Wh to mAh Calculator: Instantly Convert Battery Capacity

How to Use Our Wh to mAh Calculator

Our tool is designed for simplicity. You only need two pieces of information from your battery or device to get an accurate conversion.

• Watt-hours (Wh): This is a measure of a battery’s total energy capacity. Enter the watt-hour (Wh) rating of your battery. You can usually find this printed directly on the battery casing, the device itself, or in its technical specifications. For example, laptop batteries and portable power stations often use Wh.

• Voltage (V): This represents the battery’s electrical potential. Enter the nominal voltage (V) of the battery. This is a critical value for an accurate conversion and is almost always printed next to the Wh rating. Common voltages include 3.7V for smartphone batteries, 5V for USB power banks, and 11.1V, 14.8V, or higher for laptop and drone batteries.

Understanding Your Results: What is mAh?

The number our calculator provides is the battery’s capacity in milliampere-hours (mAh). But what does that actually mean?

Milliampere-hours (mAh) is a measure of electric charge. It tells you how much current a battery can provide over a specific amount of time. For example, a 5,000 mAh battery can theoretically provide 5,000 milliamps of current for one hour, or 1,000 milliamps for five hours. This is the most common unit used for consumer electronics like phones, headphones, and power banks.

The Formula Behind the Conversion

The relationship between energy (Wh), charge (mAh), and voltage (V) is straightforward. The calculator uses the following standard formula:

Why multiply by 1000? This step converts amps to milliamps (since 1 Amp = 1000 milliamps), giving you the familiar mAh value.

The key takeaway is that watt-hours is the most universal measure of capacity, as it accounts for both the charge (amps) and the voltage. A simple mAh rating alone doesn’t tell the whole story, which is why converting everything to a common unit is so important for a true comparison.

Why Voltage Matters: A Practical Example

Imagine you have two power banks, both advertised with different ratings.

• Power Bank A: 20,000 mAh (at a standard USB voltage of 5V)

• Power Bank B: 100 Wh

Which one has more capacity? Without converting, it’s impossible to know. Let’s use Power Bank B’s information. Assume it also operates at a standard 5V.

Using the formula: $(100\text{ Wh}\times 1000)/5\text{V}=20,000\text{ mAh}$

In this case, both power banks have the exact same energy capacity. The manufacturer of Power Bank B simply chose to use the more comprehensive “Wh” unit, which is also the standard used by airlines like the FAA for travel regulations.

The chart below shows how the same 100 Wh battery can have drastically different mAh ratings depending on its voltage.

This is why you can’t simply compare mAh values between two different types of batteries (like a phone battery and a laptop battery) without knowing their voltage.

Frequently Asked Questions About Battery Capacity

What is the real difference between Wh and mAh?

Think of it like this: mAh (milliampere-hours) is like the size of a gas tank (it measures charge/capacity). Wh (watt-hours) is like the total amount of energy in the gas (it measures energy). Wh is a more complete measure because it factors in the battery’s voltage. A large tank (high mAh) with low-energy fuel (low voltage) might provide less total power than a smaller tank (lower mAh) with high-energy fuel (high voltage).

Why do some batteries use Wh and others use mAh?

It mostly comes down to industry standards and application.

• mAh is consumer-friendly and has been used for small personal electronics (phones, headphones) for decades.

• Wh is technically a more accurate and universal unit of energy. It’s used for larger batteries (laptops, power stations) and is the official unit used by aviation authorities like the FAA and TSA for setting safety limits on batteries you can bring on a plane.

How do I find the voltage of my battery?

The voltage (V) is almost always printed directly on the battery’s label or casing. Look for a number followed by a “V”. You’ll typically find it near the other capacity information like Wh or mAh. If you can’t find it on the device, check the original packaging or the manufacturer’s official product page online under “Technical Specifications”. Be sure to use the “nominal voltage”, which is the standard operating voltage, not the maximum charging voltage.

Is a higher mAh rating always better?

Not necessarily. If you are comparing two identical types of batteries (e.g., two power banks that both output via standard 5V USB ports), then yes, the one with the higher mAh will last longer.

However, if you’re comparing batteries with different voltages (like a 3.7V phone battery vs. a 14.8V drone battery), the mAh value is misleading. The drone battery might have a lower mAh rating but contain significantly more total energy (Wh) because of its higher voltage. This is why converting to Wh is the best way to make a true comparison.

How many mAh is 100 Wh?

It completely depends on the voltage. As shown in the table above, 100 Wh is the maximum battery size allowed in carry-on luggage by the FAA without airline approval.

• At 3.7V (a phone battery), 100 Wh is 27,027 mAh.

• At 5V (a USB power bank), 100 Wh is 20,000 mAh.

• At 14.8V (a drone/laptop battery), 100 Wh is only 6,757 mAh.

Can I convert mAh to Wh?

Yes, you can easily do the reverse calculation. This is useful if your battery only shows an mAh rating and you want to know if it’s compliant with airline regulations.

The formula is:

Example: Your power bank is labeled “20,000 mAh” and uses a standard nominal voltage of 5V. $(20,000\text{ mAh}\times 5\text{V})/1000=100\text{ Wh}$. This is compliant with FAA rules.

What is “nominal voltage” and why is it important for this calculation?

A battery’s voltage isn’t perfectly constant; it fluctuates slightly as it discharges. The nominal voltage is the manufacturer’s stated, average voltage for the battery during operation. It’s the standard, “normal” voltage figure. You must use this nominal voltage for the Wh-to-mAh calculation to be accurate, not the “maximum” or “charging” voltage, which is often higher.

How does temperature affect battery capacity (mAh)?

Temperature has a significant impact.

• Cold temperatures slow down the chemical reactions inside a battery, which reduces its effective capacity and makes it drain faster. This is why your phone battery seems to die so quickly in the winter.

• Hot temperatures can increase performance temporarily but will degrade the battery’s long-term health and total lifespan much faster. For best results, keep batteries at room temperature.

Can I estimate my phone’s battery life from its mAh rating?

You can get a rough idea, but you can’t calculate exact hours. A phone’s battery life depends heavily on many factors besides the mAh rating:

• Screen brightness and resolution

• Processor workload (gaming vs. reading)

• Cellular signal strength (a weak signal uses more power)

• Background apps and notifications

• Software optimization

A 5,000 mAh battery will generally last longer than a 4,000 mAh battery in the same phone model, but you can’t compare it to a different phone with different hardware and software and expect the same results.

Does fast charging affect my battery’s mAh capacity over time?

Fast charging generates more heat than slow charging. Over time, excessive heat is the primary cause of battery degradation, which permanently reduces its maximum capacity (its effective mAh). While modern phones have systems to manage heat, consistently using the fastest charging method possible may lead to slightly faster capacity loss over the years compared to standard, slower charging.

Now that you’ve converted your battery’s Wh to mAh, you might want to see how that affects its runtime. Try our Battery Life Calculator to estimate how long your device will last. You can also do the reverse calculation with our mAh to Wh Calculator to check for airline compliance.