Your laptop battery life depends on what you are actually doing — not the "up to 12 hours" the manufacturer claims. That spec was tested with the screen at 30% brightness doing nothing but displaying a static webpage. This calculator gives you a realistic estimate based on your actual usage pattern.
Laptop Power Draw by Usage Type
| Activity | Typical Power Draw | Runtime on 56Wh |
|---|---|---|
| Idle (screen on, nothing running) | 5-8W | 7-11 hours |
| Web browsing / email | 10-15W | 3.5-5.3 hours |
| Document editing (Word/Sheets) | 8-12W | 4.4-6.6 hours |
| Video streaming (YouTube/Netflix) | 12-20W | 2.7-4.4 hours |
| Video calls (Zoom/Teams) | 15-25W | 2.1-3.5 hours |
| Photo editing (Lightroom) | 20-35W | 1.5-2.7 hours |
| Software development (compiling) | 25-45W | 1.2-2.1 hours |
| Gaming (GPU active) | 50-100W | 34-67 minutes |
| AI/ML training | 60-120W | 28-56 minutes |
These figures assume a typical ultrabook with a 56Wh battery and integrated graphics. Gaming laptops with larger batteries (80-100Wh) last proportionally longer at each activity level.
How to Find Your Laptop's Battery Specs
- Windows: Open a Command Prompt and type
powercfg /batteryreport. The generated HTML report shows your battery's design capacity in mWh. Divide by 1,000 to get Wh. It also shows current full charge capacity vs original — a measure of battery health. - Mac: Hold Option and click the Apple menu, then choose System Information. Under Power, find "Full Charge Capacity (mAh)" and voltage. Multiply mAh by voltage and divide by 1,000 for Wh. Or check Apple's spec page for your model's Wh rating.
- Check real-time power draw: On Windows, install HWMonitor or check Task Manager's "Power Usage" column. On Mac, Activity Monitor shows energy impact per app. These tools reveal which apps drain your battery fastest.
Frequently Asked Questions
Calculate what your laptop costs to run per month with the <a href="/electrical/kwh-calculator">kWh calculator</a>.
Laptop battery runtime is a moving target that changes with every app you open, every browser tab, and every year of battery aging. The calculation above gives you a baseline — then adjust your habits (screen brightness, background apps, power mode) to get the most out of the capacity you have.
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Written and maintained by Dan Dadovic, Developer & Off-Grid Energy Enthusiast. On the energy side, Dan has hands-on experience with residential solar panel installation, DIY battery bank construction, off-grid power systems, and wind power — all from building and maintaining his own systems..
Disclaimer: Calculator results are estimates based on theoretical formulas. Actual performance varies with temperature, battery age, load patterns, and equipment condition. For critical electrical work, consult a licensed electrician.