nicole nielsen
Understanding battery specifications can be confusing because manufacturers use several different units to describe capacity. Two of the most common are watt-hours (Wh) and milliamp-hours (mAh).
If you have a battery specification in watt-hours but need to know the equivalent milliamp-hour capacity, you can perform a simple calculation when the voltage is known.
This guide explains how to convert watt-hours to milliamp-hours, the formula behind the conversion, practical examples, common mistakes, and how a FREE TOOLS Watt-Hours to Milliamp-Hours Calculator can make the process faster.
What Does Watt-Hour Mean?
A watt-hour is a unit of energy.
One watt-hour represents one watt of power delivered or consumed for one hour.
The relationship is:
Wh = W × hours
For example, a device consuming 10 watts for 5 hours uses:
10 × 5 = 50 Wh
Battery manufacturers can use Wh to communicate the amount of energy stored in a battery.
What Does Milliamp-Hour Mean?
A milliamp-hour measures electrical charge.
The abbreviation is:
mAh
The “milli” prefix means one-thousandth.
Therefore:
1,000 mAh = 1 Ah
A 4,000 mAh battery theoretically represents 4 amp-hours of charge capacity.
However, mAh by itself does not describe total energy unless voltage is also known.
The Relationship Between Wh and mAh
The relationship between energy and charge can be expressed as:
Wh = V × Ah
Since:
Ah = mAh ÷ 1000
we can write:
Wh = V × mAh ÷ 1000
Rearranging the formula gives:
mAh = Wh × 1000 ÷ V
This is the main formula used by a Watt-Hours to Milliamp-Hours Calculator.
Simple Wh to mAh Formula
The formula is:
mAh = (Wh × 1000) / Voltage
For example:
Wh = 24
Voltage = 12 V
Therefore:
24 × 1000 ÷ 12 = 2,000 mAh
So 24 Wh at 12 volts corresponds to 2,000 mAh.
Step-by-Step Conversion
Let’s work through a complete example.
Suppose a rechargeable battery has:
- Energy = 36 Wh
- Voltage = 12 V
First multiply Wh by 1,000:
36 × 1,000 = 36,000
Then divide by voltage:
36,000 ÷ 12 = 3,000
Therefore:
36 Wh at 12 V = 3,000 mAh
Example: 50 Wh Battery
Suppose a battery is rated at 50 Wh and has a nominal voltage of 10 V.
Formula:
50 × 1000 ÷ 10
Result:
5,000 mAh
Therefore, 50 Wh at 10 V is equivalent to 5,000 mAh.
Example: 75 Wh Battery
75 Wh at 15 V:
75 × 1000 ÷ 15
= 5,000 mAh
Again, the result depends on voltage.
Example: 100 Wh Battery
100 Wh at 20 V:
100 × 1000 ÷ 20
= 5,000 mAh
This illustrates an important principle: increasing voltage decreases the mAh value for the same Wh energy.
Why the Same Wh Can Have Different mAh
Imagine three batteries, each containing 100 Wh.
Battery A: 5 V
100 × 1000 ÷ 5 = 20,000 mAh
Battery B: 10 V
100 × 1000 ÷ 10 = 10,000 mAh
Battery C: 20 V
100 × 1000 ÷ 20 = 5,000 mAh
All contain 100 Wh, but their mAh ratings are different.
This is because mAh measures charge and Wh measures energy.
Wh to mAh Calculator for Electronics
Electronic engineers and hobbyists frequently need to convert between these units.
Common applications include:
- Microcontroller projects
- Arduino projects
- Raspberry Pi systems
- Portable electronics
- Battery-powered sensors
- IoT devices
- LED systems
- Robotics
- Drones
- Portable displays
- USB equipment
- Wireless devices
Suppose an electronics project needs 15 Wh of energy at 5 V.
The equivalent charge capacity is:
15 × 1000 ÷ 5 = 3,000 mAh
This provides a useful reference when selecting a battery.
Wh to mAh for Smartphones
Smartphone batteries are commonly advertised in mAh.
Suppose a smartphone battery is rated at:
5,000 mAh
and its nominal voltage is approximately:
3.7 V
Its approximate energy is:
5,000 × 3.7 ÷ 1000 = 18.5 Wh
This demonstrates how mAh can be converted into Wh.
If you encounter a smartphone battery specification in Wh, you can reverse the process to estimate its mAh rating.
Wh to mAh for Power Banks
Power banks are another common application.
Suppose a power bank contains approximately:
20 Wh
of stored energy.
Using a nominal battery voltage of 3.7 V:
20 × 1000 ÷ 3.7 ≈ 5,405 mAh
Therefore, the internal battery capacity would be approximately 5,405 mAh.
Real power-bank output is affected by conversion efficiency, so the actual usable output may be lower.
Wh to mAh for Laptops
Laptop manufacturers frequently specify batteries using Wh.
Suppose a laptop battery has:
70 Wh
and a nominal voltage of:
11.55 V
Then:
70 × 1000 ÷ 11.55 ≈ 6,061 mAh
The exact battery specification should always be checked against the manufacturer’s information.
Wh to mAh for Solar Systems
Solar batteries may be specified using energy storage in Wh.
Suppose a small solar battery stores:
240 Wh
at:
12 V
Then:
240 × 1000 ÷ 12 = 20,000 mAh
This is also:
20 Ah
because 20,000 mAh ÷ 1,000 = 20 Ah.
Wh to mAh for Electric Vehicles
Large batteries in electric vehicles are usually described using kWh rather than mAh.
However, the same basic electrical relationship applies.
For example:
1 kWh = 1,000 Wh
Suppose a battery contains:
5 kWh
That equals:
5,000 Wh.
At 400 V:
5,000 × 1000 ÷ 400 = 12,500 mAh
or:
12.5 Ah
For large batteries, Ah is generally more practical than mAh.
Converting kWh to mAh
If your battery is listed in kWh, first convert kWh to Wh.
For example:
2 kWh = 2,000 Wh
Then:
mAh = 2,000 × 1000 ÷ voltage
At 48 V:
2,000 × 1000 ÷ 48 ≈ 41,667 mAh
or approximately 41.67 Ah.
Understanding Nominal Voltage
Battery voltage is not always constant.
A rechargeable battery may have:
- Nominal voltage
- Fully charged voltage
- Minimum operating voltage
- Cutoff voltage
When converting a manufacturer’s Wh and mAh ratings, use the voltage associated with the rating, generally the nominal voltage when estimating battery capacity.
Using a maximum charging voltage instead may produce a misleading result.
Why Online Calculators Are Useful
An online calculator can eliminate repetitive arithmetic.
For example, if you need to compare twenty batteries, entering each value into a calculator can be easier than repeatedly writing:
Wh × 1000 ÷ V
A free calculator can also reduce simple arithmetic errors.
Wh to mAh Conversion Table
| Energy | Voltage | Equivalent Capacity |
|---|---|---|
| 10 Wh | 3.7 V | 2,703 mAh |
| 10 Wh | 5 V | 2,000 mAh |
| 20 Wh | 3.7 V | 5,405 mAh |
| 20 Wh | 5 V | 4,000 mAh |
| 30 Wh | 12 V | 2,500 mAh |
| 50 Wh | 12 V | 4,167 mAh |
| 100 Wh | 12 V | 8,333 mAh |
| 100 Wh | 24 V | 4,167 mAh |
| 500 Wh | 48 V | 10,417 mAh |
| 1,000 Wh | 48 V | 20,833 mAh |
Wh to Ah vs Wh to mAh
Sometimes Ah is a more convenient unit than mAh.
The formula is:
Ah = Wh ÷ V
Then:
mAh = Ah × 1000
For example:
120 Wh ÷ 12 V = 10 Ah
10 Ah × 1,000 = 10,000 mAh
Therefore:
120 Wh at 12 V = 10 Ah = 10,000 mAh
How Battery Efficiency Changes Real Results
A mathematical conversion does not account for every real-world battery characteristic.
For example, a battery might contain a theoretical amount of energy, but the connected device cannot necessarily use all of it.
Losses can occur in:
- DC-DC converters
- Inverters
- Wiring
- Battery management systems
- Internal resistance
- Charging circuits
- Connectors
- Temperature effects
Therefore, calculated mAh should not automatically be interpreted as usable output capacity.
Common Questions
How many mAh are in 1 Wh?
There is no single answer because the result depends on voltage.
At 5 V:
1 × 1000 ÷ 5 = 200 mAh
At 3.7 V:
1 × 1000 ÷ 3.7 ≈ 270.27 mAh
How many mAh is 100 Wh?
It depends on voltage.
At 10 V:
10,000 mAh
At 20 V:
5,000 mAh
How many Wh is 10,000 mAh?
At 3.7 V:
10,000 × 3.7 ÷ 1000 = 37 Wh
At 5 V:
10,000 × 5 ÷ 1000 = 50 Wh
Can Wh and mAh be compared directly?
No. They are different measurements. Voltage must be considered.
Does a higher mAh rating always mean more energy?
No. A higher-voltage battery can contain more energy even with a lower mAh rating.
Does a higher Wh rating mean a battery lasts longer?
Generally, a higher Wh capacity means more stored energy, but runtime also depends on the device’s power consumption and system efficiency.
Conclusion
Converting watt-hours to milliamp-hours is easy once the relationship between energy, voltage, and charge is understood.
The key formula is:
mAh = (Wh × 1000) ÷ V
Always identify the appropriate voltage before performing the calculation.
The FREE TOOLS Watt-Hours to Milliamp-Hours Calculator can make this process faster when comparing batteries, power banks, solar storage systems, electronics, laptops, and other battery-powered equipment.
For accurate engineering decisions, always verify the manufacturer’s battery specifications and distinguish between nominal capacity and actual usable energy.
