Do these 3 things before closing this tab:
1Fix the driver behind crashes, sound loss and screen glitches2Clear out junk files and repair common Windows errors3Scan for outdated or missing drivers - takes under a minuteSpecial offer. See more information about Outbyte and uninstall instructions. Please review EULA and Privacy policy.
Choose a UPS for the equipment load and the runtime you need—not because a closet is called a “server closet.” Add up the watts of the server, network gear, storage, and other devices that must stay on during an outage; check the UPS’s watt and VA limits; then use the exact model’s runtime chart to confirm it can keep that load powered long enough.
What determines the right UPS size?
Three things set the size: the combined load you want on battery, the time that load must run, and whether the UPS fits the site’s electrical and physical constraints. There is no reliable capacity recommendation based on the room label alone. Without your load, runtime target, outlet, and rack details, an exact capacity or model cannot be prescribed.
As an Amazon Associate I earn from qualifying purchases.
- Load: Count only equipment that should remain powered. Separate critical devices from equipment you could shut down or leave unprotected.
- Capacity: A UPS has both a watt rating and a volt-ampere (VA) rating. The load must fit under both limits.
- Runtime: The minutes available depend on the specific UPS and its battery configuration at your actual load.
- Fit: Verify electrical compatibility, waveform, rack dimensions, weight, and airflow before choosing a unit.
How to size a UPS for your closet
- List the equipment that needs battery power. Include the server, switches, router or firewall, storage, modem, and essential control devices as needed. Leave out equipment that does not need to stay on. Mark which loads are critical and which could be shed to extend runtime.
- Find each device’s expected operating watts and total them. Use documented operating consumption or a measured load where available. A device’s maximum nameplate draw is a conservative upper bound, but may exceed its normal operating consumption. If an installed UPS reports aggregate load, Eaton says that reading can speed up the calculation. See Eaton’s UPS sizing guide and network-closet UPS buying guide.
- Check both watts and VA. The UPS must support the load under both ratings; an attractive VA number alone is not enough. When you need to convert a watt load to VA, use the equipment power factor if known: VA = watts ÷ power factor. For example, Eaton’s 2025 UPS fundamentals handbook shows that 525 W at a 0.7 power factor equals 750 VA; at 75% of UPS capacity, that example points to a 1,000 VA unit. This is an illustration of the calculation, not a recommended closet size. See Eaton’s 2025 UPS fundamentals handbook.
- Choose and state a headroom allowance. Eaton’s network-closet guide recommends multiplying connected watts by 1.2 to allow for expansion. Its general sizing guidance separately recommends at least 15% extra VA capacity and describes assuming 15% growth over five years. These are Eaton recommendations, not universal engineering rules; specify whether your margin applies to watts or VA and why it suits your expected changes.
- Set a runtime target based on what happens during an outage. Decide whether the UPS should bridge a brief interruption, carry the load until a generator takes over, or provide time for a controlled shutdown. Eaton’s network-closet guide gives about 7–10 minutes as a commonly sought target, not a requirement or guarantee. Check the exact model’s runtime table at your planned load and battery configuration.
- Confirm electrical and physical fit. Match the UPS input voltage and plug to the site, and its output voltage and receptacles to the connected equipment. Check rack space, depth, weight, and ventilation, including the footprint of any external battery. Eaton notes that larger systems may need a higher-current receptacle and that an electrician may be needed if the required outlet is not available. That guidance is North American; local electrical requirements govern.
- Verify output waveform and server compatibility. Eaton advises using a true sine-wave UPS for servers. Confirm the selected model’s technical specifications and compatibility with the equipment rather than relying on a general product label.
How much headroom should you add?
Headroom makes room for load changes, but the calculation must say what is being increased. If following Eaton’s network-closet recommendation, multiply the connected equipment’s total watts by 1.2. If following its general sizing recommendation, add at least 15% to the required VA. Do not apply a watt margin as though it were a VA margin, or treat either recommendation as a universal standard.
Special offer. See more information about Outbyte and uninstall instructions. Please review EULA and Privacy policy.
For example, if the equipment totals 500 W, the 1.2 watt multiplier gives a planning load of 600 W. You would still need to check the chosen UPS’s VA rating and model-specific runtime at the planned load; this calculation alone does not determine a suitable capacity or runtime.
#1 Best Overall
Sale
Eaton Tripp Lite SMART1500LCD 1500VA 2U Rack Mount UPS 900W Battery Backup
- 1500VA/900W UPS: Eight NEMA 5-15R outlets provide reliable UPS battery backup & surge protection for servers, computers, and peripherals. The six-foot NEMA 5-15P input power cord ensures easy connection to compatible AC outlets
- 2U RACK MOUNT UPS: Versatile mounting options in 2U rackmount space or vertical tower with included adapter. Ideal for small servers, network devices, desktop PCs, monitors, workstations, entertainment systems, wireless routers, and more
- AUTOMATIC VOLTAGE REGULATION: AVR corrects brownouts and overvoltages from 75V to 147V back to safe 120V without using battery power. Features Modified Sine Wave (PWM) output in battery mode and Sine Wave in AC mode for low total harmonic distortion
- ADVANCED POWER FEATURES: User-replaceable internal batteries and RJ45 Ethernet port for dataline surge protection up to 100 Mbps. The large rotatable LCD screen monitors operations like voltage, runtime, load, battery, and operating mode
- FULLY SUPPORTED: Protected by a 3-Year Limited Manufacturer's Warranty and a $250,000 Ultimate Connected Equipment insurance. To best support your purchase, Eaton's expert technical team is available via phone, web, or email to address any concerns
How to compare UPS options
Compare candidates against the same load and runtime target. The watt and VA figures are separate constraints, while runtime, electrical fit, and battery support are model-specific.
| What to compare | What to verify |
|---|---|
| Output capacity | Maximum watts and VA; the load must remain within both ratings. |
| Runtime | Published minutes at your planned watt load and the stated battery configuration. |
| Waveform and compatibility | Output waveform and the manufacturer’s server compatibility information. |
| Electrical connections | Input voltage, plug, circuit and receptacle needs; output voltage and outlet types. |
| Rack and ventilation | Mounting dimensions, depth, weight, airflow, and room for any external battery. |
| Battery and management | Supported replaceable or external batteries, management features, warranty, and total cost of ownership. Confirm accessory compatibility for the exact UPS model. |
What a larger UPS or battery pack can—and cannot—do
A higher-capacity UPS may provide more output capability, but runtime still has to be checked against the model’s runtime data. Equal VA labels can conceal different watt limits: Eaton’s network-closet guide contrasts 1,000 VA units rated at 900 W and 600 W. Compare both figures rather than treating VA as a complete description of usable capacity.
Rank #2
CyberPower CP1500PFCRM2U PFC Sinewave UPS Battery Backup
- 1500VA/1000WPFC Sinewave Uninterruptible Power Supply (UPS): Uses sine wave output to provide battery backup power for Active PFC & conventional power supplies; Safeguards security systems, audio/visual equipment, and networking devices
- EIGHT NEMA 5-15R OUTLETS: Provide battery backup & surge protection for connected devices; INPUT: NEMA 5-15P right angle, 45 degree offset plug with six foot power cord
- MULTIFUNCTION, COLOR LCD PANEL: Displays immediate, detailed information on battery and power conditions; Color display alerts users to potential issues before they can affect critical equipment and cause downtime
- SHORT-DEPTH RACKMOUNT: 10.5 inches in depth, the UPS fits comfortably in short-depth rack installations where space is at a premium; AUTOMATIC VOLTAGE REGULATION: Corrects minor power fluctuations without switching to battery power, extending battery life
- 3-YEAR WARRANTY – INCLUDING THE BATTERY; $500,000 Connected Equipment Guarantee; FREE PowerPanel Management Software (Download); UL SAFETY CERTIFIED: Product has been tested in a UL certified lab and listed with UL as meeting or exceeding safety standards
A supported external battery pack can extend runtime, but it does not increase the UPS’s output power rating. Confirm the pack is approved for the exact model and that its added footprint and weight fit the installation. Eaton also gives an approximate rule of thumb that cutting the load in half may triple runtime; actual runtime varies, so use the model-specific chart for planning.
Recommended: PC Feels Slow? A Free Scan Shows What's Dragging Windows Down →Recommended: Update Every Outdated Driver on Your PC in One Scan - Free →
Special offer. See more information about Outbyte and uninstall instructions. Please review EULA and Privacy policy.
Quick Recap
Bestseller No. 2
Bestseller No. 4
Bestseller No. 5
Best Value
CyberPower OR700LCDRM1U Smart App LCD UPS Battery Backup
- 700VA/400W Smart App LCD Uninterruptible Power Supply (UPS) System uses simulated sine wave output to protect department and workgroup servers, network devices, and telecom installations without Active PFC power supplies
- SIX NEMA 5-15R OUTLETS: FOUR battery backup and surge protected outlets; Two surge protected outlets; INPUT: 15A, NEMA 5-15P with 10 foot power cord
- MULTIFUNCTION LCD PANEL: Provides runtime in minutes, battery status, power conditions, alerting users to potential problems before they can affect critical equipment and cause downtime; REMOTE MANAGEMENT: Requires optional RMCARD205 management card
- AUTOMATIC VOLTAGE REGULATION (AVR): Corrects minor power fluctuations without switching to battery power, thereby extending the life of the battery
- 3-YEAR WARRANTY – INCLUDING THE BATTERIES; $300,000 Connected Equipment Guarantee and FREE PowerPanel Business Edition Management Software (Download)
Rank #4
CyberPower CP2000PFCRM2U PFC Sinewave UPS Battery Backup
- 2000VA/1200W PFC Sine Wave Battery Backup Uninterruptible Power Supply (UPS) System designed to support active PFC and conventional power supplies; Safeguards security systems, audio/visual equipment, and networking devices
- EIGHT NEMA 5-20R OUTLETS: Provides battery backup & surge protection for connected devices; INPUT: NEMA 5-20P with six foot power cord
- MULTIFUNCTION, COLOR LCD PANEL: Displays immediate, detailed information on battery and power conditions; Color display alerts users to potential issues before they can affect critical equipment and cause downtime
- SHORT-DEPTH RACKMOUNT: 10.8 inches in depth, the UPS fits comfortably in short-depth rack installations where space is at a premium; AUTOMATIC VOLTAGE REGULATION: Corrects minor power fluctuations without switching to battery power, extending battery life
- 3-YEAR WARRANTY – INCLUDING THE BATTERY; $500,000 Connected Equipment Guarantee; FREE PowerPanel Management Software (Download); UL SAFETY CERTIFIED: Product has been tested in a UL certified lab and listed with UL as meeting or exceeding safety standards
Rank #3
Sale
CyberPower OR500LCDRM1U Smart App LCD UPS Battery Backup
- 500VA/300W Smart App LCD Uninterruptible Power Supply (UPS): Uses simulated sine wave output to provide battery backup power to protect department and workgroup servers, network devices, and telecom installations without Active PFC power supplies
- SIX NEMA 5-15R OUTLETS: Four battery backup and surge protected outlets; Two Surge protected outlets; INPUT: 15A, NEMA 5-15P straight plug with 10 foot power cord
- MULTIFUNCTION LCD PANEL: Provides runtime in minutes, battery status, power conditions, alerting users to potential problems before they can affect critical equipment and cause downtime; REMOTE MANAGEMENT: Requires optional RMCARD205 management card
- AUTOMATIC VOLTAGE REGULATION (AVR): Corrects minor power fluctuations without switching to battery power; UL SAFETY CERTIFIED: Product has been tested in a UL certified lab and listed with UL as meeting or exceeding safety standards
- 3 YEAR WARRANTY – INCLUDING BATTERIES; $300,000 Connected Equipment Guarantee
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
