Total Load
0W
0 VA apparent power at your 0.80 power factor.
Quick Start
Load a sample setup
Pick the profile closest to your gear, then fine-tune the device list and UPS specs below.
Step 1
Add the devices to protect (your load)
Quick-add common devices, then adjust watts and quantity. Check the label on each device’s power supply for real wattage — nameplate max is usually higher than actual draw.
Quick add
Your device list
No devices yet.
Use the quick-add buttons above, load a sample setup, or add a custom device below.
⚠️ Never plug a laser printer into a UPS. Also avoid space heaters, fans with big motors, and anything with a heating element on battery outlets.
Step 2
UPS specifications & goals
Converts Watts to VA. 0.8 is standard for most consumer UPS units.
Accounts for power lost as heat during battery-to-AC conversion.
Mode A · Your UPS battery specs
Total battery string voltage. Small UPS = usually 12V; bigger units often run 24V or 48V.
Amp-hours. Typical internal SLA packs are 7Ah or 9Ah.
Internal plus any external battery packs.
Step 3
Run the numbers
Results also update automatically as you type. Saving keeps your inputs on this device only — nothing is sent anywhere.
Results
Your UPS numbers
Estimated Runtime
0.0min
0h 0m on a 0 Wh effective battery bank.
Tick marks a 60-minute target
Waveform Verdict
Add devices to see a waveform recommendation.
System Notes & Warnings
This tool provides general estimates for planning purposes only. Actual runtime depends on battery age, temperature, load profile, and unit design. Always check manufacturer specifications for exact runtimes before relying on a UPS for critical equipment.
Plain English
What these numbers mean
Gear Plan
Your shopping checklist
Generated from your current inputs. Use it as a starting point and always verify specifications before buying.
Gear
Recommended Equipment Categories
Affiliate disclosure: As an Amazon Associate, Gadget Earth may earn from qualifying purchases. Product availability and prices change frequently. We link to broad product categories — always compare specifications and reviews yourself.
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The beginner’s guide to UPS backup power
How to Size a UPS for Your PC or Network
Sizing a UPS is a four-step process, and this calculator does the math for you:
- Add up your load in watts. List everything that must stay on: PC, monitors, router, modem, NAS, console. Use real measured or typical wattage, not nameplate maximums, for a realistic number.
- Convert to VA. Divide total watts by the power factor (0.8 is a safe planning default). That is the apparent load your UPS must also support.
- Pick a UPS rated above both numbers. Add 20–25% headroom so the unit is not running at its limit, and confirm the unit’s watt rating — not just VA — covers your load.
- Match runtime to your goal. A few minutes covers graceful shutdown. Thirty-plus minutes means working through outages, which needs bigger or extra battery packs.
Watts vs. VA: The Biggest UPS Buying Mistake
UPS marketing leads with VA because the number looks bigger. But the watt rating is the hard limit for most modern electronics loads. A 1500VA unit rated for 900W will still overload and shut down at 1,000W, even though “1000W < 1500VA” looks fine on paper. Before you buy, find both ratings in the spec sheet (often labeled “output power” in W and “output VA”), and make sure your load fits under both with headroom. This single check prevents the most common UPS disappointment: a unit that trips immediately under a gaming PC or server.
Pure Sine Wave vs. Simulated Sine Wave (Active PFC Explained)
Wall power is a smooth sine wave. Budget UPS units approximate it with a stepped, “simulated” waveform when on battery. Most simple loads (routers, modems, basic monitors) do not care. Modern PC power supplies with Active PFC (power factor correction) can be pickier: some shut down instantly or stress components on stepped waves. Gaming PCs, workstations, servers, NAS devices, and quality AV gear almost all use Active PFC today. The rule is simple: if the equipment is expensive or data-critical, buy a pure sine wave UPS. The price difference is cheap insurance.
Why You Should Never Plug a Laser Printer into a UPS
A laser printer’s fuser draws a huge burst of power — often 600–1,200+ watts — each time it heats up, which can happen mid-print. That spike can overload the UPS inverter, crash your other protected devices, and stress the battery hard. UPS manufacturers explicitly exclude laser printers for this reason. Plug the printer straight into the wall or into the surge-only outlets of a power strip, and keep the UPS battery outlets for your computer and network gear only. Same goes for heaters, fans with large motors, and anything with a heating element.
Sealed Lead Acid (SLA) vs. Lithium UPS Batteries
SLA is the traditional choice: inexpensive, widely available in standard sizes (like 12V 9Ah packs with F1/F2 terminals), and recyclable — but heavier, with a typical 3–5 year life that shortens in warm rooms. Lithium UPS batteries (and lithium-based UPS units) cost more up front but can last roughly 2–3× longer, weigh far less, and tolerate more charge cycles — attractive for rack setups and hot closets. One caveat: do not swap lithium cells into a UPS designed for SLA without confirming compatibility, since charging profiles differ. For most home users, quality SLA with regular replacement remains the practical default.
FAQ
Frequently asked questions
How long will a 1500VA UPS last?
It depends entirely on the load. A typical 1500VA unit with one or two 9Ah batteries might run a router and modem for well over an hour, a laptop and monitor for roughly 15–30 minutes, and a full gaming PC under heavy load for only a few minutes. Runtime scales with battery capacity and drops as your wattage draw increases. Enter your actual load in the calculator above for a realistic estimate.
Do I need a Pure Sine Wave UPS for my gaming PC?
It is strongly recommended. Most modern gaming PCs and quality power supplies use Active PFC, which can behave unpredictably on simulated (stepped) sine wave power — sometimes shutting down immediately when the UPS switches to battery. Servers, NAS devices, and AV equipment are also safer on pure sine wave. Simulated sine wave units are generally fine for simple loads like routers and modems.
Can I plug a laser printer into my UPS?
No. Laser printers draw huge power spikes — often 600 to 1,200 watts or more — when the fuser heats up. That surge can overload a UPS, crash the inverter, and stress the battery. Plug laser printers directly into the wall or into the surge-only outlets of a power strip, never into a UPS battery outlet.
What is the difference between Watts and VA?
Watts measure real power — the energy actually doing work. VA (volt-amperes) measure apparent power, which includes power that sloshes back and forth due to the power factor of the equipment. UPS units are marketed by VA but are also limited by their watt rating, and the watt limit is usually 50–70% of the VA number. Always check both ratings before buying.
How often should I replace my UPS batteries?
Sealed lead acid UPS batteries typically last 3–5 years depending on temperature, charge cycles, and quality. Hot environments shorten life significantly. If your runtime drops noticeably or the UPS fails a self-test, replace the battery pack. Many units have a replace-battery indicator.
Can a UPS protect against lightning strikes?
No consumer UPS or surge protector can guarantee protection against a direct or very close lightning strike. UPS surge suppression helps with smaller spikes, sags, and noise, but during serious storms the safest option for sensitive gear is to unplug it from the wall — including network and coax lines.
Is a portable power station better than a UPS?
They solve different problems. A UPS is designed to bridge outages instantly, usually in milliseconds, and condition power continuously. A portable power station stores far more energy and can run devices for hours, but many are slower to pass power through and not all are rated for seamless switchover. For protecting a running PC from blips, use a UPS. For long outages, a power station is a good complement.
How do I safely dispose of old UPS batteries?
Never put UPS batteries in household trash and never incinerate them. Sealed lead acid batteries are highly recyclable — drop them at battery recycling centers, electronics recyclers, or participating retailers. Lithium packs need special handling too: tape the terminals and use a certified recycler. Check your local regulations for drop-off locations.
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