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Calcimator

UPS Battery Sizing Calculator

Size an uninterruptible power supply for your home office. Calculate VA rating, battery capacity, and runtime for your equipment.

Inputs

W
W
W
W
min

Results

Minimum VA Rating

650 VA

Total Load390 W
Recommended UPS Size900 VA
Battery Capacity Needed109 Wh
Estimated Actual Runtime11.2 min
Estimated Cost$90.00
How to Use This Calculator
  1. Enter the wattage of each device: Computer Watts, Monitor Watts, Router Watts, and Other Watts for your workstation.
  2. Set Desired Runtime (minutes) — typically 10–30 minutes for graceful shutdown or longer for extended outages.
  3. Review Total Load (W) to ensure it does not exceed the UPS's rated wattage capacity.
  4. Check Required VA and Recommended VA — UPS units are rated in VA; always size up to the next standard model.
  5. Review Battery Wh and Estimated Runtime to verify the UPS will actually run your equipment for the target duration.
  6. Use Estimated Cost to compare UPS brands at the recommended VA rating and select the right capacity.

How the result changes with Computer Power

Computer PowerMinimum VA Rating
150400 VA
5251,025 VA
9751,775 VA
1,3502,400 VA

What each input means

Computer Power
Desktop or laptop power consumption. Desktop: 200-500W, Laptop: 45-100W.
Monitor Power
Monitor power draw. 24" LED: ~25-40W, 32" 4K: ~40-80W.
Router / Modem Power
Combined power for router, modem, and network switch.
Other Equipment
External drives, desk lamp, phone charger, speakers, etc.
Desired Runtime
Minutes of battery backup needed to save work and safely shut down.

What each result means

Total Load
Combined wattage of all connected equipment.
Minimum VA Rating
Minimum UPS VA rating based on total load and 0.6 power factor.
Recommended UPS Size
Nearest standard UPS size with 25% headroom for safety.
Battery Capacity Needed
Watt-hours of battery needed for your desired runtime at 90% inverter efficiency.
Estimated Actual Runtime
Approximate runtime with the recommended UPS size and typical battery capacity.
Estimated Cost
Approximate cost for a consumer UPS at the recommended VA rating.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Computer Power = 300, Monitor Power = 40, Router / Modem Power = 20, Other Equipment = 30 = 5 input(s) provided
  2. Calculate Minimum VA Rating
    Minimum VA Rating
    650 = 650
  3. Calculate Total Load
    Total Load
    390 = 390
  4. Calculate Recommended UPS Size
    900 = 900

Engine last updated . Checked against 2 independently-derived tests — how we verify calculators.

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