mAh to Wh Converter for Airline Travel (FAA/TSA Compliant)

How to Use Our mAh to Wh Converter

To find the watt-hours of your battery, you only need two pieces of information. Both are usually printed directly on the battery or device casing.

• Battery Capacity (in mAh): Enter the capacity of your battery in milliamp-hours. This is often a large number, like 10,000mAh or 20,000mAh on power banks.

• Voltage (in Volts): Enter the nominal voltage (V) of your battery. For most USB power banks and phone batteries, this is 3.7V. For laptop batteries, it’s often 11.1V or 14.8V.

Once you enter both values, the calculator will instantly provide the capacity in Watt-hours (Wh).

Understanding Your Results

The result from the calculator is your battery’s capacity in Watt-hours (Wh). This number is the most important measure of the total amount of energy stored in a battery. Here’s a breakdown of what makes up this calculation.

• Milliamp-hour (mAh): Think of mAh as the size of the fuel tank. It measures charge and tells you how much current a battery can provide for a certain amount of time. While a bigger number is often better, it doesn’t tell the whole story.

• Voltage (V): Think of voltage as the pressure or power of that fuel. It’s the electrical force that pushes the energy out of the battery.

• Watt-hour (Wh): This is the true measure of total energy. It’s the combination of the fuel tank’s size (mAh) and the fuel’s pressure (V). It answers the question, “How much work can this battery actually do?”

The formula used by the calculator is:

We divide by 1,000 to convert from milliamp-hours to the standard amp-hours used in the watt-hour formula.

Why Watt-Hours are a Better Measure

Comparing two batteries by mAh alone can be misleading if they have different voltages.

As you can see, the laptop and smartphone batteries both have a 5,000 mAh capacity, but the laptop battery contains three times more energy because its voltage is higher. This is why airlines use Watt-hours for their limits.

Frequently Asked Questions

Why do airlines have a 100 Wh limit for batteries?

Safety is the primary reason. Lithium-ion batteries, which are used in most power banks and electronics, store a lot of energy in a small space. If they are damaged, they can short-circuit and enter “thermal runaway,” leading to an intense fire that is difficult to extinguish.

By limiting batteries to 100 Wh, airlines and aviation authorities like the FAA and TSA establish a reasonable safety threshold for what can be carried in the cabin without special permission. This amount of energy is sufficient for most personal electronics while limiting the potential danger if a battery were to fail during a flight. Batteries must be in your carry-on luggage, not in checked bags.

Can I bring a battery over 100 Wh on a plane?

Yes, but with restrictions. According to the FAA:

• Batteries up to 100 Wh: Allowed in carry-on luggage without limit.

• Batteries between 101 Wh and 160 Wh: You can bring up to two of these larger batteries in your carry-on luggage, but you must get airline approval first.

• Batteries over 160 Wh: Forbidden on passenger aircraft.

Always check with your specific airline before you fly.

Is a 20,000 mAh power bank always better than a 10,000 mAh one?

Assuming they have the same voltage (typically 3.7V for USB power banks), then yes. A 20,000 mAh power bank holds twice the charge and therefore roughly twice the energy of a 10,000 mAh one.

• 10,000 mAh @ 3.7V = 37 Wh

• 20,000 mAh @ 3.7V = 74 Wh

The 20,000 mAh power bank can charge your phone more times before it needs to be recharged itself. Both are under the 100 Wh airline limit.

How can I find my battery’s voltage if it’s not printed?

Finding the voltage is key for an accurate conversion. Here are a few places to look:

1. On the Battery/Device: It’s almost always printed on the device casing or the battery itself, often near the mAh rating. Look for a number followed by a “V”.

2. Product Manual: The technical specifications section of the product manual will list the nominal voltage.

3. Manufacturer’s Website: Check the product page or support section online for your device’s model number.

4. Standard Voltages: As a rule of thumb:

   • Most single-cell lithium-ion batteries (phones, power banks, vapes) are 3.7V.

   • Laptop batteries are typically 11.1V or 14.8V.

   • Car batteries are 12V.

Why doesn’t my 20,000 mAh power bank charge my 5,000 mAh phone four times?

This is a great question that comes down to two factors: voltage conversion and efficiency loss.

1. Voltage Mismatch: Your 20,000 mAh power bank is rated at 3.7V, but it has to boost that voltage to 5V to send power over a USB cable. This conversion consumes energy.

2. Efficiency Loss: No energy transfer is 100% efficient. Energy is lost as heat in the power bank’s circuitry, the charging cable, and your phone’s battery. A realistic efficiency is around 80-90%.

Because of these losses, a 20,000 mAh power bank might only deliver the equivalent of 14,000 mAh to your phone, giving you closer to 2.5-3 charges instead of a perfect 4.

What does the “nominal voltage” of a battery mean?

“Nominal voltage” is the standard, “named” voltage of a battery. In reality, a battery’s voltage changes as it charges and discharges. For example, a 3.7V lithium-ion battery might be at 4.2V when fully charged and drop to 3.0V when empty. The nominal voltage (3.7V) is the average or typical voltage for its operating range.

How do I calculate how long my battery will last?

You can estimate this if you know the power consumption of the device it’s running. The formula is: Time (hours) = Battery Watt-hours (Wh) / Device Power (Watts)

Concrete Example: You have a 74 Wh power bank and you want to power a small fan that consumes 5 Watts. Time = 74 Wh / 5 W = 14.8 hours Factoring in efficiency losses (~85%), a more realistic estimate would be 14.8 hours * 0.85 = 12.5 hours.

What’s the difference between Wh and kWh?

kWh stands for kilowatt-hour. The prefix “kilo-” simply means 1,000.

• 1 kWh = 1,000 Wh

Watt-hours (Wh) are used for smaller batteries in consumer electronics. Kilowatt-hours (kWh) are used for very large batteries (like in an electric vehicle) and for measuring household electricity consumption on your utility bill.

Can I bring multiple batteries on a plane?

Yes. The FAA limit is per battery. You can carry multiple batteries as long as each individual battery is at or below the 100 Wh limit. For example, you could bring four separate 74 Wh (20,000 mAh) power banks without issue.

Why do some power banks list two different mAh ratings?

You might see a power bank advertised with “20,000 mAh (Cell Capacity)” and a smaller “13,000 mAh (Rated/Output Capacity)”.

• Cell Capacity (e.g., 20,000 mAh @ 3.7V): This is the total capacity of the raw lithium-ion cells inside the power bank.

• Rated/Output Capacity (e.g., 13,000 mAh @ 5V): This is the realistic amount of charge the power bank can actually deliver to your device over a 5V USB connection after accounting for the energy lost during the voltage conversion from 3.7V to 5V. This is the more honest and useful number.

Now that you understand your battery’s true energy capacity, you might want to estimate how long it will power a specific device. Check out our Battery Life Calculator to do just that. If you’re working with other electrical units, our Ohm’s Law Calculator can help you understand the relationship between voltage, current, and resistance.