VA to Watts Calculator

How to Convert VA to Watts

In electrical engineering, understanding the difference between Apparent Power (VA) and Real Power (Watts) is crucial for sizing equipment like generators, UPS systems, and transformers.

The key factor connecting these two is the Power Factor (PF), which represents the efficiency of the power usage.

Calculation Formulas

Understanding Power Factor

Power Factor is a ratio between 0 and 1 (or 0% to 100%) that indicates how effectively electricity is being converted into useful work.

• 1.0 (Unity): 100% efficiency. Occurs in purely resistive loads like electric heaters and incandescent light bulbs. In this case, VA = Watts.
• 0.8 (Lagging): The industry standard estimate for mixed loads, including computers, motors, and servers. Most UPS systems are rated with a 0.8 PF.
• 0.6 - 0.7: Common for inductive loads like older electric motors or fluorescent lighting ballasts.

Real World Examples

Example 1: Sizing a UPS

You have a computer server that consumes 500 Watts. You want to buy a UPS. If the UPS has a power factor of 0.6, what VA rating do you need?

VA = Watts / PF
VA = 500 / 0.6 = 833.33 VA
You would need a 1000VA UPS to be safe.

Example 2: Generator Capacity

A generator is rated at 5 kVA (5000 VA). If you are running equipment with a power factor of 0.8, how many Watts can it support?

Watts = VA × PF
Watts = 5000 × 0.8 = 4000 Watts

Why is VA always higher than Watts?

Unless you have a purely resistive load (Power Factor = 1), Apparent Power (VA) will always be higher than Real Power (Watts). This is because some current is used to create magnetic fields (reactive power) in motors and transformers, which doesn't perform "real" work but still loads the wires and source.