UPS VA -vs- Watts

Watts vs VA is one of the most confusing topics when buying a UPS (Uninterruptible Power Supply). Many people assume the VA number is all that matters—until their UPS overloads or shuts down unexpectedly.

In this guide, Nerd Base One explains the difference between UPS watts vs VA, how power factor affects capacity, and how to choose the right UPS size for your PC, gaming setup, server, or home office.

What Is the Difference Between Watts and VA in a UPS?

UPS Wattage (W): Real Power Output

Watts (W) represent the real usable power your devices consume.

This is the most important number when selecting a UPS because it determines:

• Whether your PC or server can run at all

• How much equipment the UPS can support safely

• If the UPS will overload during power loss

Common devices that draw watts:

• Desktop PCs and gaming rigs

• Monitors and TVs

• Routers, modems, and switches

• NAS and small servers

If your load exceeds the UPS’s watt rating, the UPS will fail instantly.

UPS VA (Volt-Amps): Apparent Power

VA (Volt-Amps) measures apparent power, which includes:

• Real power (watts)

• Reactive power caused by inefficiencies

UPS manufacturers list VA because it represents the electrical capacity and stress on the UPS hardware.

For most electronics, VA is always higher than watts.

Power Factor Explained (Why VA ≠ Watts)

The relationship between watts and VA is defined by power factor (PF):

Typical power factor values:

• Modern PCs, monitors, and consoles: 0.6 – 0.9

• Most consumer UPS units assume: 0.6 – 0.7

UPS Power Factor Examples

• 1000 VA UPS × 0.6 PF = 600 W

• 1500 VA UPS × 0.67 PF ≈ 1000 W

This is why UPS listings often look like:

1500 VA / 900 W UPS

Should You Choose a UPS by Watts or VA?

Always Size a UPS by Watts First

When choosing a UPS:

1. Watts determine compatibility

2. VA only needs to be high enough to support that wattage

Searching for “UPS sizing calculator” or “how many watts does my UPS need” usually leads back to this same rule.

How to Calculate the Right UPS Size (Step-by-Step)

Step 1: Calculate Total Power Draw in Watts

Check power ratings for:

• PC power supply

• Monitor(s)

• Router and modem

• External drives or peripherals

Example PC setup:

• Gaming PC: 500 W

• Monitor: 50 W

• Router + modem: 20 W

Total load: ~570 W

Step 2: Add UPS Headroom (Very Important)

Add 25–30% extra capacity for:

• Startup surges

• Power supply inefficiency

• Future upgrades

Step 3: Choose a UPS That Supports That Load

You should look for:

• At least 750 W output

• Typically 1200–1500 VA

A 1500 VA / 900–1000 W UPS is ideal for this setup.

Why VA Rating Still Matters in a UPS

Even if the watt rating looks sufficient, a low VA rating can cause:

• UPS overload warnings

• Shorter battery runtime

• Excess heat and reduced lifespan

UPS VA Rule of Thumb

UPS Wattage and VA Cheat Sheet

Actual usable power depends on UPS power factor and efficiency.

How Long Will a UPS Run a PC?

A common search question is “How long will a UPS run my PC?”

A standard UPS is designed to:

• Save your work

• Shut down safely

• Handle short power outages

It is not meant for hours of runtime.

For longer backup time, you’ll need:

• A higher-capacity UPS

• External battery expansion packs

• Or a dedicated battery power system

Final Thoughts: Choosing the Best UPS

When choosing the best UPS for your PC, gaming rig, or server:

• Size by watts first

• Ensure VA is high enough

• Add at least 30% headroom

• Understand power factor limitations

Mastering UPS watts vs VA ensures your equipment stays protected and your money isn’t wasted.

Stay powered. Stay nerdy.
Nerd Base One