mAh to Wh Calculator
Convert battery capacity from milliamp-hours (mAh) to watt-hours (Wh) instantly using voltage.
Energy Comparison Chart
Comparing your input to standard battery capacities (Wh)
| Battery Type | Nominal Voltage (V) | Typical mAh | Calculated Wh |
|---|---|---|---|
| AA Alkaline | 1.5V | 2500 mAh | 3.75 Wh |
| Li-ion (18650) | 3.7V | 3000 mAh | 11.10 Wh |
| Smartphone | 3.85V | 4500 mAh | 17.33 Wh |
| Laptop (3-cell) | 11.1V | 4400 mAh | 48.84 Wh |
What is a mAh to Wh Calculator?
A mAh to Wh Calculator is an essential tool for engineers, hobbyists, and tech enthusiasts to determine the total energy storage capacity of a battery. While milliamp-hours (mAh) tell you how much current a battery can deliver over time, watt-hours (Wh) provide a more accurate measure of the actual work or energy the battery can perform. This is crucial when comparing batteries of different voltages.
Anyone dealing with portable electronics, solar power storage, or drone batteries should use a mAh to Wh Calculator. A common misconception is that a higher mAh always means a longer-lasting battery. However, without considering the voltage, mAh is only half the story. For instance, a 10,000mAh power bank at 3.7V has significantly less energy than a 10,000mAh car battery at 12V.
mAh to Wh Calculator Formula and Mathematical Explanation
The conversion from mAh to Wh is based on Joule's Law. To find the energy in watt-hours, you must multiply the charge in milliamp-hours by the potential difference in volts and then divide by 1,000 to convert "milli" units to standard units.
The Formula: Wh = (mAh × V) / 1000
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| mAh | Milliamp-hours (Electric Charge) | mAh | 100 – 50,000 |
| V | Voltage (Potential Difference) | Volts (V) | 1.2 – 48.0 |
| Wh | Watt-hours (Energy) | Wh | 0.5 – 500 |
Practical Examples (Real-World Use Cases)
Example 1: Smartphone Battery
Most modern smartphones use a 3.85V lithium-polymer battery. If your phone is rated at 4,000 mAh, the calculation using the mAh to Wh Calculator logic would be: (4000 × 3.85) / 1000 = 15.4 Wh. This tells you the total energy available to power the screen and processor.
Example 2: Power Bank Capacity
You buy a power bank labeled "20,000 mAh". These are almost always rated at the internal cell voltage of 3.7V. Using our mAh to Wh Calculator: (20,000 × 3.7) / 1000 = 74 Wh. This is important because airlines often limit carry-on batteries to 100 Wh.
How to Use This mAh to Wh Calculator
- Locate the mAh rating on your battery label or spec sheet.
- Find the nominal voltage (V). For Li-ion, this is usually 3.6V or 3.7V.
- Enter the mAh value into the first input field.
- Enter the Voltage value into the second input field.
- The mAh to Wh Calculator will automatically update the results, showing you the energy in Wh, Joules, and Ah.
- Use the "Copy Results" button to save your data for technical documentation.
Key Factors That Affect mAh to Wh Results
- Nominal vs. Actual Voltage: Batteries start at a higher voltage when full and drop as they discharge. The mAh to Wh Calculator uses nominal voltage for a standard average.
- Discharge Rate: High current draw can reduce the effective capacity due to internal resistance (Peukert's Law).
- Temperature: Extreme cold or heat significantly impacts chemical efficiency and energy output.
- Battery Age: As batteries cycle, their internal resistance increases, leading to lower actual Wh than the label suggests.
- Conversion Efficiency: When using a power bank, the internal circuitry must boost 3.7V to 5V (USB), which incurs energy loss.
- Depth of Discharge (DoD): Most systems don't use 100% of the Wh to protect the battery's lifespan.
Frequently Asked Questions (FAQ)
Can I use this for Wh to mAh conversion?
This specific tool is a mAh to Wh Calculator. To go the other way, use the formula: mAh = (Wh × 1000) / V.
Why do airlines care about Wh instead of mAh?
Watt-hours measure the total energy (potential heat/fire risk), whereas mAh doesn't account for voltage. A high-voltage battery with low mAh can still contain massive energy.
What voltage should I use for a 12V lead-acid battery?
While it's called "12V", the nominal voltage is usually 12.0V or 12.6V. Use 12V for a standard mAh to Wh Calculator estimation.
Is 1000 mAh equal to 1 Ah?
Yes, "milli" means one-thousandth. So 1,000 milliamp-hours equals exactly 1 amp-hour.
Does the mAh to Wh Calculator work for AC power?
No, this is designed for DC batteries. AC power involves power factors and RMS voltage which require different calculations.
How many Wh is a 5000mAh 3.7V battery?
Using the mAh to Wh Calculator: (5000 * 3.7) / 1000 = 18.5 Wh.
What is the difference between Wh and Joules?
Both measure energy. 1 Watt-hour is equal to 3,600 Joules. Our calculator provides both for convenience.
Why does my power bank feel like it has less Wh than calculated?
Voltage conversion (boosting 3.7V to 5V) usually has an efficiency of 80-90%, meaning you lose some Wh as heat.
Related Tools and Internal Resources
- Wh to mAh Converter – Convert energy back to charge capacity.
- Battery Capacity Calculator – Estimate how long your battery will last under load.
- Lithium Battery Energy Guide – Deep dive into Li-ion chemistry and energy density.
- Voltage to Watt-Hours – Learn how voltage impacts total energy storage.
- Power Bank Capacity Guide – Understanding real-world vs. rated capacity.
- Battery Life Estimator – Calculate runtime for your specific devices.