nicole nielsen
Battery capacity can be described in several different ways. Depending on the product, you may see mAh, Ah, Wh, or kWh printed on the specification label.
Understanding these units is especially important when comparing batteries with different voltages.
A Watt-Hours to Milliamp-Hours Calculator provides a convenient way to translate an energy rating in Wh into an equivalent mAh value when the voltage is known.
This guide explains battery capacity, the Wh-to-mAh formula, examples, applications, limitations, and practical ways to compare batteries.
What Is Battery Capacity?
Battery capacity describes how much electrical charge or energy a battery can store.
Two common measurements are:
- Milliamp-hours (mAh)
- Watt-hours (Wh)
These units are related but should not be treated as identical.
mAh Measures Charge
Milliamp-hours indicate electrical charge capacity.
Wh Measures Energy
Watt-hours indicate stored energy.
Because energy depends on both charge and voltage, Wh provides a more complete way to compare batteries operating at different voltages.
The Basic Electrical Relationship
The relationship can be written as:
Energy = Voltage × Charge
Using standard battery units:
Wh = V × Ah
Because:
1 Ah = 1,000 mAh
we can derive:
Wh = V × mAh ÷ 1,000
Solving for mAh:
mAh = Wh × 1,000 ÷ V
This is the central formula for the calculator.
How the Calculator Works
A typical free Watt-Hours to Milliamp-Hours Calculator requires two inputs:
- Watt-hours
- Voltage
The calculator then applies:
mAh = (Wh × 1000) / Voltage
For example:
Wh = 60
Voltage = 12 V
Calculation:
60 × 1000 ÷ 12
= 5,000 mAh
Why You Need Voltage
Consider two batteries that both have 50 Wh.
The first operates at 5 V:
50 × 1000 ÷ 5 = 10,000 mAh
The second operates at 10 V:
50 × 1000 ÷ 10 = 5,000 mAh
They contain the same amount of energy according to the 50 Wh rating, but their mAh values are different.
Therefore, saying “50 Wh equals 10,000 mAh” without specifying voltage is incomplete.
Battery Capacity Comparison
Suppose you are comparing:
Battery A
10,000 mAh at 3.7 V
Energy:
10,000 × 3.7 ÷ 1000 = 37 Wh
Battery B
8,000 mAh at 5 V
Energy:
8,000 × 5 ÷ 1000 = 40 Wh
Battery B has fewer milliamp-hours but slightly more watt-hours.
This is an important reason to compare Wh when batteries have different operating voltages.
Understanding Ah
Amp-hours are closely related to milliamp-hours.
The conversion is:
Ah = mAh ÷ 1000
and:
mAh = Ah × 1000
For example:
7 Ah = 7,000 mAh
15 Ah = 15,000 mAh
25 Ah = 25,000 mAh
For larger battery systems, Ah is generally easier to read than mAh.
Understanding kWh
For very large battery systems, energy is often expressed in kilowatt-hours.
The relationship is:
1 kWh = 1,000 Wh
For example:
3 kWh = 3,000 Wh
If a 3 kWh battery operates at 48 V:
3,000 × 1,000 ÷ 48
≈ 62,500 mAh
That is:
62.5 Ah
This illustrates why large battery systems normally use Ah and kWh rather than mAh.
Wh to mAh for Portable Electronics
Portable electronics are among the most common applications for this conversion.
Examples include:
- Smartphones
- Tablets
- Laptops
- Cameras
- Handheld gaming devices
- Portable monitors
- Bluetooth speakers
- GPS devices
- Wireless routers
- Portable projectors
Manufacturers may use different battery specifications, making unit conversion useful when comparing products.
Wh to mAh for USB Devices
USB devices often operate at approximately 5 V at the input, but internal battery voltage can differ.
If a device requires 25 Wh at 5 V:
25 × 1000 ÷ 5 = 5,000 mAh
However, if the 25 Wh figure describes internal battery energy at another voltage, use that battery voltage instead.
This distinction is important when analyzing power banks and USB battery systems.
Power Bank Example
Suppose a power bank contains an internal lithium battery rated approximately:
20,000 mAh at 3.7 V
Its energy is:
20,000 × 3.7 ÷ 1000
= 74 Wh
If you incorrectly use the 5 V USB output voltage to calculate the internal mAh rating, you may get a different result.
The correct voltage depends on what the specification represents.
Laptop Battery Example
Suppose a laptop battery is rated:
80 Wh
with a nominal voltage of:
15.2 V
Then:
80 × 1000 ÷ 15.2
≈ 5,263 mAh
The result is an approximate equivalent based on the stated nominal voltage.
Solar Battery Example
Suppose a 12 V battery is rated at:
240 Wh
The corresponding charge capacity is:
240 × 1000 ÷ 12
= 20,000 mAh
or:
20 Ah
This can help when comparing energy-based specifications with Ah-based battery specifications.
Battery Runtime and Wh
One major advantage of Wh is that it can be used more directly to estimate runtime.
A simplified formula is:
Runtime in hours = Battery Energy in Wh ÷ Device Power in W
For example, a 100 Wh battery powering a 20 W device:
100 ÷ 20 = 5 hours
This is an idealized estimate.
Actual runtime may be lower because of efficiency losses and battery characteristics.
Why Actual Runtime May Be Lower
A battery rated at 100 Wh does not necessarily provide 100 Wh of usable energy to the device.
Potential losses include:
- Voltage conversion
- Inverter losses
- Battery management
- Heat
- Internal resistance
- Wiring resistance
- Aging
- High discharge rates
- Low temperatures
- Device power fluctuations
If a system is 90% efficient, for example, a simplified usable-energy estimate would be:
100 Wh × 0.90 = 90 Wh
A 20 W device would then theoretically operate for:
90 ÷ 20 = 4.5 hours
Real results can still vary.
Battery Chemistry Matters
Different battery chemistries behave differently.
Common rechargeable battery types include:
- Lithium-ion
- Lithium-polymer
- LiFePO4
- Nickel-metal hydride
- Lead-acid
Their voltage characteristics, discharge behavior, energy density, and usable capacity differ.
Therefore, a mathematical conversion should not be interpreted as a complete battery-performance analysis.
Nominal Voltage vs Actual Voltage
Battery voltage can change while the battery discharges.
For example, a battery may have a nominal voltage used for capacity calculations even though its actual voltage is higher when fully charged and lower near depletion.
When converting Wh to mAh, the voltage specified by the battery manufacturer should be preferred.
Wh to mAh Formula in Different Situations
10 Wh at 3.7 V
10 × 1000 ÷ 3.7
≈ 2,703 mAh
20 Wh at 3.7 V
20 × 1000 ÷ 3.7
≈ 5,405 mAh
30 Wh at 5 V
30 × 1000 ÷ 5
= 6,000 mAh
50 Wh at 10 V
50 × 1000 ÷ 10
= 5,000 mAh
100 Wh at 12 V
100 × 1000 ÷ 12
≈ 8,333 mAh
500 Wh at 24 V
500 × 1000 ÷ 24
≈ 20,833 mAh
Quick Conversion Table
| Wh | 3.7 V | 5 V | 12 V | 24 V |
|---|---|---|---|---|
| 10 Wh | 2,703 mAh | 2,000 mAh | 833 mAh | 417 mAh |
| 20 Wh | 5,405 mAh | 4,000 mAh | 1,667 mAh | 833 mAh |
| 50 Wh | 13,514 mAh | 10,000 mAh | 4,167 mAh | 2,083 mAh |
| 100 Wh | 27,027 mAh | 20,000 mAh | 8,333 mAh | 4,167 mAh |
| 200 Wh | 54,054 mAh | 40,000 mAh | 16,667 mAh | 8,333 mAh |
How to Use a FREE Wh to mAh Calculator
A free online calculator can simplify battery conversions.
Enter the Energy
Input the battery’s Wh rating.
Enter Voltage
Input the relevant voltage.
Calculate
The calculator applies:
Wh × 1000 ÷ V
Check the Result
The result is displayed in milliamp-hours.
Always check whether the voltage you entered corresponds to the battery rating.
Who Uses a Wh to mAh Calculator?
This tool can be useful for:
- Electronics students
- Electrical engineers
- DIY hobbyists
- Solar installers
- Battery enthusiasts
- Robotics builders
- Drone users
- Power-bank users
- Laptop users
- Portable-device owners
- Renewable-energy enthusiasts
- Makers
- Technicians
Educational Applications
Students learning electricity can use Wh-to-mAh conversion to understand the relationship between:
- Voltage
- Current
- Charge
- Power
- Energy
- Battery capacity
For example, students can calculate how changing voltage affects the mAh equivalent of a fixed energy value.
Engineering Applications
Engineers may need to convert specifications when selecting components or comparing batteries.
A manufacturer may provide energy capacity in Wh, while another battery supplier provides capacity in Ah.
The conversion allows both specifications to be evaluated using a common electrical framework.
Common Errors When Converting Wh to mAh
Using 1,000 Without Voltage
Some people assume:
1 Wh = 1,000 mAh.
This is incorrect.
Confusing W and Wh
Watts measure power.
Watt-hours measure energy.
They are not interchangeable.
Confusing A and Ah
Amps measure current.
Amp-hours measure charge capacity.
Using Output Voltage Instead of Battery Voltage
When dealing with power banks or converters, distinguish between the battery’s internal voltage and the output voltage.
Assuming Calculated mAh Is Guaranteed Usable Capacity
The mathematical result does not automatically account for efficiency or battery losses.
Frequently Asked Questions
What is the formula for Wh to mAh?
The formula is:
mAh = (Wh × 1000) ÷ V
Can I convert 1 Wh to mAh?
Yes, but you must know the voltage.
At 5 V:
1 Wh = 200 mAh
At 3.7 V:
1 Wh ≈ 270.27 mAh
Is 5,000 mAh always equal to the same Wh?
No. The Wh value depends on voltage.
At 3.7 V:
5,000 × 3.7 ÷ 1000 = 18.5 Wh
At 5 V:
5,000 × 5 ÷ 1000 = 25 Wh
Which is more important, Wh or mAh?
It depends on the application. Wh is useful for comparing energy across different voltages, while mAh is commonly used for batteries and portable electronics.
How do I convert mAh into Wh?
Use:
Wh = mAh × V ÷ 1000
Can the calculator be used for rechargeable batteries?
Yes. Use the appropriate nominal voltage and battery capacity information.
Does higher voltage increase mAh?
For a fixed Wh value, increasing voltage actually decreases the calculated mAh value because:
mAh = Wh × 1000 ÷ V
Can I calculate battery runtime with Wh?
Yes, approximately:
Runtime = Wh ÷ Watts
But real runtime depends on efficiency and operating conditions.
Final Conclusion
The Watt-Hours to Milliamp-Hours Calculator is a useful tool for converting battery energy specifications into an equivalent milliamp-hour rating.
The fundamental relationship is:
mAh = (Wh × 1000) ÷ V
The most important variable is voltage. Without voltage, there is no single mAh equivalent for a given Wh value.
Whether you are working with a smartphone, power bank, laptop, solar battery, robotics project, portable electronics, or larger energy-storage system, understanding Wh and mAh helps you compare battery specifications more accurately.
Use the FREE TOOLS Watt-Hours to Milliamp-Hours Calculator whenever you need a quick conversion, but remember that calculated capacity is not necessarily the same as usable real-world capacity. For important electrical or battery-system decisions, verify the manufacturer’s specifications, nominal voltage, battery chemistry, and efficiency requirements.
