rather than presenting a generic formula alone.
Formula and calculation method
The calculation runs locally in your browser and uses only the values entered on this page.
Important limitations
Technology estimates simplify real systems. Hardware, software, network conditions, measurement conventions and manufacturer behavior can change actual results.
UPS Runtime Calculator FAQs
Sources and methodology
Official source links support terminology and measurement context. The arithmetic runs locally in your browser.