Battery Capacity Calculator
Convert battery capacity between Ah, Wh, and kWh — plus see runtime estimates for common appliances at your battery's usable capacity.
| Appliance | Watts | Runtime |
|---|---|---|
| Phone charging (20W USB-C) | 20W | 3d 14h |
| Laptop (65W) | 65W | 1d 3h |
| LED lighting (5 bulbs, 10W ea) | 50W | 1d 11h |
| Internet router | 15W | 4d 19h |
| 12V compressor fridge (40W avg) | 40W | 1d 19h |
| Standard household fridge | 150W | 11h 31m |
| LED TV 55" | 110W | 15h 43m |
| Box fan | 75W | 23h 2m |
| Portable CPAP machine | 30W | 2d 10h |
| Sump pump (running) | 400W | 4h 19m |
| Window AC (5,000 BTU) | 500W | 3h 27m |
| Mini split (9,000 BTU) | 900W | 1h 55m |
How to Use This Calculator
Enter Ah or Wh — whichever you know
Click the toggle to choose whether you're starting with amp-hours (Ah) or watt-hours (Wh). Ah is printed on most battery labels (100Ah, 200Ah). Wh is sometimes listed in spec sheets or on all-in-one battery systems. The calculator converts between all three units — Ah, Wh, and kWh — instantly.
Set the battery voltage
The voltage is the critical multiplier: Wh = Ah × Voltage. A 100Ah battery at 12V holds 1,200 Wh. The same 100Ah capacity at 48V holds 4,800 Wh — 4× more energy despite the same Ah rating. This is why you can't compare batteries by Ah alone without knowing the voltage.
Set depth of discharge
The depth of discharge determines your usable capacity — what you can actually draw out. At 80% DoD, a 200Ah 12V battery (2,400 Wh) gives you 1,920 Wh. At 50% DoD (lead-acid), the same battery gives only 1,200 Wh. The runtime table below the conversions shows how long each appliance can run from your usable Wh.
Read the runtime table
The runtime estimates assume 90% inverter efficiency for AC appliances. DC loads (12V fridge, LED strips connected directly) run slightly longer since there's no inverter loss. Use the table as a quick reference to understand what your battery can realistically power.
The Formula
Key relationships to memorize: Ah tells you current × time (how long you can draw a given current). Wh tells you power × time (the total energy). Always multiply Ah by voltage to get Wh before comparing batteries at different voltages.
Example
Understanding a 200Ah 12V battery
A 200Ah 12V LiFePO4 battery (80% DoD, 90% inverter efficiency):
Runtime for common appliances
The same battery at a 48V system voltage would hold 9,600 Wh (4× more energy) despite having the same 200Ah rating — because the higher voltage carries more power per amp. This is why 48V systems are more efficient for high-power applications.