How to size your UPS
Size your UPS in 6 steps. Add up watts, convert to VA, add 25% headroom and check runtime, with a worked example you can copy.
Sizing a UPS follows a clear sizing method. Here is the full process with an example.
Step 1: List your devices
Write down every device you want to protect and its wattage. Use the label, the power adapter, or a plug-in power meter for real numbers.
Step 2: Add the total load
| Device | Watts |
|---|
| Router and modem | 25 |
| Network switch | 30 |
| NAS | 40 |
| Desktop PC | 250 |
| Monitor | 35 |
| Total | 380 |
Step 3: Add a growth margin
Add 20% to 25% for future devices. 380 W x 1.25 = 475 W.
Step 4: Convert to VA
VA = watts / power factor. Most modern UPS units use a power factor of 0.9, and older ones use 0.6. At 0.9, 475 W is about 528VA, so a 750VA unit is the minimum.
Step 5: Check runtime
Open the maker's runtime chart. Runtime vs load is not a straight line. A UPS at 80% load may run only a few minutes, while the same unit at 30% load runs far longer. Battery capacity and load percentage decide the result. If the chart shows too little time, choose the next size up, which in this example would be 1000VA or 1500VA.
Step 6: Pick the type
Line-interactive suits home offices and small networks. Online double-conversion costs more but gives the cleanest power, so it fits servers and sensitive gear. Online vs line-interactive comes down to how much downtime or bad power you can tolerate.
Plan for expansion
If you may add equipment, choose a model that accepts external battery packs. A simple spreadsheet with columns for device, watts, VA, and date added keeps your sizing current, and many makers offer a free sizing calculator.
Comments (0)
No comment