Add the appliances you want to run during a power cut to get a recommended inverter/UPS capacity (VA), and estimate how many hours your battery will back them up.
Appliance
Watt (each)
Qty
How to Use This Calculator
List the appliances you want backed up, with their wattage and quantity.
Set the inverter power factor (0.8 is a common default), battery voltage, capacity (Ah), and inverter efficiency.
Click "Calculate" to see the total load, recommended inverter VA rating, and estimated backup time.
Frequently Asked Questions
Required VA = Total Load (W) ÷ Power Factor. The result is then rounded up to the next commonly available inverter rating (e.g. 500, 700, 800, 1000, 1500 VA), since inverters aren't sold in arbitrary sizes.
Backup Time (hours) = (Battery Voltage × Battery Capacity in Ah × Inverter Efficiency) ÷ Total Load (W). For example, a 12V, 150Ah battery at 80% efficiency running a 300W load backs up for roughly (12 × 150 × 0.8) ÷ 300 = 4.8 hours.
No, it's an estimate. Real backup time also depends on battery age/health, temperature, and how deeply the battery is discharged — deeply discharging a lead-acid battery repeatedly also shortens its lifespan.