How to Calculate UPS Load and Select the Right UPS Size

How to Calculate UPS Load and Select the Right UPS Size

Key Factors That Influence UPS Sizing

• Total load of all equipment that the UPS needs to protect
  
• Future system expansion allowance
  
• Required battery backup time (runtime)
  
• Redundancy requirements

Identifying Critical vs. Non-Critical Loads
Start by listing all the equipment to be protected by the UPS and categorize them into:

• Critical Loads Must remain powered during outages
  
• Non-Critical Loads Can be powered off during an outage

1.1) How to Calculate the Power Load for UPS Sizing

• Make a list of all electrical devices to be connected to the UPS (e.g., computers, monitors, routers)
  
• Read the device nameplate for power ratings: Voltage (V), Current (A), or Watt (W)
  
• Use the following formulas:
  
  • If Voltage and Current are provided: VA = V × A
    
  • If Watt is provided: VA = W × 1.4 (conversion factor for most electronics)
    
• Add the VA values of all devices
  
• Select a UPS with a higher VA rating than the total load for safety and scalability

1.2) Example Calculation

Devices to be connected:

1. Computer: 220 V, 1 A 220 VA
2. Monitor: 50 W 50 × 1.4 = 70 VA
   
3. Wi-Fi Router: 20 W 20 × 1.4 = 28 VA

Total Load = 220 + 70 + 28 = 318 VA
Choose a UPS rated for at least 400 VA for buffer and future expansion

Conclusion:
For this example, a UPS of 400 VA or more is recommended.

2. Total Power Range and Peak Load Consideration

Calculate the total required power capacity during peak usage (not idle periods). Key parameters to gather:

• Voltage
• Frequency
• Number of phases
• Load current
• Power factor
• Power consumption

Convert all loads to VA (or kVA) using:
 VA = Watts / Power Factor

After summing the total VA, multiply by 1.2 or 1.25 to provide headroom for future expansion.

• Note: Avoid sizing the UPS to run at 100% load for system stability and reliability.
  
  

3. Potentially Problematic Loads
Some devices draw high inrush current or heavy running current:

• Laser printers
  
• Blade servers
  
• Air conditioners
  
• Certain lighting systems
  
• Motors and compressors

These can cause the UPS to overload, issue alarms, or switch to bypass mode.

Solutions:

• Remove such devices from UPS protection if they can safely power off during outages
• Choose a larger UPS, sized at 3 times the VA rating of the problematic load
  

4. Battery Runtime (Backup Duration)
Battery runtime is the duration the UPS can supply power during an outage.

• Select battery capacity based on use case.
  • Some systems only need a few minutes for backup until a generator kicks in
    
  • Others may need longer runtime for controlled shutdowns or extended operation

Summary
Proper UPS sizing requires understanding real-world loads, inrush behavior, runtime needs, and room for growth.
When in doubt, the safest choice is to request a site survey and load analysis by experts.

At BT Connect, we offer:

• On-site UPS load assessment
• Professional guidance for model and capacity selection
• Pre-sales support at no cost

Let BT Connect help you make UPS selection easy, accurate, and stress-free.