Get Expert Power Protection with the Right UPS Sizing

To succeed in today's digital world, it is imperative to ensure that your operations are running smoothly. That's why a reliable UPS (uninterruptible power supply) system is essential - it provides critical backup power to safeguard your equipment and prevent data loss during power outages. Whether you’re protecting your valuable electronics at home or ensuring the smooth operation of critical systems in the office, choosing the right UPS and appropriate sizing is crucial.

Once the need for an Uninterruptible Power Supply (UPS system) has been established, there are a number of considerations that should be addressed to ensure its successful installation. One of which is identifying the information needed to correctly size a UPS for the required load. Overlooking this could result in an undersized UPS that cannot adequately cope with the load demand or overspending on a UPS that is too big with too high a kVA rating.

So, whether you're an engineer tasked with specifying a UPS system or a business owner looking to safeguard your operations, this guide aims to simplify the process of sizing a UPS by taking into account various factors that influence its performance and efficiency. We will discuss the factors you need to consider before choosing the ideal UPS system for your needs. We will also cover common mistakes people make when sizing a UPS system and tips for getting the most out of it.

With the help of this guide, you’ll be equipped to make an informed decision and find the perfect UPS to suit your needs. So, let’s dive in, and make sizing a UPS a breeze.

What is the importance of UPS sizing?

Correctly sizing your UPS (uninterruptible power supply) system is important because it determines the effectiveness and reliability of the backup power provided during a power outage. By properly sizing your UPS, you can ensure that it will be able to support the necessary load and provide uninterrupted power for the required duration.

In addition, to maximise the performance and efficiency of your power protection system, getting the size of your uninterruptible power supply (UPS) system right is critical. This is because an oversized UPS system will cost you more money upfront, while a too-small system will not provide adequate runtime or backup power for connected devices.

Before you begin sizing your UPS system, you must consider the right:

  • Battery backup time,
  • Load characteristics,
  • And, overload protection needed.

To properly size a UPS for any application:

  • The equipment to be protected must be listed with the current amps/A and voltage/V, with the power rating converted to Volt Amps (VA)
  • The UPS capacity rating must be greater than the total power needed for the protected equipment by 15% to ensure sufficient protection and account for growth.

Factors to consider when sizing a UPS:

  • Determining the acceptable delay between loss of primary power and availability of UPS power is a critical factor to consider when sizing a UPS. This delay should be sufficient for the devices connected to the UPS to power down and for the battery to discharge, but not so long that it results in system instability. Ideally, the battery on the UPS should have a capacity of at least three-four times the load it is designed to support.
  • The length of time that emergency or backup power is required and the criticality of the load that the UPS must bear are also important factors to consider. In other words, if an uninterruptible power supply is required for a server that is essential for business operations, then it must have an adequate battery capacity to ensure uninterrupted service during power outages.
  • Lastly, it is important to use a UPS with a VA capacity rating that is greater than the total power needed for the protected equipment, by at least 15%. Doing so helps ensure that sufficient power is available during a power failure event.

Correctly sizing a UPS system for a business requires several steps:

  • Identify the critical loads:

The first step is to identify the critical loads that need to be protected by the UPS. These are the systems or devices that are essential for the business to function, such as servers, network equipment, and other critical infrastructure.

  • Determine the power requirements:

Once the critical loads have been identified, the next step is to determine their power requirements. This includes the voltage, current, and power factor for each load. The total power requirement for all critical loads is known as the "apparent power," and it is measured in VA (volt-amperes).

  • Choose the appropriate UPS topology:

There are several different UPS topologies to choose from, including online, line-interactive, and standby. Online UPS systems provide the highest level of protection and are recommended for critical loads. Line-interactive UPS systems are less expensive and are suitable for less critical loads. Standby UPS systems are the least expensive but also provide the least protection.

  • Calculate the required battery capacity:

The required battery capacity is determined by the runtime required and the total power requirement of the critical loads. The formula for calculating the required battery capacity is: Battery Capacity (Ah) = (Runtime (hours) x Total Power Requirement (VA)) / (Battery Voltage x Battery Efficiency)

To size your needs: Total watts of your equipment x their total amperage and add 15% of that total to get your total requirement.

  • Select the appropriate UPS:

Once the required battery capacity has been calculated, the next step is to select a UPS that meets the power requirements and has the appropriate battery capacity. It is important to choose a UPS from a reputable manufacturer and to ensure that it has been tested and certified to the appropriate standards.

  • Consider future expansion:

It's important to consider the possibility of future expansion and to choose a UPS that has the capacity to accommodate any additional loads that may be added in the future.

  • Maintenance:

Proper maintenance is important to ensure the UPS system continues to function properly and to prolong its lifespan. This includes regular testing, battery replacement, and cleaning.

Common mistakes to avoid with UPS sizing:

When it comes to sizing a battery-based uninterruptible power supply (UPS), there are a number of things that you must keep in mind. These include the size of the battery, the load of the UPS, and more importantly, the power demands of the system. It is essential to use an appropriate UPS sizing formula to calculate the right battery capacity required for your system. However, using inadequate sizing calculations can lead to substandard power protection and failure of the battery.

Therefore, it is important to use approved battery components while sizing a UPS to ensure reliable power protection. Besides, it is vital to not overload the UPS with power demands as this can lead to permanent damage to the battery and its components. Lastly, it is crucial to right-size a UPS as power demands change over time to avoid under or over-utilization of the battery that may result in damage or failure of the battery and its components.

10 Tips for getting the most out of your UPS system:

  • Ensure your UPS is appropriately sized for your power load by keeping it right sized as power demands change over time – this guide is designed to assist you with that.
  • Regularly assess your power requirements and adjust your UPS capacity accordingly to ensure optimal performance and efficiency.
  • Take into account any potential power spikes or surges that may occur in your area and select a UPS with adequate surge protection.
  • Invest in a UPS with advanced monitoring and management features, such as remote monitoring and automatic shutdown capabilities, to enhance the reliability and functionality of your power protection system.

Check out our Virtual Service for 24/7 remote monitoring and solutions supported by our approved and highly qualified engineers.

  • Regularly check battery voltage and capacity to ensure the UPS is always ready for critical power needs.
  • Properly maintain your UPS system by conducting regular inspections, cleaning, and battery – this ensures it remains in good health and ensures the longevity and efficiency of the UPS system.

BPC can offer a range of maintenance agreements designed to meet specific customer requirements regardless of quantity, size, make/model etc.

  • When selecting a UPS, consider the device wattage, VA rating, and runtime, as well as the size of the system for which it is intended. Keep in mind that not all devices need the same amount of power protection. Also, keep an eye out for state- and country-specific regulations regarding battery usage and disposal.
  • Consider future expansion plans when sizing your UPS system to avoid the need for frequent upgrades or replacements.
  • Utilising a UPS system can provide backup power during electricity outages, act as a power conditioner, and decrease noisy power sources. However, be sure to consider the cost of running a UPS system versus buying a conventional power supply before deciding on whether or not to use one.
  • Choose highly trained professionals for expert guidance as they can identify issues and potential failures early on, allowing you to avoid or mitigate any downtime or costly repairs.

Here at BPC, we have a team of highly skilled and experienced engineers with advanced industry knowledge that can provide you with technical expertise and guidance from system design, site surveys, UPS health checks, installations and complete commissioning of your system etc. With our services, you can rest assured that your UPS investment is in expert hands, is a worthwhile investment, and is capable of long-term use.


In conclusion, the right UPS system can help you protect your data and system from power fluctuations, voltage spikes, and voltage outages. If you are setting up a server or building a data centre, it is crucial to size your backup power system properly. Depending on the load of your system, you will need to factor in things such as voltage, amperage, and connectivity options. It is also important to check the supported battery backup time of your UPS system depending on how critical your systems are and how long they can run on battery backup during an outage. One of the most common mistakes is underestimating the power requirements for servers and other electronic devices. So, if you want to protect your systems and data from power outages or voltage fluctuations, ensure that you get expert advice with UPS sizing from the beginning of the setup process.

Contact us now to see how we can help you size your UPS correctly and make the most of your UPS power protection investment. Or you can head to our Services page to explore the full range of personalised guidance and solutions support we can offer you.


View this product

Pre-Sales Support

More info
Get Expert Power Protection with the Right UPS Sizing

BPC's Accreditations & Certifications

SafeContractor RISQS ISO 9001:2015 CPD/CIBSE CHAS JOSCAR Constructionline Cyber Essentials