What Is a Free Watt-Hours to Milliamp-Hours Calculator?
A Free Watt-Hours to Milliamp-Hours Calculator (Wh to mAh Calculator) is an online battery and energy conversion tool that converts energy capacity measured in watt-hours (Wh) into charge capacity measured in milliamp-hours (mAh).
It is useful for comparing batteries, power banks, smartphones, laptops, portable electronics, solar batteries, and other energy-storage devices.
Watt-Hours to Milliamp-Hours Formula
To convert watt-hours to milliamp-hours, you need to know the battery voltage.
The formula is:
mAh = (Wh × 1,000) ÷ V
Where:
- mAh = milliamp-hours
- Wh = watt-hours
- V = battery voltage
- 1,000 = conversion from amp-hours to milliamp-hours
Example
Suppose a battery has:
- Energy capacity = 100 Wh
- Voltage = 20 V
Then:
mAh = (100 × 1,000) ÷ 20
mAh = 5,000 mAh
Therefore, a 100 Wh battery at 20 V has a nominal capacity of 5,000 mAh.
Quick Wh to mAh Examples
| Watt-Hours | Voltage | Milliamp-Hours |
|---|---|---|
| 10 Wh | 5 V | 2,000 mAh |
| 20 Wh | 10 V | 2,000 mAh |
| 37 Wh | 3.7 V | 10,000 mAh |
| 50 Wh | 10 V | 5,000 mAh |
| 100 Wh | 20 V | 5,000 mAh |
| 200 Wh | 20 V | 10,000 mAh |
| 500 Wh | 50 V | 10,000 mAh |
Why Is Voltage Important?
Wh measures energy, while mAh measures electrical charge. Voltage connects the two measurements.
The basic relationship is:
Wh = (mAh × V) ÷ 1,000
Therefore:
mAh = (Wh × 1,000) ÷ V
The same Wh rating can produce very different mAh values depending on voltage.
For example, a 100 Wh battery would be:
- At 5 V → 20,000 mAh
- At 10 V → 10,000 mAh
- At 20 V → 5,000 mAh
- At 50 V → 2,000 mAh
Why Use a Free Wh to mAh Calculator?
A Free Watt-Hours to Milliamp-Hours Calculator can help you:
- Convert battery energy into mAh
- Compare batteries with different voltage ratings
- Understand power-bank specifications
- Estimate battery capacity
- Compare portable electronic devices
- Calculate battery requirements for projects
- Evaluate solar and backup batteries
- Convert technical battery specifications
Example: Power Bank
Suppose a power bank has an energy rating of 74 Wh and a nominal voltage of 3.7 V.
mAh = (74 × 1,000) ÷ 3.7
mAh = 20,000 mAh
So a 74 Wh battery at 3.7 V is approximately 20,000 mAh.
Important: Rated Capacity vs. Usable Capacity
The calculated mAh value represents a nominal equivalent capacity based on the specified voltage. Actual usable energy may be lower because of:
- Battery discharge characteristics
- Conversion losses
- Inverter losses
- Charging and discharging efficiency
- Temperature
- Battery age
- Voltage differences during operation
For power banks and similar devices, the advertised mAh rating may be based on the internal cell voltage rather than the USB output voltage, so ratings should be compared carefully.
Wh vs. mAh
Watt-hours (Wh) measure energy.
Milliamp-hours (mAh) measure electrical charge capacity.
For meaningful battery comparisons, Wh is often more useful when batteries operate at different voltages.
In Short
A Free Watt-Hours to Milliamp-Hours Calculator converts battery energy from Wh to mAh when the voltage is known.
Formula:
mAh = (Wh × 1,000) ÷ V
For example, 37 Wh at 3.7 V = 10,000 mAh.
This calculator is particularly useful for power banks, batteries, smartphones, laptops, solar systems, portable electronics, and battery-storage projects.
