My best utilities, now on your mobile.
Access all my tools and projects fast, optimized, and in one place.
UPS Runtime Calculator
Estimate UPS battery runtime, total protected load, usable watt-hours, and recommended VA size for PCs, monitors, routers, NAS devices, and home lab hardware.
Protected load
0 min
Zoom 100%
Utilities Studio
Want this utility on your website?
Customize colors and dark mode for WordPress, Notion or your own site.
Frequently Asked Questions
How do I calculate UPS runtime?
Add the wattage of every device connected to the UPS, multiply the UPS battery watt-hours by inverter efficiency, subtract the reserve you want to keep, then divide usable watt-hours by load watts. The result in hours can be multiplied by 60 for minutes.
Why does real UPS runtime differ from the estimate?
Runtime changes with battery age, temperature, discharge rate, inverter efficiency, load spikes, and manufacturer cutoff voltage. Treat the result as a planning estimate, then verify with a controlled shutdown test.
Should I size a UPS by watts or VA?
Check both. Watts tell you the real power the UPS can deliver, while VA includes power factor. A UPS must exceed your load in watts and have enough VA headroom for the connected equipment.
How much UPS headroom should I keep?
A practical target is to keep normal load below about 70-80% of the UPS watt rating. This leaves room for startup spikes, battery aging, and future devices.
Can I plug printers or heaters into a UPS?
Avoid laser printers, heaters, and other high-surge loads unless the UPS is explicitly rated for them. They can overload the inverter and sharply reduce runtime.
# UPS Runtime Calculator: Estimate Battery Backup Time
A UPS runtime estimate answers two practical questions: how long your hardware can stay online during a power cut, and whether the UPS is large enough for the connected load. This calculator combines device wattage, battery watt-hours, inverter efficiency, power factor, and shutdown reserve so the result is closer to real planning than a simple battery-size division.# The Runtime Formula
Estimated runtime in hours is usable battery Wh divided by total load W. Usable battery Wh is not the printed battery capacity: it should be adjusted for inverter losses and the reserve you want to keep for graceful shutdown. For example, a 432Wh battery at 86% efficiency with 20% reserve provides about 297Wh of usable energy.| Input | Why it matters | Practical guidance |
|---|---|---|
| Load watts | Directly controls runtime | Measure with a wall meter when possible, especially for gaming PCs and NAS systems. |
| Battery Wh | Sets the energy pool | Use manufacturer battery data or nominal voltage multiplied by amp-hours. |
| Efficiency | Accounts for inverter loss | 80-90% is a reasonable planning range for many consumer UPS units. |
| Power factor | Converts watts to VA | Use the UPS spec if known; 0.6-0.8 is common for budget and midrange units. |
| Reserve | Keeps shutdown margin | 10-25% is sensible for controlled PC or server shutdown. |
# How Much Runtime Do You Need?
- 5-10 minutes: enough to ride through short flickers or shut down a desktop safely.
- 10-20 minutes: useful for routers, modems, NAS units, and small home lab nodes.
- 30+ minutes: better for network continuity, remote work, and locations with frequent outages.
- Several hours: usually calls for a larger battery system, not just a desktop UPS.
# Watts vs VA When Choosing a UPS
UPS product names often advertise VA, but the watt rating is the harder limit for real equipment. A 900VA UPS might only support 540W, while another 900VA model may support 600W or more. Check both ratings and keep normal operation below the maximum to avoid overload alarms, shortened battery life, and failed transfers during an outage.# Loads That Distort Runtime Estimates
- Gaming PCs can swing from low idle draw to high GPU draw in seconds.
- Monitors vary sharply with brightness, HDR mode, and panel size.
- NAS devices draw extra power during disk spin-up and rebuilds.
- Laser printers, heaters, pumps, and compressors are poor UPS loads unless specifically supported.
- Old batteries can deliver far less runtime than their original capacity suggests.
# Safe Validation Checklist
- Charge the UPS fully before testing.
- Save open work and avoid testing during critical writes or firmware updates.
- Unplug wall power, not the equipment, and watch UPS load percentage and battery estimate.
- Confirm your PC, NAS, or server receives the shutdown signal before battery is exhausted.
- Repeat the test every few months because lead-acid UPS batteries age quickly.
Bibliographic References
- [1] APC by Schneider Electric - UPS battery runtime and load behavior
https://www.se.com/us/en/work/products/tools/ups-selector/
- [2] CyberPower - Understanding watts, volt-amps, and power factor
https://www.cyberpower.com/global/en/blog/watts-vs-volt-amperes-va-key-power-ratings-for-choosing-the-right-ups
- [3] Eaton - UPS sizing and power protection fundamentals
https://www.eaton.com/us/en-us/catalog/backup-power-ups-surge-it-power-distribution/ups-buying-guide.html
More utilities from Hardware Testing & Diagnostic Tools
Lithium Battery Health Calculator
Calculate the State of Health (SoH) of your lithium battery based on cycles, voltage and temperature. Scientific guide to maximize energy longevity.
Use Tool
Dead Pixel Test and Screen Repair Tool
Check if your monitor has dead or stuck pixels and repair them with our high-frequency strobe tool online.
Use Tool
Touch Screen Tester
Draw on a full-screen canvas to test touchscreen dead zones, missed taps, edge response, palm interference, and how many simultaneous multi-touch points your phone or tablet can detect.
Use Tool
Online Gamepad & Controller Test
Test your Xbox, PlayStation or PC controller. Visualize dead zones, joystick drift and buttons.
Use Tool
Gamepad Polling Test
Measure the browser observed update rate, report interval and timing stability of a USB or Bluetooth gamepad.
Use Tool
Online Gamepad Vibration Tester
Test the haptic motors and Dual-Rumble vibration of your gamepad in the browser. Supports Xbox, DualShock, DualSense and generic controllers.
Use Tool
Online Keyboard Test & Ghosting Detector
Check if your keyboard suffers from Ghosting or Key Jamming. Real-time key visualizer and N-Key Rollover counter.
Use Tool
Keyboard Chatter Test
Detect mechanical keyboard chattering, double typing, and faulty switch bounce by checking how quickly the same key appears twice.
Use Tool
WebMIDI Keyboard Tester
Test a USB MIDI keyboard, synth, pad controller, pitch wheel, modulation wheel, note velocity, and stuck notes directly in the browser with Web MIDI.
Use Tool
Online Mouse Polling Rate Test
Check the real Hz of your mouse. Verify if your gaming mouse works at 1000Hz or more with our professional tool.
Use Tool
Mouse Double Click Test
Test every mouse button and detect unwanted double-clicks, worn switches, and contact bounce with per-button timing in your browser.
Use Tool
Mouse Scroll Test
Diagnose mouse wheel skips, reverse jumps, inconsistent scroll direction, and weak encoder signals with a local browser-based scroll wheel test.
Use Tool
Mouse DPI Analyzer
Measure your real mouse DPI online by moving the mouse a known physical distance and comparing the captured pointer movement in pixels.
Use Tool
Mouse Jitter and Angle Snapping Test
Draw raw mouse traces online to spot sensor jitter, shaky tracking, and angle snapping or prediction that makes movement artificially straight.
Use Tool
Online Tone and Frequency Generator
Generate sine, square, triangle and sawtooth waves. Test your speakers, headphones or subwoofer with frequencies from 20Hz to 20kHz.
Use Tool
Water Ejector Speaker Cleaner
Play a low-frequency 165 Hz tone to help push water, dust or loose debris out of phone, tablet and laptop speakers.
Use Tool
Subwoofer Crossover Test
Run a 200 Hz to 10 Hz sine sweep in your browser to find where your subwoofer fades, drops out, or hands off to your main speakers.
Use Tool
Speaker Phase Tester
Play in-phase and 180 degree inverted stereo test signals in your browser to check speaker polarity, wiring mistakes, and phase cancellation.
Use Tool
Microphone Test And Spectrum Analyzer
Test microphone input, live level, clipping, room noise, and frequency response locally in your browser with a private real time spectrum.
Use Tool
Private Webcam Test
Check camera permission, live video, resolution, aspect ratio, orientation and observed frame delivery before a meeting or stream.
Use Tool
Monitor Refresh Rate Detector
Instantly detect your monitor's refresh rate with precision using requestAnimationFrame. Test frame stability and compare with industry standards.
Use Tool
Monitor Ghosting Test
Test monitor ghosting, motion blur, overdrive trails, and pixel response behavior with moving bars, text, and fullscreen motion patterns.
Use Tool
Backlight Bleed and Blooming Test
Run a pure black fullscreen backlight bleed test and a draggable white local dimming blooming test for OLED, Mini LED, IPS, VA, monitors, laptops, and TVs.
Use Tool
OLED Screen Burn In Fixer
Run a fullscreen OLED burn-in fixer and LCD stuck pixel exerciser with rapid RGB color cycles, white noise, a required photosensitivity warning, and a native timer.
Use Tool
Color Accuracy Test: Spectrum Canvas
Calibrate your display with precision. Test sRGB and DCI-P3 color spaces, detect color shifts, measure accuracy with Delta E metrics, and generate professional calibration reports.
Use Tool
USB Power Budget Calculator
Check whether a USB port, charger, hub, cable, or USB-C PD profile can safely power your devices after headroom and cable voltage drop.
Use Tool
Mobile Sensor Test
Run an online gyroscope, accelerometer, motion sensor, and bubble level test on your phone to check tilt, rotation, drift, and sensor calibration problems.
Use Tool
Stereo Audio Test
Check left and right speaker channels, stereo balance, wiring direction, and headphone imaging with browser-generated test tones.
Use Tool
Web Bluetooth BLE Scanner
Scan nearby Bluetooth Low Energy devices from the browser, inspect exposed GATT service UUIDs, and test whether your IoT or wearable hardware is discoverable.
Use Tool
WebUSB Serial Monitor
Connect to USB serial hardware from the browser, read live terminal output, send commands, and debug Arduino, ESP32, RP2040, and maker boards without installing a desktop terminal.
Use Tool
Input Lag & System Latency Test
Online hardware input lag and system latency measurement tool using high-precision performance timing and frame buffer synchronization.
Use Tool
PSU Power Requirement Calculator
Estimate PC power supply requirements from component wattage, transient margin, growth headroom, and the power supply already installed.
Use Tool
Resistor Color Code Calculator
Decode resistor bands into resistance, tolerance, range, and temperature coefficient, or work backwards from a target value.
Use Tool
LED Resistor Calculator
Find the series resistor for an LED from supply voltage, forward voltage, and current, then pick the nearest E12 or E24 value and a safe wattage.
Use Tool
Audio Delay Test
Test perceived audio delay on speakers, headphones, Bluetooth devices, and video playback with a local browser pulse test.
Use Tool
Voltage Divider Calculator
Calculate a resistor divider output voltage, current, power dissipation, or the lower resistor needed for a target voltage.
Use Tool
Ohm Law and Electrical Power Calculator
An Ohm law calculator for finding voltage, current, resistance, and electrical power from any two values you know.
Use Tool