FREE · NETWORK & IT INFRASTRUCTURE
UPS Sizing Calculator.
Size a UPS from your equipment: VA and watt rating with headroom, battery energy for the runtime you need, input current and heat.
Modern power supplies with PFC are 0.9–0.99.
Check the UPS datasheet: many models are 0.9 or 1.0.
Lead-acid capacity falls at high discharge rates; lithium keeps more.
- Load now
- 1,355 W · 1,506 VA
- Minimum rating with headroom
- 2,258 VA / 2,032 W
- Load on the chosen UPS
- 50.2 %
- Battery energy for the runtime
- 470 Wh
- Battery capacity at 48 V
- 9.8 Ah
- Input current at full rating
- 13 A
- Heat from equipment
- 4,623 BTU/h
- UPS losses while online
- ≈ 151 W
- Runtime from battery energy is approximate: lead-acid batteries deliver less at high loads (Peukert effect) and age. Check the manufacturer’s runtime chart for your load.
- Measure real draw with a power meter or the PDU; nameplate ratings are maximums and often overstate typical use.
- Laser printers and heaters have large surges and should not be on a UPS.
How to use UPS Sizing Calculator
List equipment with quantity and watts, set power factors, maximum load, growth and runtime, then read the recommended size.
How it works
Required rating = load × (1 + growth) ÷ maximum load, in both watts and VA; the smallest standard size meeting both is chosen. Battery energy = watts × runtime ÷ (inverter efficiency × usable capacity).
Example
1,355 W of servers, storage, switch and firewall need a 3,000 VA / 2,700 W UPS and about 470 Wh of battery for 15 minutes.
VA, watts and why both matter
A UPS has two ratings: volt-amperes (VA), the apparent power its electronics can carry, and watts (W), the real power it can deliver. The ratio between them is the power factor. A 3,000 VA UPS with a 0.9 power factor delivers up to 2,700 W. Your equipment must fit under both limits, so the calculator checks both and picks the smallest common size that does.
Sizing steps
- Add up the watts of every protected device. A power meter or the PDU reading is best; nameplate values are maximums.
- Convert to VA with the equipment power factor (0.9–0.99 for modern supplies).
- Add growth headroom and divide by the maximum load you accept on the UPS (80 % is common).
- Pick the smallest standard size whose VA and W ratings both exceed the result.
required W = load W × (1 + growth) ÷ max load
required VA = max(load W ÷ equipment PF, required W ÷ UPS PF) × (1 + growth) ÷ max load
battery Wh = load W × runtime h ÷ (inverter efficiency × usable battery capacity)Runtime and batteries
Runtime is a battery energy question. Fifteen minutes at 1,355 W, with a 90 % efficient inverter and 80 % usable capacity, needs about 470 Wh. Lead-acid batteries deliver less energy at high discharge rates and as they age, so use the manufacturer’s runtime chart for the final choice, or add external battery packs. The calculator also gives the battery capacity in ampere-hours at common bus voltages and the heat your equipment produces in BTU/h, which the room’s cooling must remove.
What not to connect
Laser printers, heaters and other high-surge devices can overload a UPS and drain the battery quickly. Keep the UPS for servers, storage, network equipment and anything that must shut down cleanly. To place the UPS and its load in a rack, continue with the server rack planner; for PoE switches, check their draw with the PoE budget calculator.
Questions about UPS Sizing Calculator
What size UPS do I need for 1,000 W?
With 20 % growth and an 80 % maximum load you need at least 1,500 W of capacity; at a 0.9 power factor that is a 2,000 VA unit or larger.
Online, line-interactive or standby?
Online (double-conversion) UPSs condition power continuously and suit servers; line-interactive models are common for small racks; standby models suit single desktops. The sizing arithmetic is the same.
Is UPS Sizing Calculator free, and do I need an account?
Yes. This tool is free to use in your browser without an account. Processing takes place on your device.
What are the limits and what should I check?
Runtime from battery energy is approximate; check the manufacturer’s runtime chart. Standard sizes are common ratings, not specific products. Everything is calculated in your browser; nothing is sent or probed on the network. Review the result before using it in your work.
Is my input sent to a server?
Your input is processed in your browser and is not uploaded by this tool. Files and pasted text are cleared when the page is refreshed. Normal website requests are still required to load the page and its libraries. Read the privacy explanation.