Backup power calculators
Free, focused tools that turn device watts and battery watt-hours into buying decisions — no account, no downloads, nothing collected.
Pick the tool for your question
Battery Runtime Calculator
Convert Wh or Ah × V into runtime for one device, with usable capacity, AC or DC efficiency, duty cycle, and reserve shown.
Best for: checking one battery and one load with assumptions you can edit, save, and share.
CalculatorPortable Power Station Calculator
Turn one device type, quantity, hours, and optional startup demand into separate battery-capacity and output requirements.
Best for: shopping for a station when you know one device type, its running watts, and required hours.
CalculatorMulti-Device Load Builder
Pick every device you need to power and get total watts, daily watt-hours, runtime by battery size, and one capacity target — with fridge duty cycles handled.
Best for: sizing a whole outage plan — several devices at once, not just one.
CalculatorSolar Recharge Calculator
Estimate what a solar panel really delivers per day and how many days a full recharge takes — using peak sun hours, not label ratings.
Best for: deciding whether a panel is worth it, and how many watts to buy.
Mission plannerCamera & Drone Power Planner
Total camera and drone battery refills, laptop time, lights, and other field energy—then check capacity and simultaneous output separately.
Best for: sizing a remote photo, video, or drone shoot without mixing watt-hours and watts.
Safety clockFridge & Freezer Outage Clock
Check the official 4-, 24-, or 48-hour closed-door planning window, then make a separate food decision from door and temperature evidence.
Best for: knowing when a fridge or freezer countdown stops being useful and the food-by-food safety check begins.
Decision wizardGear Finder
Answer six quick questions about your situation and get a suggested setup type, capacity range, and what to verify before buying.
Best for: starting from zero, before you know any of the numbers.
Which tool do I need?
- You already have (or picked) a battery. Enter its Wh or Ah × V and check it against one device with the Battery Runtime Calculator.
- You know one device type, quantity, and required hours. Check battery capacity, continuous output, and optional startup demand with the Portable Power Station Calculator.
- You need to run several things at once. Build the whole list — fridge duty cycles included — in theMulti-Device Load Builder.
- You want solar to keep it topped up. Reality-check panel size and recharge time with the Solar Recharge Calculator.
- You are powering a remote shoot. Keep camera and drone refills, laptop work, lights, battery capacity, and output limits straight in theCamera & Drone Power Planner.
- The power is already out and food is the concern. Keep planning time and food decisions separate with theFridge & Freezer Outage Clock.
- You’re starting from zero. Answer six questions in theGear Finder and get a full setup suggestion.
The five power calculators share formulas and conservative defaults — readhow we estimate for the full method. The food-safety clock instead restates fixed federal guidance and links directly to its sources.
Already know your scenario? The math is done for these
- CPAP machinesA full night of sleep therapy, sized honestly — humidifier caveats included.
- Sump pumpsSurge rating first, watt-hours second — worked for three cycling rates.
- RV & vanlifeA full daily energy budget for the road, fridge duty cycle applied.
- Starlink & home internetTerminal and router sizing for an evening, a workday, or around the clock.
Frequently asked questions
Are these calculators free to use?
Yes. All six calculators and the Gear Finder are free, run entirely in your browser, and require no account. Nothing you enter into them is collected or stored.
How accurate are the results?
They are planning estimates built on standard formulas with conservative defaults. Most general tools use 85% conversion efficiency and a 10% reserve; the creator mission planner uses editable 20–25% reserve presets for more remote-work margin. Solar estimates use 70% real-world efficiency. Real results vary with battery age, temperature, and device behavior, so treat the output as a sizing guide and always verify manufacturer specifications before buying.
What numbers do I need before I start?
Two figures cover most of the tools: your device’s power draw in watts, and a battery’s capacity in watt-hours. Watts appear on the device label or power adapter; watt-hours are on the battery spec sheet. If you don’t know a device’s wattage, the Device Wattage Library on this site lists typical ranges for common devices.