UPS Load & Runtime Calculator
Add your IT equipment — servers, switches, workstations and peripherals — to build a live load estimate. Read the recommended UPS rating with a 25% safety margin, then use the runtime calculator to estimate how long your battery will last at that load, or to work out what capacity you need for a target runtime.
Build your load
Preset wattages are typical/indicative — replace them with nameplate or measured figures where known. Assumes a power factor of 0.9 for VA conversion.
UPS sizing
Runtime calculator
Runtime estimates are indicative. Real runtime depends on battery age, temperature, and the manufacturer’s discharge curve (non-linear at high loads — Peukert effect). Always check the manufacturer’s runtime chart.
= 84 Wh
Use — Guide
How to use this tool
- Add each device in your server room, comms cabinet or office using the "Add device" button. Select the device type from the preset list — the typical wattage fills in automatically. Replace it with the nameplate or measured wattage wherever you have it.
- Set the quantity for each device. The total load in Watts and VA updates live as you go.
- Read the UPS sizing panel: the minimum rating covers your bare load; the recommended rating adds 25% headroom so the UPS runs comfortably within its safe operating range.
- Use the Runtime calculator to estimate how long your existing battery will last at this load, or to work backwards from a target runtime to find the battery capacity you need.
- If you already have a UPS, enter its rated wattage in the optional check field — the tool will flag if your load is eating into the safety margin.
- Ready to spec real power protection? Talk to Peritus Digital — we size, supply and install UPS systems for server rooms and comms cabinets across the Hunter Region.
FAQ — Questions
Frequently asked questions
01What is the difference between VA and watts for a UPS?
Watts (W) measure real power — the actual energy consumed by your equipment. Volt-amperes (VA) measure apparent power, which includes reactive power drawn by capacitors and inductors inside power supplies. For modern IT equipment with switch-mode power supplies, the power factor is typically 0.9–0.95, so VA = Watts ÷ power factor and VA will always be somewhat higher than Watts. UPS units are rated in both; always ensure both your watt and VA loads sit within the UPS rating. This calculator assumes a power factor of 0.9, which is a conservative default for mixed IT loads.
02How much headroom should a UPS have?
The standard recommendation is to load a UPS to no more than 80% of its rated capacity. This gives headroom for transient inrush currents when devices power on, protects the UPS from thermal stress and extends both its operational life and its battery service life. Our calculator applies 25% headroom above your measured load, which places the load at roughly 80% of the recommended UPS size. For critical infrastructure, 50–60% loading (i.e. a larger safety margin) is common.
03Why is my real runtime shorter than the estimate?
Several factors shorten real runtime below a simple linear estimate. Battery capacity decreases with age — a lead-acid battery loses 20–30% capacity within 3–5 years even with good maintenance. Temperature matters: batteries lose capacity below 20°C and degrade faster above 25°C. High load shortens runtime disproportionately due to the Peukert effect — internal resistance increases under heavy current draw. The battery manufacturer's runtime chart (plotted for different loads) is the authoritative source. Always treat this calculator's output as an indicative estimate and cross-check with the manufacturer's data for your specific battery and load.
04Does Peritus Digital supply and install UPS systems?
Yes. Peritus Digital sizes, supplies and installs UPS systems for server rooms, comms cabinets and critical workstations across the Hunter Region. We work with leading UPS brands and can advise on runtime requirements, battery replacement schedules, safe shutdown software integration and — for larger installations — generator handover and maintenance bypass configurations. Contact us for a no-obligation assessment.
More — Keep exploring
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Want hands-on help, not just a check? Explore ourManaged IT & Support service.
Need power protection advice?
Speccing a UPS for a server room or comms cabinet? Peritus Digital sizes, supplies and installs the right solution.
From small office UPS units to rack-mounted redundant arrays with safe-shutdown software and monitoring, our Newcastle team designs power protection that suits your load, runtime requirements and budget — and stays on top of battery health over time.