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Battery specifications can look complicated when different products use different units. A smartphone may advertise a battery in milliamp-hours, a laptop may use watt-hours, and a portable power station may use watt-hours or kilowatt-hours.
This can make battery comparisons difficult.
Fortunately, there is a simple mathematical relationship between these measurements.
A FREE TOOLS Milliamp-Hours to Watt-Hours Calculator can convert battery capacity from mAh to Wh when voltage is available.
The fundamental equation is:
Wh = mAh × V ÷ 1000
For example, a 6,000 mAh battery with a nominal voltage of 3.7 V has:
6,000 × 3.7 ÷ 1000 = 22.2 Wh
The calculator therefore reports approximately 22.2 Wh.
This article explains the science behind the conversion and shows how the calculation can be applied to everyday battery and electronics questions.
What Is Battery Capacity?
Battery capacity describes how much electrical charge a battery can store or deliver under specified conditions.
One common measurement is milliamp-hours.
For example:
2,000 mAh
5,000 mAh
10,000 mAh
The larger mAh number generally indicates greater charge capacity when comparing batteries of similar voltage, chemistry, and operating conditions.
However, mAh by itself does not completely describe battery energy.
Voltage must also be considered.
Why Battery Energy Is Different From Battery Capacity
The terms “capacity” and “energy” are sometimes used interchangeably in everyday conversation, but electrically they represent different concepts.
mAh describes charge.
Wh describes energy.
The relationship is:
Energy = Charge × Voltage
This means that two batteries with identical charge capacities can contain different amounts of energy if they have different voltages.
The Main Conversion Formula
To convert mAh into Wh:
Wh = (mAh × V) / 1000
For example:
12,000 mAh × 3.7 V ÷ 1000 = 44.4 Wh
Therefore, a 12,000 mAh battery at 3.7 V has approximately 44.4 Wh of nominal energy.
Why Divide by 1,000?
The reason is the prefix “milli.”
One milliamp is:
0.001 amp
Therefore:
1,000 mAh = 1 Ah
If you first convert mAh to Ah, the calculation becomes easier.
For example:
12,000 mAh = 12 Ah
Then:
12 Ah × 3.7 V = 44.4 Wh
Both approaches produce the same answer.
The Two-Step Method
Some users find the following method easier.
Step 1: Convert mAh to Ah
Ah = mAh ÷ 1000
For example:
8,000 mAh ÷ 1000 = 8 Ah
Step 2: Multiply by Voltage
Wh = Ah × V
If the battery voltage is 3.7 V:
8 × 3.7 = 29.6 Wh
Therefore:
8,000 mAh at 3.7 V = 29.6 Wh
Why an Online Calculator Is Convenient
Manual calculations are easy for one or two batteries.
But when comparing many products, an online calculator can be much faster.
A free mAh-to-Wh calculator can be useful when evaluating:
- Smartphones
- Tablets
- Laptops
- Power banks
- Rechargeable batteries
- Drones
- RC cars
- Cameras
- Portable speakers
- GPS devices
- Camping electronics
- Solar batteries
- Emergency power equipment
Users only need to enter the relevant values.
Practical Example: Smartphone Battery
Suppose a smartphone battery is:
4,800 mAh
with a nominal voltage of:
3.85 V
Calculate:
4,800 × 3.85 ÷ 1000 = 18.48 Wh
The nominal energy is approximately:
18.48 Wh
This value can help compare the battery with other devices.
However, it should not be used as a guarantee of how many hours the phone will operate.
Practical Example: Tablet Battery
Suppose a tablet battery has:
8,000 mAh
at:
3.8 V
Then:
8,000 × 3.8 ÷ 1000 = 30.4 Wh
The battery therefore has approximately 30.4 Wh of nominal energy.
Practical Example: Power Bank
Consider a power bank rated at:
20,000 mAh
Using a nominal cell voltage of:
3.7 V
gives:
20,000 × 3.7 ÷ 1000 = 74 Wh
The nominal stored energy is therefore about 74 Wh.
However, the power bank’s actual energy output can be lower.
Why Output Energy Can Be Lower
Power banks commonly need to convert their internal battery voltage to a different output voltage.
Every electronic conversion introduces some energy loss.
Other losses can occur because of:
- Internal resistance
- Heat
- Circuit efficiency
- Cable resistance
- Battery-management electronics
- Device charging efficiency
Consequently, 74 Wh of nominal battery energy does not mean that exactly 74 Wh will reach a connected smartphone.
Practical Example: Drone Battery
Suppose a drone battery is rated:
5,000 mAh
at:
22.2 V
Then:
5,000 × 22.2 ÷ 1000 = 111 Wh
The battery contains approximately 111 Wh of nominal energy.
If another battery has:
6,000 mAh at 14.8 V
its energy is:
6,000 × 14.8 ÷ 1000 = 88.8 Wh
Although the second battery has a higher mAh rating, it has less nominal energy.
This is a perfect example of why mAh should not be used alone for battery comparisons.
Practical Example: 12 V Battery
Suppose a battery is rated at:
7,000 mAh
and:
12 V
First convert:
7,000 mAh = 7 Ah
Then:
7 Ah × 12 V = 84 Wh
Therefore:
7,000 mAh at 12 V = 84 Wh
Practical Example: 24 V Battery
Suppose a battery pack has:
10,000 mAh at 24 V
Then:
10,000 × 24 ÷ 1000 = 240 Wh
Therefore:
10,000 mAh at 24 V = 240 Wh
Practical Example: 48 V Battery
A 48 V battery pack with:
20 Ah
contains nominally:
20 × 48 = 960 Wh
If its capacity is expressed in mAh:
20 Ah = 20,000 mAh
Therefore:
20,000 × 48 ÷ 1000 = 960 Wh
Comparing Batteries Fairly
Suppose you are comparing two batteries:
Battery A
10,000 mAh at 3.7 V
37 Wh
Battery B
8,000 mAh at 7.4 V
59.2 Wh
Battery B has lower mAh but greater energy.
This demonstrates an important principle:
Higher mAh does not necessarily mean higher energy.
For energy comparisons, Wh is often the more appropriate metric.
Estimating Runtime With Watt-Hours
Once battery energy is known, you can make a simple theoretical runtime estimate.
The formula is:
Runtime = Battery Wh ÷ Device Power W
Suppose a battery has:
100 Wh
and a device consumes:
20 W
Then:
100 ÷ 20 = 5 hours
The theoretical runtime is 5 hours.
In actual use, runtime can be shorter.
Why Runtime Estimates Are Not Exact
Several factors affect real-world battery runtime.
Device Power Changes
Many devices do not consume a constant amount of power.
A laptop may use very little power while idle but significantly more during gaming or video rendering.
Battery Efficiency
Not all stored energy is available to the device.
Temperature
Very high or very low temperatures can affect battery performance.
Battery Age
Battery capacity typically changes as batteries age.
Power Conversion
If the battery and device operate at different voltages, conversion electronics may be required.
Understanding Nominal Voltage
When performing an mAh-to-Wh calculation, users should generally use the appropriate nominal voltage rather than automatically using the maximum charging voltage.
For example, a lithium-ion cell can have a nominal voltage around 3.6–3.7 V while its fully charged voltage can be higher.
Using a maximum voltage instead of nominal voltage can produce a different energy estimate.
The correct value depends on what the calculation is intended to represent.
Battery Chemistry Matters
Different battery chemistries have different electrical characteristics.
Examples include:
- Lithium-ion
- Lithium-polymer
- Nickel-metal hydride
- Lead-acid
- Lithium iron phosphate
Their voltage characteristics, discharge curves, and energy density can differ.
Therefore, the calculator performs a mathematical conversion based on the values entered; it does not replace detailed battery specifications.
Understanding Battery Packs
A battery pack may contain multiple cells.
Cells can be connected:
- In series
- In parallel
- In series-parallel configurations
Series connections increase voltage.
Parallel connections increase capacity.
The resulting pack’s nominal energy can be calculated using:
Wh = Ah × V
provided the relevant pack voltage and capacity are known.
Series Battery Example
Suppose two identical cells each have:
3.7 V, 2,500 mAh
Connected in series:
Voltage becomes approximately:
7.4 V
Capacity remains:
2,500 mAh
Energy:
7.4 × 2.5 = 18.5 Wh
The two cells together therefore have approximately 18.5 Wh.
Parallel Battery Example
Two identical 3.7 V, 2,500 mAh cells connected in parallel produce approximately:
3.7 V, 5,000 mAh
Energy:
3.7 × 5 = 18.5 Wh
Again, the total nominal energy is approximately the sum of the individual cell energies.
Converting Wh to mAh
Sometimes you need to work in the opposite direction.
The formula is:
mAh = Wh × 1000 ÷ V
Suppose a battery is rated at:
60 Wh
and:
12 V
Then:
60 × 1000 ÷ 12 = 5,000 mAh
Therefore:
60 Wh at 12 V = 5,000 mAh
Converting Wh to Ah
The simpler formula is:
Ah = Wh ÷ V
For example:
120 Wh ÷ 12 V = 10 Ah
Therefore, a 12 V, 10 Ah battery is approximately 120 Wh.
Converting Wh to kWh
Large battery systems often use kilowatt-hours.
The conversion is:
kWh = Wh ÷ 1000
For example:
2,500 Wh ÷ 1000 = 2.5 kWh
This is common for larger battery storage systems and electric vehicles.
mAh to Wh Conversion Table
| mAh | Voltage | Wh |
|---|---|---|
| 1,000 | 3.7 V | 3.7 Wh |
| 2,000 | 3.7 V | 7.4 Wh |
| 3,000 | 3.7 V | 11.1 Wh |
| 4,000 | 3.7 V | 14.8 Wh |
| 5,000 | 3.7 V | 18.5 Wh |
| 6,000 | 3.7 V | 22.2 Wh |
| 8,000 | 3.7 V | 29.6 Wh |
| 10,000 | 3.7 V | 37 Wh |
| 15,000 | 3.7 V | 55.5 Wh |
| 20,000 | 3.7 V | 74 Wh |
| 30,000 | 3.7 V | 111 Wh |
How to Check Your Battery Voltage
Battery voltage can usually be found on:
- Battery labels
- Manufacturer specifications
- Product manuals
- Technical data sheets
- Battery-management software
- Device documentation
Do not assume that every battery with the same mAh rating uses the same voltage.
Can You Estimate Wh From mAh Alone?
Not accurately.
You can only calculate Wh if you know the voltage.
For example:
10,000 mAh
could represent:
- 37 Wh at 3.7 V
- 74 Wh at 7.4 V
- 120 Wh at 12 V
- 240 Wh at 24 V
Therefore, the voltage is essential.
What Does a Free mAh to Wh Calculator Do?
A calculator automates the mathematical process.
A typical tool requires:
Battery Capacity: mAh
Voltage: V
Then it calculates:
Energy: Wh
The calculator is especially useful for people who frequently compare batteries or work with electrical specifications.
Advantages for Students
Students studying:
- Physics
- Electronics
- Electrical engineering
- Renewable energy
- Applied mathematics
can use the calculator to verify manual calculations.
It can also help students understand the relationship between charge, voltage, power, and energy.
Advantages for Engineers and Technicians
Engineers and technicians may need to compare battery specifications across equipment.
A quick calculator can be useful for preliminary calculations and sanity checks.
For engineering designs, however, manufacturer specifications and detailed battery models should be used when precision is critical.
Advantages for Everyday Consumers
Consumers can use the calculator to better understand battery specifications before buying a product.
For example, someone comparing two power banks can calculate Wh rather than relying only on mAh.
This creates a more meaningful comparison when voltage differs.
Frequently Asked Questions
What is the formula for mAh to Wh?
The formula is:
Wh = mAh × V ÷ 1000
What information do I need?
You need the battery’s mAh capacity and voltage.
Can 10,000 mAh equal 100 Wh?
It can under a particular voltage. At 10 V, for example:
10,000 × 10 ÷ 1000 = 100 Wh
At 3.7 V, however, it is only 37 Wh.
How many Wh is 5,000 mAh?
It depends on voltage. At 3.7 V, it is 18.5 Wh.
Is a higher Wh battery always better?
Not necessarily. The appropriate battery depends on the device, voltage requirements, size, weight, discharge characteristics, and intended use.
Does mAh tell me battery runtime?
Not by itself. Runtime depends on voltage and the device’s power consumption.
Can the calculator determine actual battery life?
It can help estimate energy capacity, but actual runtime depends on real-world conditions.
Why does my calculated Wh differ from the manufacturer’s number?
Possible reasons include different nominal voltages, battery configurations, usable-energy limits, rounding, and differences in how the manufacturer defines capacity.
Tips for Accurate Battery Calculations
For better results:
- Check the manufacturer’s battery specifications.
- Identify the nominal voltage.
- Confirm the capacity is expressed in mAh.
- Use the formula correctly.
- Remember that 1,000 mAh equals 1 Ah.
- Use Wh when comparing energy between different voltage systems.
- Consider efficiency when estimating usable energy.
- Avoid treating nominal Wh as guaranteed runtime.
- Account for battery age in practical applications.
- Use detailed manufacturer data for critical engineering calculations.
Final Thoughts
A FREE TOOLS Milliamp-Hours to Watt-Hours Calculator is a convenient way to understand and compare battery energy.
The central formula is:
Wh = (mAh × V) ÷ 1000
The calculation is simple, but the concept is important.
mAh represents charge capacity. Wh represents energy. Voltage provides the connection between these measurements.
Whether you are comparing power banks, checking smartphone batteries, evaluating drone batteries, planning a solar project, working on an electronics project, or studying electrical concepts, converting mAh to Wh can provide a clearer picture of how much energy a battery can theoretically store.
For quick calculations, enter the battery capacity and voltage into a free online calculator and obtain the watt-hour result instantly.
Remember that the calculated value is normally a nominal energy estimate. Actual usable energy depends on battery chemistry, temperature, discharge conditions, conversion efficiency, battery age, and the specific equipment being powered.
Understanding these limitations allows you to use mAh-to-Wh calculations more effectively and make better battery and energy comparisons.
