UPS Runtime Calculator

A UPS (Uninterruptible Power Supply) keeps your devices running during a power outage — and this calculator tells you exactly how long it will last. Enter your UPS Capacity, Battery Capacity, Battery Voltage, and Connected Load, then select your UPS Efficiency and Battery Age to get your Estimated Runtime in minutes and hours. Secondary outputs include Load Percentage and Available Battery Energy in watt-hours.

VA

The VA rating of your UPS system

W

The watt rating of your UPS system

Ah

Amp-hour rating of the UPS battery

W

Total wattage of devices connected to UPS

Battery condition affects runtime

Results

Estimated Runtime

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Runtime (Hours)

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Load Percentage

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Available Battery Energy

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Frequently Asked Questions

How accurate is this UPS runtime calculator?

This calculator provides estimates based on standard battery performance and UPS efficiency ratings. Actual runtime may vary by ±15% depending on battery condition, temperature, and actual load characteristics.

Why does my UPS runtime seem shorter than calculated?

Several factors can reduce runtime: aging batteries lose capacity over time, high temperatures reduce battery performance, and some devices have power spikes during startup that weren't accounted for in the calculation.

What's the difference between VA and Watts in UPS ratings?

VA (Volt-Amperes) is the apparent power capacity, while Watts is the real power. Most UPS systems can deliver about 60-70% of their VA rating in watts. Always check both ratings when sizing your UPS.

How often should I replace UPS batteries?

Most UPS batteries should be replaced every 3-5 years for optimal performance. In hot environments or with frequent power outages, replacement may be needed sooner. Battery age significantly impacts runtime.

Can I connect more devices if my UPS has extra capacity?

Yes, but stay within both the VA and watt limits of your UPS. Adding more devices reduces runtime proportionally. It's recommended to keep total load under 80% of UPS capacity for best performance.

What happens if I exceed my UPS capacity?

Overloading a UPS can cause it to shut down immediately, transfer to bypass mode, or in severe cases, damage the unit. Always ensure your total load stays within the UPS ratings.

Does UPS efficiency affect runtime calculation?

Yes, UPS efficiency is crucial for runtime calculations. A more efficient UPS wastes less energy as heat, leaving more battery power available for your connected devices, thus extending runtime.

How do I find my device power consumption?

Check device labels, power adapters, or specifications for wattage. For computers, use manufacturer specs or power meters. Add up all connected devices, including monitors, routers, and other equipment.