How to Calculate UPS Load and Runtime | Unified Power (2024)

When it comes to selecting an uninterruptible power (UPS) system, there are several factors to consider. Beyond determining the desired topology and whether you require a single-phase or three-phase unit, it is essential to properly calculate the size of the UPS you need. To do so, you must take into account the intended total load (the combined voltage and amperage of all connected devices), the capacity (the unit’s maximum power output), and the amount of backup time desired from the UPS batteries (how long the UPS can support the equipment during a power outage).

Although most major UPS manufacturers provide helpful product selectors and runtime calculators, read on to learn how to size your UPS load and factor runtime the old-fashioned way.

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Factors to Consider When Calculating UPS Load and Runtime

Because UPS products have different specifications, it is critical to carefully consider a variety of aspects when selecting the optimal model to meet your needs. The three most important factors to take into account are the UPS’s rating, the load it will support and the amount of runtime desired.

UPS Rating

UPS systems are typically rated in either kilowatts (kW), volts amps (VA), or kilo-volt-amperes (kVA). While VA or kVA power rating represents the power limitation accepted by the UPS, the Watts rating is the power output of the UPS and determines the unit’s ‘real power.’

In a direct current (DC) circuit, watts = volts x amps (in other words, 1 kW = 1 kVA). However, when the uninterrupted power supply system uses AC (alternating current) ── as most data centers and other buildings do ── it reduces the available power (watts) in apparent power (volt-amperes). The ratio of these two numbers is called the power factor. The power factor of an AC power system is defined as the ratio of the real power absorbed by the load to the apparent power flowing in the circuit and is calculated as: watts = volts x amps x power factor. Power factors differ depending on the UPS. For example, a 100 kVA UPS system with a power factor of 0.8 can only support 80 kW of real power.

Power Load

The UPS load is the combined amount of power that attached electrical devices will consume. To calculate the load, you add the total watts of each piece of equipment that will be connected to the UPS. For example, if you want the UPS to support a 120W PC, a 30W VPN router, a 960W server, a 280W network switch and a 480W storage device, the total load required is 1870 W.

Battery Capacity

While the load represents the total equipment the UPS will be tasked with protecting, you also must determine how much time you want that load to stay up and running during a power outage. This will establish the UPS runtime. Every UPS has an internal battery that will supply a limited amount of power if the utility supply isn’t available. However, many UPS models can incorporate additional battery modules to increase runtime by minutes or hours. The battery capacity is measured in AH or Amp-hrs.

How to Calculate UPS Load and Run Time

Many UPS manufacturers offer online UPS calculators and sizing tools that make it easier to match a backup power supply to your needs. However, if you don’t have immediate access to a UPS selector, you can calculate the load by gathering measurements and completing a series of simple steps. It is important to note that while adding more batteries to a UPS can increase the battery runtime to support the load, it does not increase the capacity of the UPS. You must first ensure that the UPS is adequately sized for your load, and then add batteries to accommodate your runtime needs.

To size the UPS:

1. List all the equipment and devices you want the UPS to protect.

2. List the amps and volts for each device. These ratings can typically be found on the label on the back

of the equipment.

3. Multiply amps by volts to determine VoltAmps (VA). Some devices may list their power requirements in watts. To convert watts to VA, divide the watts by power factor.

4. Multiply the VA by the number of pieces of equipment to get the VA subtotals.

5. Add the VA subtotals together to get the total power requirement.

6. Multiply the total by 1.2 to get the grand total. This step accounts for future expansion.

When choosing a UPS, be sure that the VA requirement of supported equipment does not exceed the VA rating of the UPS.

To determine the backup time:

1. Multiply the battery rating (in Ah) × the battery rating (in V) × the number of batteries × the battery efficiency.

2. Then divide that number by the load in Watts (W).

While runtime may seem like a simple thing to quantify, understanding the facts behind the numbers helps determine the optimal battery backup solution for your particular business or application.

Consider the following solution scenarios:

1. UPS with 10-15 minutes of runtime and no generator ── This solution allows time to safely shut down connected equipment and save work-in-progress.

2. UPS with 10-15 minutes of runtime and a generator ── This solution will keep connected systems up and running until the generator powers on.

3. UPS with two or more hours of battery runtime ── In some cases, generators may not be practical and organizations that wish to remain up and running during an extended outage must rely solely on UPS batteries.

Rely on the Experts: UPS Services with Unified Power

Regardless of the size of your UPS solution, Unified Power is uniquely qualified to help ensure it remains in optimal condition and ready to perform when you need it most. With a nationwide staff of professional service engineers, we provide a wide range of UPS and generator maintenance plans, replacement battery services, extended warranties, UPS rentals, site surveys, and other critical power services. Our team can also help you cross-reference the ideal power protection solution to meet your needs. Contact us today for more information.

How to Calculate UPS Load and Runtime | Unified Power (2024)


How to Calculate UPS Load and Runtime | Unified Power? ›

UPS runtime is the amount of time a UPS can supply battery power to the connected load. You can calculate runtime yourself by multiplying UPS battery capacity by UPS input voltage and then dividing the sum by the total supported load (in watts.)

How is UPS load capacity calculated? ›

To calculate the load, you add the total watts of each piece of equipment that will be connected to the UPS. For example, if you want the UPS to support a 120W PC, a 30W VPN router, a 960W server, a 280W network switch and a 480W storage device, the total load required is 1870 W.

How to calculate power consumption for UPS? ›

To calculate the total load or power requirements for a UPS (Uninterruptible Power Supply), follow these steps: List the Connected Devices, Determine Power Ratings (Power (Watts) = Voltage (Volts) × Current (Amps)), Calculate Individual Power Consumption, Factor in Future Expansion, Apply a Safety Margin (20% to 30%), ...

How long will a 1500VA UPS last? ›

1500VA is the maximum output (voltage x current) of the unit. At 1500VA the backup would last 216 VA/H/1550VA = . 144 HR or 8 Minutes.

How do you calculate watts from UPS load? ›

Because of this, most UPS manufacturers will list a “power factor” to use and calculate the maximum wattage a UPS system can handle. This means that the formula for watts = volts x amps x power factor. For example, 1kVA UPS from N1C has the capacity to power 900 watts of connected equipment.

How do you calculate UPS runtime? ›

UPS runtime is the amount of time a UPS can supply battery power to the connected load. You can calculate runtime yourself by multiplying UPS battery capacity by UPS input voltage and then dividing the sum by the total supported load (in watts.)

How do you calculate loading capacity? ›

To calculate the capacity load ratio you must divide the required hours on a project by the amount of time available to complete it and multiply it by 100. For instance, if a project designer requires 80 hours to complete a project but they only have 60 hours available, they are at 133% — meaning they are overloaded.

How do I calculate my UPS kW? ›

UPS systems are rated either in kilowatts (kW) or in kilo-volt-amperes (kVA). They can be regarded as the same in number. For example, in a direct current (DC) circuit, watts = volts x amps. In other words, 1 kW = 1 kVA.

What is the runtime for 1000VA UPS? ›

What is the typical runtime at full load of a 1000VA UPS system? From 4 minutes to 30 minutes on internal UPS batteries, depending on the UPS. Extra UPS battery packs can be added to increase this.

How do you calculate power load? ›

Some appliances might state The power rating in amps (A) and volts (V). You can use the load calculation formula, Power (W) = Voltage (V) × Current (A). It will convert the information to watts. Determining Load Types: Electrical loads can differ based on their characteristics.

How do I calculate what size UPS I need? ›

Determine the total load for the UPS in watts by adding up the watts used by all of the connected devices. Multiply the battery capacity by the input voltage, then divide that number by the total load.

How long will a 3000 VA UPS last? ›

Therefore, with a load of 500W, the 3kVA will last for 1.14048 hours ( approximately 68.4 minutes ). This about 52% more time than that of the 2kVA Online UPS.

How long will a 1000 VA UPS last? ›

For example, if you've got a 1,000-watt UPS with 125-minutes of standby time, your backup should last for 8-hours with no power outage.

How to calculate power backup calculation for UPS? ›

If the capacity is given in amp-hours and current in amps, time will be in hours (charging or discharging). How do you calculate battery backup hours? Backup time of UPS (in hours) = [ Battery rating (in Ah) × Battery rating (in V) × Number of Batteries × Battery Efficiency ] / Load in Watts (W).

How much power does my UPS use? ›

The average smaller UPS system will start from 12-Volt batteries and upwards. In this case it would require approximately 1.2 kW to fully charge, costing around $0.36 AUD (36 cents). Following that, it will take roughly 3 to 6 watts per hour to maintain that full charge.

What is UPS load capacity? ›

Capacity is how much power a UPS system can provide (measured in Watts). The higher the capacity, the more electronic equipment, and devices it can support. To find the UPS capacity, you will need to calculate the load. The Load is the combined amount of power each of the devices use.

How is load limit calculated? ›

Working Load Limit (WLL) is the maximum working load designed by the manufacturer. This load represents a force that is much less than that required to make the lifting equipment fail or yield. The WLL is calculated by dividing the breaking load limit (BLL) by a safety factor (SF).

How much load can an UPS take? ›

Estimate the Required UPS Capacity

That is to say, one only runs the uninterruptible power supply system around 80% of the capacity to support the load calculated. For example, if the total required capacity/load is 200 W, it is better to choose an UPS with a capacity of 250 W (250 W x 0.8 = 200 W) or so.

How is UPS weight calculated? ›

The formula for calculating a parcel's dimensional weight involves multiplying the package's length, width, and height, and then dividing the product by the carrier's dimensional factor (DIM factor)—which is 139 (for FedEx and UPS Daily Rates) or 166 (for USPS and UPS Retail Rates).

What is the maximum capacity of UPS? ›

A 10KVA output is generally the largest single Phase UPS system available. This is due to the output amperage and cable requirements. 10KVA=10,000VA / 230Vac = 43.5Amps.

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