UPS Battery Sizing Calculator

Calculate the battery capacity needed for an uninterruptible power supply to support a load for a specified runtime.

Save
W
min
V
%
%

80% for lead-acid, 90% for Li-ion

Required Battery Capacity

28.9 Ah

Battery Energy1.39 kWh
Discharge Current46.3 A
Actual Battery Draw2,222 W

Required Battery Capacity vs Desired Runtime

View formula & how it works →

UPS Battery Sizing

Proper battery sizing ensures the UPS provides the required runtime at the expected load.

Formula

Capacity (Ah) = (Load / Efficiency) x Runtime (hours) / Battery Voltage / DOD

Where DOD is the maximum depth of discharge (80% for lead-acid to extend life, 90% for lithium).

Sizing Considerations

  • Battery capacity degrades over time (plan for end-of-life capacity)
  • Temperature affects capacity (reduce by 1% per degree C below 25 C)
  • Higher discharge rates reduce effective capacity (Peukert effect for lead-acid)

    • Example Calculation

    2000 W load, 30 min runtime, 48 V battery, 90% inverter efficiency, 80% DOD.

    1. 01Runtime in hours: 30 / 60 = 0.5 hours
    2. 02Actual draw: 2000 / 0.90 = 2222 W
    3. 03Capacity: 2222 x 0.5 / 48 / 0.80 = 28.9 Ah
    4. 04Energy: 2222 x 0.5 / 0.80 / 1000 = 1.39 kWh
    5. 05Discharge current: 2222 / 48 = 46.3 A

    Frequently Asked Questions

    Learn More

    Ohm's Law Guide

    A complete guide to Ohm's Law. Learn the relationship between voltage, current, and resistance, with practical examples, the power triangle, and circuit analysis tips.

    Related Calculators

    Surge Protection Calculator

    Size surge protection.

    Three-Phase Power Calculator

    Calculate 3-phase power.

    Cable Ampacity Calculator

    Size power cables.