UPS Sizing Calculator
How big a UPS does your homelab actually need? Enter what you want protected, and this works out the wattage with proper headroom, then filters to units that will not upset a modern power supply and that can tell your server to shut down cleanly.
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What the UPS has to carry
Your load
59 W
- Minimum UPS rating, 70% ceiling
- 85 W
- Comfortable rating, 60% load
- 99 W
Pure sine wave units that fit
- CyberPower CP1000PFCLCD — 600W, ~$180 Runs at 10% of capacity · Official NUT DDL entry, usbhid-ups Runtime at your load: the vendor does not publish a figure we can scale, so we do not guess one
- CyberPower CP1500PFCLCD — 1000W, ~$240 Runs at 6% of capacity · Official NUT DDL entry, usbhid-ups; PowerPanel for Linux Estimated runtime at your load: about 171 minutes Best watts per dollar of the pure sine wave units.
- Vertiv Liebert PSI5-750MT120 — 675W, ~$255 Runs at 9% of capacity · Not verified against NUT Runtime at your load: the vendor does not publish a figure we can scale, so we do not guess one
- APC Back-UPS Pro BR1500MS2 — 900W, ~$300 Runs at 7% of capacity · NUT usbhid-ups and apcupsd, both confirmed · sold by Amazon directly Runtime at your load: the vendor does not publish a figure we can scale, so we do not guess one The only unit here confirmed sold by Amazon directly.
- Eaton Tripp Lite SMART1500LCDT — 900W, ~$311 Runs at 7% of capacity · NUT DDL entry, usbhid-ups Runtime at your load: the vendor does not publish a figure we can scale, so we do not guess one A historical NUT crash bug is fixed in current NUT builds.
- Eaton 5SC750 — 525W, ~$335 Runs at 11% of capacity · NUT DDL entry, 5SC_750 Runtime at your load: the vendor does not publish a figure we can scale, so we do not guess one Expensive per watt against the CyberPower units.
What we ruled out, and why
- APC Back-UPS BX850M — Stepped sine wave. Active-PFC power supplies, which modern mini PCs and NAS boxes use, can misbehave on it.
- Eaton 5S700LCD — Stepped sine wave. Active-PFC power supplies, which modern mini PCs and NAS boxes use, can misbehave on it.
- Eaton Tripp Lite OMNI900LCD — Stepped sine wave. Active-PFC power supplies, which modern mini PCs and NAS boxes use, can misbehave on it.
- Use measured wall draw, not the nameplate rating on the power brick. Nameplate is the rated maximum and a mini PC that says 120W often idles near 15W.
- Spinning drives pull noticeably more during spin-up than at idle. Size against the spin-up figure if everything starts at once after an outage.
The two things that disqualify a UPS for a homelab
Most UPS buying advice stops at watts and runtime. For a mini PC homelab, two other properties matter more, and neither is on the front of the box.
The first is waveform. Cheap units output a stepped or simulated approximation of mains rather than a true sine wave. Modern power supplies use active power factor correction, and active-PFC supplies can behave badly on a stepped waveform — the failure mode people report is the supply cutting out or buzzing on battery, which is precisely when you needed it to work. Mini PCs, NAS boxes and most current desktop supplies are active PFC, so the calculator above simply refuses to recommend a stepped unit and tells you which ones it excluded.
The second is clean shutdown. A UPS that keeps the box alive for twenty minutes and then drops it mid-write has bought you nothing. You want the server to notice the outage, wait, and shut itself down while power remains. On Linux that is Network UPS Tools, which Proxmox and TrueNAS both build on, and the practical question is whether your model has a working NUT driver. The `apcupsd` alternative is APC-only. Every unit in the calculator lists what it supports.
Why the calculator refuses to fill your UPS
A UPS should not be run near its rating. The working rule is to stay under about 70% of the watt figure, and 60% is a more comfortable target because it leaves room for the box you add next year. Running close to the limit shortens battery life, and the published runtime figures assume a fresh battery in good conditions, so real numbers land lower.
Runtime is also not linear, which surprises people. Halving the load does not double the runtime — it multiplies it by roughly three to four times. That is why a modestly larger unit often buys far more time than the price difference suggests, and it is the one place where spending up is genuinely efficient.
Size for the shutdown, not for the outage
Five to ten minutes of runtime covers a clean shutdown on almost any homelab. Buying thirty minutes or more means you are paying for ride-through — keeping services online through a brief cut — and that is a different and much more expensive goal. Unless something genuinely must stay up, size for the shutdown window and let the box come back when power does.
One more trap worth naming: size against measured draw, not the nameplate. The rating on a power brick is the maximum it can deliver, not what the machine uses. A mini PC with a 120W adapter often idles near 15W. Ourpower cost calculator uses the same sourced idle and load figures if you want the annual running cost alongside the sizing.
What to protect
Put the server, the NAS, and the network gear that carries them on battery outlets. There is no point in the server surviving if the switch it talks through does not. Monitors, printers and anything with a heating element belong on the surge-only outlets, or on a different strip entirely.
If the homelab includes spinning drives, remember that they draw noticeably more during spin-up than at idle, and after an outage everything starts at once.
Related reading
For the machines themselves, see ourbest mini PC for a home server picks and themini PC power consumption guide. If the UPS is going in a rack, ourNAS mini PC roundup covers the boxes that usually sit alongside it, and theTrueNAS hardware calculator sizes the storage side.
How these figures are sourced
Model specifications, waveform, and NUT or apcupsd support were verified against vendor documentation and the Network UPS Tools hardware compatibility list, and every Amazon listing was validated on August 25, 2026. Mini PC idle figures come from our sourced power dataset. Runtime estimates are shown only for units where the vendor publishes a runtime figure we can scale from; where no such figure exists the calculator says so rather than inventing one. Prices move constantly, so treat every figure as approximate and check the current price before buying.