How much UPS runtime do I need?

For graceful shutdown: 5–10 minutes is sufficient for most homelab setups. For ride-through (continuing to operate through a brief outage): 15–30 minutes. For extended outages: you need a generator, not a larger UPS — battery UPS for extended backup is impractical at server load levels.

Can I add external batteries to extend runtime?

Some UPS models support external battery packs (EBMs). The APC Smart-UPS and Eaton 9PX both support this. Check the model's EBM compatibility before purchasing.

What is network management on a UPS?

A UPS with a network management card allows monitoring current load, battery health, and runtime estimates via SNMP, and can trigger graceful shutdown scripts via NUT (Network UPS Tools), PowerChute, or Eaton's IPM. Essential for unattended server rooms.

Quick answer: A homelab pulling 600 W needs roughly 670 VA of UPS (Power Factor 0.9) for a 5–10 min graceful-shutdown window — bump to 1,500 VA for 30 min ride-through.

Home & Homelab

UPS Sizing Calculator

Calculate minimum VA, required battery capacity, and get matched UPS recommendations for your homelab or server rack.

Inputs

Equipment list

Equipment	Watts	Qty

Power factor: 0.90

VA = W ÷ PF

Desired runtime

Topology preference

Has sensitive equipment (servers/NAS)

Servers with active PFC PSUs require pure sine wave output.

Minimum UPS size

0 VA

0W load · 0 VA · 15 min target

Battery Wh needed

Minimum watt rating

0 W

Product recommendations

APC Back-UPS BX1500M← Best match

$159–$220

1500 VA / 900 W

line-interactive

~Infinity min @ load

CyberPower CP1500PFCLCD

$179–$249

1500 VA / 1000 W

line-interactive

~Infinity min @ load

CyberPower OR1500LCDRT2U

$280–$380

1500 VA / 1050 W

line-interactive

~Infinity min @ load

How we calculate UPS sizing

UPS ratings are in VA (volt-amps), not watts. The calculator converts your total watt load to VA using your equipment's power factor, then determines the battery Wh capacity needed to sustain that load for your target runtime.

Required VA = Total Watts ÷ Power Factor

Most modern servers have power factors of 0.95–0.99, but networking gear and older equipment can be as low as 0.6. The default 0.9 is a safe conservative estimate. Servers with active PFC PSUs require pure sine wave UPS output.

Frequently Asked Questions

How much UPS runtime do I need?: For graceful shutdown: 5–10 minutes is sufficient for most homelab setups. For ride-through (continuing to operate through a brief outage): 15–30 minutes. For extended outages: you need a generator, not a larger UPS — battery UPS for extended backup is impractical at server load levels.
Can I add external batteries to extend runtime?: Some UPS models support external battery packs (EBMs). The APC Smart-UPS and Eaton 9PX both support this. Check the model's EBM compatibility before purchasing.
What is network management on a UPS?: A UPS with a network management card allows monitoring current load, battery health, and runtime estimates via SNMP, and can trigger graceful shutdown scripts via NUT (Network UPS Tools), PowerChute, or Eaton's IPM. Essential for unattended server rooms.

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UPS Sizing Calculator

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Reviewed April 2026

Methodology and source note

PowerSizing calculators use shared formulas, documented assumptions, and current planning inputs that are summarized on the methodology page. Use these tools for first-pass planning, comparison, and sanity checks, then confirm local code, pricing, utility tariff, and installer specifics before you buy equipment.