UPS Sizer & Runtime Calculator
Analyze your PC's power load, calculate the exact Volt-Ampere (VA) battery capacity required, and find Pure Sine Wave models tested compatible with Active PFC power supplies.
1. UPS Battery Sizer & Pure Sine Wave Checker
2. UPS Sizing Output
How to Size a UPS for a Modern Desktop PC
An Uninterruptible Power Supply (UPS) is essential for protecting expensive desktop hardware from blackouts, brownouts, and voltage surges. However, sizing a UPS for a desktop system requires understanding two separate parameters: **VA (Volt-Amperes)** and **Watts (W)**.
Watts measure the real electrical power drawn by your components (e.g. CPU, GPU, storage), while VA measures the apparent power which includes circuit impedance. The ratio is the **Power Factor (PF)**. Modern high-quality PC power supplies incorporate Active PFC circuits, achieving a power factor of **0.90–0.98**.
To calculate your minimum UPS rating:Minimum UPS VA = Total Load Watts / 0.90If your gaming PC and monitor draw 540W combined, you need a UPS rated for at least **600W** and **600W / 0.9 = 667VA**. Sizing too close to the limit can cause the UPS to trip its safety overload circuit when a transient power spike occurs, so adding a 20% margin is highly recommended.
Simulated vs. Pure Sine Wave: The Active PFC Catch
Standard grid utility power is delivered as a smooth, continuous AC wave (Pure Sine Wave). Budget battery backups construct a stepped, blocky approximation (Simulated or Modified Sine Wave) when running on battery to save manufacturing costs.
This stepped wave is fine for basic electronics (like router bricks or simple office computers). But if you plug a high-end PSU with **Active Power Factor Correction (Active PFC)** into a simulated sine wave UPS, the PSU's line-filtering stage interprets the stepped voltage steps as a dangerous electrical anomaly. The PSU safety protection (OPP/OVP) triggers, instantly shutting down your PC—defeating the entire purpose of having a battery backup. Always buy a **Pure Sine Wave** UPS (such as CyberPower's PFC series or APC's Smart-UPS series) for gaming or creator workstations.