Laptop Battery Life Calculator
Estimate laptop battery runtime from battery capacity (Wh or mAh + voltage) and an average power draw preset.
Wh
Usage Level
Battery Capacity
56.0 Wh
Average Power Draw
12.5 W
Estimated Runtime
4.5 hours
How to Estimate Laptop Battery Life
Enter your laptop's battery capacity — either directly in watt-hours (Wh), or as milliamp-hours (mAh) plus voltage if that's what's printed on the battery — and an average power draw for how you use the laptop. Dividing capacity by power draw gives an estimated runtime in hours.
Runtime (hours) = Capacity (Wh) ÷ Average Power Draw (W)
Example
A 56 Wh battery under moderate use (about 12.5W average draw — general browsing, documents, video) gives an estimated runtime of 56 ÷ 12.5 ≈ 4.5 hours. The same battery under heavy gaming load (around 32W) would only last about 56 ÷ 32 ≈ 1.75 hours.
Common Use Cases
- Comparing expected battery life across different laptops before buying.
- Estimating how long a laptop will last for a specific task like gaming or video calls.
- Understanding why real-world battery life falls short of a manufacturer's marketed figure.
FAQs
Where do I find my laptop's battery capacity?
Check the battery's label (often on the underside if removable), the manufacturer's spec sheet, or your operating system's battery report tool, which frequently lists both design capacity and current capacity in Wh or mWh.
Why does actual battery life vary so much from the marketed number?
Manufacturer estimates are usually measured under light, best-case conditions like video playback at low brightness. Real-world power draw jumps with screen brightness, active apps, background tasks, and especially gaming or video editing, which is why choosing a realistic preset here matters.
Does battery age affect this estimate?
Yes — batteries lose capacity over charge cycles and time. If your laptop is a couple of years old, check your OS's current (not design) capacity for a more accurate Wh figure, since a worn battery will run for less time than its original rated capacity suggests.