How to Calculate mAh to Wh for Any Power Bank

Power bank labels can feel like they are speaking two different languages. One model shows 20,000mAh, while an airline asks for watt-hours. Another advertises 140W charging, which is a different measurement again. Once you understand the relationship between capacity, energy and voltage, the numbers become much easier to compare.

This guide explains mAh to Wh conversion in plain language. You will learn both formulas, see worked examples and understand why voltage changes the result. We will also look at usable capacity, charging speed and the UK rules for carrying power banks on flights. By the end, you should be able to read a battery label and work out what its figures mean in practice.

Quick Answer: The Wh to mAh Formula

To calculate Wh to mAh, multiply the watt-hours by 1,000 and divide by the battery's nominal voltage: mAh = (Wh × 1,000) ÷ V. For the reverse calculation, use Wh = (mAh × V) ÷ 1,000; either conversion requires the correct voltage.

Understanding Wh, mAh and Battery Voltage

Before reaching for a calculator, it helps to know what each figure describes. Wh, mAh and W are related, but they do not tell you the same thing.

What Watt-Hours Measure

Watt-hours measure stored energy. A 50Wh battery could theoretically supply 50W for one hour or 25W for two hours. Wh combines voltage and charge capacity, making it useful for comparing different batteries and applying aviation limits. Real runtime will be shorter because the system loses some energy.

What Milliamp-Hours Measure

Milliamp-hours measure electrical charge. mAh is commonly used to describe battery charge capacity in consumer electronics such as phones and power banks. However, two 10,000mAh batteries can store different amounts of energy if their nominal voltages differ.

Why Voltage Is Required for Conversion

Voltage connects electrical charge with energy. A 10,000mAh battery at 7.4V stores twice the energy of one at 3.7V. Check the nominal voltage on the power bank, packaging, manual or technical specifications before calculating.

Watts vs Watt-Hours

Watts describe the rate at which power moves, while watt-hours describe stored energy. A power bank can have a large Wh capacity but modest output, or smaller capacity with high output. Capacity affects potential runtime; watts affect charging speed.

How to Convert Wh to mAh

You may need this direction when a power bank shows Wh but you want to compare it with a device labelled in mAh. Keep the Wh and voltage figures from the same battery pack.

Wh to mAh Conversion Formula

Use this equation:

mAh = (Wh × 1,000) ÷ V

For example, a 37Wh battery at 3.7V gives:

(37 × 1,000) ÷ 3.7 = 10,000mAh

Always state the voltage beside a converted figure because using 5V or 12V would change the answer.

Step-by-Step Conversion Method

Follow these steps when the label provides Wh and nominal voltage:

1. Find the energy rating in Wh.
2. Find the nominal battery voltage in V.
3. Multiply the Wh value by 1,000.
4. Divide that result by the voltage.
5. Round only at the end.

Worked Wh to mAh Examples

Let's try a few realistic calculations:

• 18.5Wh at 3.7V: (18.5 × 1,000) ÷ 3.7 = 5,000mAh.
• 37Wh at 3.7V: (37 × 1,000) ÷ 3.7 = 10,000mAh.
• 74Wh at 3.7V: (74 × 1,000) ÷ 3.7 = 20,000mAh.
• 100Wh at 3.7V: (100 × 1,000) ÷ 3.7 ≈ 27,027mAh.

These results assume 3.7V. At 5V, 100Wh would equal 20,000mAh.

Wh to mAh Conversion Chart

The table below uses a nominal voltage of 3.7V. Treat it as a quick guide rather than a universal chart.

Watt-hours	Voltage	Approximate capacity
1Wh	3.7V	270mAh
5Wh	3.7V	1,351mAh
10Wh	3.7V	2,703mAh
20Wh	3.7V	5,405mAh
50Wh	3.7V	13,514mAh
100Wh	3.7V	27,027mAh
160Wh	3.7V	43,243mAh

How to Convert mAh to Wh

This direction is more useful for power bank owners in the UK. It lets you compare energy capacity across products and check the Wh category used for air travel.

mAh to Wh Conversion Formula

To convert mAh to Wh, use:

Wh = (mAh × V) ÷ 1,000

Suppose a battery is rated at 20,000mAh and 3.7V. Multiply 20,000 by 3.7, then divide by 1,000. The result is 74Wh.

If you need to convert mAh to watt hours, do not use the USB output voltage simply because the port says 5V or 9V. Use the nominal voltage associated with the rated mAh capacity.

Common Power Bank Capacity Examples

Here are common capacities calculated at 3.7V:

Rated capacity	Calculation	Energy
5,000mAh	5,000 × 3.7 ÷ 1,000	18.5Wh
10,000mAh	10,000 × 3.7 ÷ 1,000	37Wh
20,000mAh	20,000 × 3.7 ÷ 1,000	74Wh
25,000mAh	25,000 × 3.7 ÷ 1,000	92.5Wh

These examples do not replace the printed rating. Check the case because some power banks use another nominal voltage.

Choosing the Correct Voltage for Conversion

Most conversion errors come from choosing the wrong voltage, not from applying the formula incorrectly. The figures must describe the same side of the battery system.

Nominal Battery Voltage vs Output Voltage

Nominal voltage describes the battery cells or pack. USB output voltage describes what the power bank delivers after conversion. A unit may use cells around 3.6V to 3.8V yet offer several USB-C output profiles. Those outputs do not replace nominal voltage in the capacity formula.

Where to Find a Battery's Voltage

Start with the power bank label. Look for “battery capacity”, “nominal voltage” or Wh. If the case lacks detail, check the manual or product specifications. For flights, use the printed Wh figure when available and ask the manufacturer if the rating remains unclear.

Converting Multi-Cell Battery Capacities

Multi-cell packs can connect cells in series, parallel or both. Use the nominal voltage and mAh rating stated for the whole pack. Do not combine pack-level capacity with a single cell's voltage unless the specifications define both values that way.

Why Rated and Usable Battery Capacities Differ

The case shows stored capacity under specified conditions, not the energy that will reach another device.

Energy Loss During Power Conversion

Conversion circuitry, cables and batteries release some energy as heat. Wireless charging adds transfer losses, while alignment, case thickness and temperature also affect efficiency. A 10,000mAh power bank therefore will not deliver its full rated capacity to a phone battery.

Battery Capacity vs Charging Speed

Capacity and speed answer different questions. mAh and Wh describe available energy, while W indicates delivery rate. A 20,000mAh unit is not automatically faster than a 10,000mAh model. Check per-port output, combined output and device compatibility.

Factors Affecting Real-World Capacity

Real-world results vary with:

• Voltage-conversion efficiency
• Wired or wireless charging
• Cable quality and length
• Battery age and condition
• Surrounding temperature
• Background device activity
• Energy reserved by protective circuitry

Compare Wh where possible and allow for conversion losses.

UK Rules for Taking Power Banks on Flights

Wh matters to UK travellers because aviation guidance categorises lithium-ion batteries by stored energy. Your airline may apply conditions beyond the general thresholds.

Power Bank Capacity Limits

According to the UK Civil Aviation Authority (CAA), lithium-ion batteries under 100Wh are generally permitted in cabin baggage. Batteries between 100Wh and 160Wh require airline approval, while batteries above 160Wh are not permitted in passenger baggage. Keep the capacity rating visible.

Cabin Baggage and In-Flight Use

Power banks belong in cabin baggage rather than checked luggage. UK guidance currently permits two per person and says passengers should not recharge them onboard. Protect the terminals and keep each unit accessible. Some carriers also restrict using one to charge another device during the flight.

Checking Your Airline's Power Bank Policy

Check the carrier's baggage page before each journey. Policies can differ on quantity, onboard use and approval. Do not travel with a swollen, leaking, recalled, damaged or unusually hot battery. Remove power banks if cabin baggage is moved to the hold.

Choosing a Power Bank Using Wh, mAh and Watts

A useful power bank matches your devices and routine. Look beyond the largest capacity figure and consider how you will carry, recharge and use it.

Capacity for Daily Phone Charging

A 5,000mAh model suits emergency top-ups and commuting. A 10,000mAh option provides more energy for navigation, photography or streaming, with some additional size and weight.

Capacity for Travel and Multiple Devices

Around 20,000mAh suits longer periods away from a mains socket or several devices. Larger models can support laptops with suitable USB-C output. Before flying, check the printed Wh rating. Higher capacity also takes longer to refill unless the power bank accepts a strong input.

Output Requirements for Phones, Tablets and Laptops

Check the power your device accepts. Phones may need modest USB-C output, while laptops often require 45W, 65W or more. Combined output matters for several devices; single-port output matters for one laptop.

Ports, Cables and Wireless Charging

Choose ports that suit your cables. USB-C often handles input and output, while USB-A serves older accessories. Built-in cables reduce packing, and magnetic charging adds convenience. For efficiency or multi-device use, check wired options and how power is divided across active ports.

Portability, Recharging and Flight Suitability

Compare dimensions, weight and maximum input alongside capacity. Compact models suit daily carry; larger ones better support laptops and longer trips. For flights, look for a clear Wh label and confirm the airline's policy before packing.

Anker Power Banks for Different Charging Needs

Anker power banks cover compact magnetic chargers, travel-friendly multi-device models and higher-output options for laptops. The right choice depends on what you charge and how much weight you want to carry.

Anker Nano Power Bank, 5,000mAh for Lightweight Everyday Charging

The Anker Nano Power Bank, 5,000mAh is designed for users who need quick phone top-ups without carrying extra weight. Its slim magnetic design makes it easy to attach to compatible iPhones while travelling or commuting.

• 5,000mAh capacity for everyday backup charging.
• Up to 15W Qi2-compatible magnetic charging.
• 20W two-way USB-C charging for wired output and recharging.
• Ultra-slim 0.3-inch design for pocket-friendly portability.

It is best suited for smartphone users who prioritise convenience and portability over multiple full device charges.

Anker MagGo Power Bank (10K, 35W) for Apple Users and Travel

The Anker MagGo Power Bank (10K, 35W) is built for Apple users who want to charge multiple devices with fewer accessories. Its integrated USB-C cable and Apple Watch charging module make it a practical option for travel and daily carry.

• 10,000mAh capacity for extended mobile charging.
• Built-in USB-C cable for convenient connection.
• Up to 30W USB-C charging output.
• Up to 5W Apple Watch charging.
• Apple-certified charging support for compatible Apple Watch models.

It suits iPhone and Apple Watch users who want an all-in-one charging solution for trips and busy days.

Anker Prime Power Bank (20K, 220W) for Mobile Workstations

The Anker Prime Power Bank (20K, 220W) is designed for professionals who need reliable power for laptops, tablets and smartphones while working remotely. With high output capacity and fast recharge support, it provides a stronger alternative to compact travel power banks.

• 20,100mAh capacity (72.36Wh).
• Up to 220W total output across multiple ports.
• Up to 140W charging from a single USB-C port.
• Up to 100W USB-C input for faster recharging.
• Smart display for charging status monitoring.

It is ideal for business travellers, creators and laptop users who need high-performance charging on the move.

Anker Prime Power Bank (26K, 300W) for High-Performance Charging

The Anker Prime Power Bank (26K, 300W) delivers the highest output in the lineup, targeting users who carry multiple power-hungry devices. It combines a large battery capacity with fast charging speeds for demanding mobile setups.

• 26,250mAh capacity (99.75Wh).
• Up to 300W total output.
• Up to 140W charging from a single USB-C port.
• Up to 250W dual USB-C recharging.
• Smart display and app control for power management.

It is best suited for professionals, content creators and frequent travellers who need maximum charging capacity rather than the smallest possible size.

Common Wh and mAh Conversion Mistakes

• Converting without knowing the voltage: At 3.7V, 100Wh is about 27,027mAh; at 5V, it is 20,000mAh. Find the voltage before calculating.
• Using output voltage instead of nominal voltage: USB-C output can change as a device negotiates different power profiles. The battery's rated mAh usually relates to its cells or pack, so pair it with the matching nominal voltage rather than a convenient output figure.
• Confusing capacity with charging speed: A large mAh figure does not guarantee faster charging. Capacity, output and device compatibility all matter. Check W for speed and Wh or mAh with voltage for stored capacity.
• Assuming rated capacity equals delivered capacity: Conversion, cables, heat and wireless transfer consume energy. Treat the case rating as stored capacity, not the capacity delivered to another battery.

Conclusion

Once you can read a power bank label, mAh to Wh conversion becomes a useful decision tool rather than just a maths exercise. It helps you judge whether a battery suits your travel plans, compare models that use different labels and separate capacity from charging speed.

The most important habit is to match the mAh figure with its correct nominal voltage. Use the printed Wh rating when one is available, especially before a UK flight, and check the carrier's current conditions. When choosing a power bank, balance energy capacity with output, port selection, recharge time and weight. That approach leads to a charger that fits your routine instead of simply having the biggest number on the box.

FAQs

How many mAh is 100Wh?

At 3.7V, 100Wh equals approximately 27,027mAh. However, there is no single result because voltage changes the conversion. The same 100Wh equals 20,000mAh at 5V and about 8,333mAh at 12V. Use mAh = (Wh × 1,000) ÷ V and match the voltage to the battery's rated capacity before using the answer.

Can you convert Wh to mAh without voltage?

No. Watt-hours measure energy, while milliamp-hours measure electrical charge. Voltage connects the two units, so leaving it out makes an accurate conversion impossible. Once you know the battery's nominal voltage, use mAh = (Wh × 1,000) ÷ V. Check the label, manual or product specifications before calculating the final capacity figure.

How many Wh is a 10,000mAh power bank?

A 10,000mAh power bank stores 37Wh when its nominal voltage is 3.7V. Use Wh = (mAh × V) ÷ 1,000: 10,000 × 3.7V ÷ 1,000 = 37Wh. However, 37Wh is not universal because some battery packs use another nominal voltage. Check the Wh value printed on the case when available.

How many Wh is a 20,000mAh power bank?

A 20,000mAh power bank equals 74Wh when rated at 3.7V. Calculate it with Wh = (mAh × V) ÷ 1,000: 20,000 × 3.7 ÷ 1,000 = 74Wh. Because power banks can use different internal designs and nominal voltages, confirm the voltage or printed Wh rating before using this figure for travel or product comparisons.

Can I take a 20,000mAh power bank on a UK flight?

Yes. A 20,000mAh power bank rated at 3.7V stores about 74Wh, placing it below the usual 100Wh threshold. Current UK flight guidance requires power banks to stay in cabin baggage, limits passengers to two and says they should not be recharged onboard. Check your airline's policy before travelling.