mAh to Wh Calculator
This calculator converts battery capacity from milliamp-hours (mAh) to watt-hours (Wh), using battery voltage. It’s commonly used to understand the actual energy capacity of small batteries and compare products across brands or types.
Why Convert mAh to Wh?
Milliamp-hours (mAh) measure electric charge — essentially how long a battery can supply a certain current. However, it doesn't account for voltage, which is crucial for understanding the total energy stored. Watt-hours (Wh), on the other hand, are a measure of **total energy**, and are used universally to express how much power is available to actually do work — whether powering a phone, light, or an entire system.
Converting mAh to Wh gives you a clearer, more comparable picture of battery capacity. Especially useful when:
- Comparing batteries of different voltages (e.g., lithium-ion vs lead-acid)
- Planning runtime for UPS systems, solar energy storage, or mobile electronics
- Calculating how much energy is required to charge or discharge a battery
- Evaluating product specs across brands with different labeling (some use mAh, others use Wh)
Formula: mAh to Wh
The formula to convert milliamp-hours to watt-hours is:
Wh = (mAh × V) / 1000
Where:
- mAh is milliamp-hours (battery capacity)
- V is battery voltage
- 1000 converts milliamps to amps and milliwh to wh
Example:
Convert 5000 mAh at 3.7V:
Wh = (5000 × 3.7) / 1000 = 18.5 Wh
Voltage Matters!
Many people assume that two batteries with the same mAh rating store the same energy — but that’s only true if they also have the same voltage. A 5000mAh battery at 3.7V stores far less energy than one at 12V.
- 5000mAh @ 3.7V = 18.5 Wh
- 5000mAh @ 12V = 60 Wh
That’s more than 3× the energy for the same mAh rating, proving that mAh is only part of the equation.
Typical Battery Voltages
| Device | Typical Voltage |
|---|---|
| Phone battery | 3.7 V |
| USB power bank | 3.7 V (cells), 5V (output) |
| Laptop battery | 7.2 – 11.1 V |
| Lead-acid battery | 6 V / 12 V |
| Tool battery packs | 12 – 20 V |
Real-World Examples
- Example 1: Smartphone Battery
A 3000mAh battery at 3.7V = (3000 × 3.7)/1000 = 11.1 Wh - Example 2: Laptop Battery
A 4400mAh battery at 11.1V = 4400 × 11.1 / 1000 = 48.84 Wh - Example 3: Power Bank
10,000 mAh @ 3.7 V = 37 Wh. That’s enough to charge a 3000mAh phone ~3 times (with some loss).
Why Watt-Hours Are Better for Energy Planning
Watt-hours are a true measure of stored energy. They tell you how much work a battery can do — such as how many hours it can power a 10W device (Wh ÷ Watts = hours).
- Battery runtime: Wh ÷ load watts = runtime in hours
- Backup energy sizing: Add up total load wattage and required hours, then match battery Wh
- Cross-voltage comparison: Convert all batteries to Wh, then compare directly
Common Misconceptions
- mAh is not energy: It’s charge. Without voltage, it doesn’t tell the full story.
- More mAh ≠ longer runtime always: Voltage and efficiency must be included.
- Power banks rated at 10000mAh may only provide ~60–70% usable energy: Due to voltage conversion and losses.
Frequently Asked Questions (FAQ)
Can I convert Wh to mAh?
Yes. Rearranged formula:
mAh = (Wh × 1000) / V
Is this conversion valid for all batteries?
Yes — lithium-ion, NiMH, lead-acid, etc. But make sure to use the battery’s actual nominal voltage.
Why do power banks have different Wh even if mAh is the same?
Because voltage differs. A 10,000mAh battery at 3.7V has less energy than one at 5V or 12V. Always compare using Wh.
Can I estimate charging cost using Wh?
Yes. Add up all battery Wh, convert to kWh (÷1000), and multiply by your electricity rate per kWh.
How much Wh do I need for 1 hour of runtime?
Wh = Power (W) × Time (h). So if your device uses 20W, you need at least 20Wh for 1 hour.
Conclusion
Converting mAh to Wh is essential when working with batteries, whether you’re sizing power banks, comparing product specs, or designing a solar or UPS system. mAh tells you charge capacity — but Wh tells you how much usable energy is available. This calculator provides an accurate, fast, and easy way to translate between the two — so you can plan, compare, and build your power system with confidence.