mAh to Wh: Formula, Calculator, and Battery Energy Examples

Shopping for rechargeable gear often feels like reading two entirely different languages. On one shelf, handheld power banks, smartphone cells, and camera packs advertise massive numbers like 10,000mAh, 20,000mAh, or 26,800mAh. On the next shelf, electric bikes, camping battery packs, and laptops list their storage in modest two- or three-digit numbers like 65Wh, 99Wh, or 288Wh.

At first glance, a 20,000mAh pocket charger sounds vastly larger than a 100Wh laptop battery. In physical reality, the 100Wh battery stores significantly more total energy.

Bridging that mental gap requires converting mAh to Wh.

Because milliamp-hours measure the amount of electric charge moving through a circuit while watt-hours measure the actual work that charge can perform, you cannot convert between them without factoring in electrical pressure, nominal voltage. Knowing this conversion helps you compare battery energy, estimate runtime alongside device load and efficiency, and check airline carry-on restrictions before traveling.

mAh vs. Wh: How These Battery Capacity Metrics Differ

Comparing battery sizes without checking voltage is like comparing fuel tanks using only the height of the container without knowing its diameter or pressure.

• Charge Capacity (mAh / Ah): The amount of electric charge a battery can deliver under specified discharge conditions.

• Electrical Potential (Volts): The electrical pressure pushing those electrons through the circuit.

• Energy Capacity (Wh / kWh): The actual physical work the stored electricity can perform over time.

Milliamp-Hours Measure Electric Charge

A milliamp-hour (mAh) is one-thousandth of an amp-hour (1 Ah = 1,000 mAh). It represents electrical charge capacity: current multiplied by time, measured under specified discharge conditions, rather than a guarantee of how much current the battery can deliver.

For instance, as theoretical charge arithmetic, 5,000mAh is equivalent to 5,000 milliamps (5 Amps) for one hour or 500 milliamps for 10 hours; actual discharge current and runtime depend on the battery's ratings and operating conditions.

However, charge capacity alone tells you nothing about how much heat, light, or mechanical computing work those electrons can accomplish. A small 1.2V nickel-metal hydride (NiMH) AA rechargeable cell and a high-voltage lithium drone cell might both carry a "2,500mAh" label, but the drone battery stores substantially more energy because its higher nominal voltage yields more watt-hours at the same mAh rating; maximum output power also depends on the battery's discharge-current capability.

Watt-Hours Measure Actual Stored Energy

A watt-hour (Wh) represents true electrical energy. One watt-hour equals one watt of sustained power delivered over one full hour (or 3,600 Joules of energy).

Because energy takes both current and voltage into account (Watts = Volts * Amps), watt-hours provide an absolute, apples-to-apples baseline. A 100Wh battery stores the same fundamental energy reserve whether it is configured as a low-voltage phone pack, a 12V marine battery, or an 18V power tool brick.

This universal measurement is why electrical engineers, safety regulators, and aviation authorities rely on watt-hours rather than milliamp-hours to govern battery safety and system design.

The Exact Formula for Converting Milliamp-Hours to Watt-Hours

To convert milliamp-hours into watt-hours, multiply the battery's capacity in amp-hours by its nominal voltage. Because 1 amp-hour equals 1,000 milliamp-hours, divide the mAh rating by 1,000 before multiplying by voltage. The Federal Aviation Administration's battery guidance uses this same method for calculating watt-hours.

The Conversion Formula

• Watt-Hours = (Milliamp-Hours × Nominal Voltage) / 1,000
• In short notation: Wh = (mAh × V) / 1,000
• Or, when working directly in Amp-Hours: Wh = Ah × V

Worked Step-by-Step Examples Across Different Chemistries

Standard 10,000mAh Pocket Power Bank

• Stated Charge: 10,000mAh
• Internal Nominal Voltage: 3.7V (typical nominal voltage for a single lithium-ion cell)
• Calculation: (10,000 × 3.7) / 1,000 = 37,000 / 1,000
• Result: 37 Watt-Hours (Wh)

High-Capacity 26,800mAh Travel Charger

• Stated Charge: 26,800mAh
• Internal Nominal Voltage: 3.7V
• Calculation: (26,800 × 3.7) / 1,000 = 99,160 / 1,000
• Result: 99.16 Watt-Hours (Wh)

This places the calculated capacity just below the commonly applicable 100Wh threshold for lithium batteries on passenger aircraft. The FAA states that rechargeable batteries up to 100Wh are generally permitted, while batteries from 101–160Wh require airline approval. Airline-specific restrictions may also apply.

12.8V LiFePO4 Auxiliary Battery Pack

• Stated Charge: 20,000mAh (20Ah)
• Internal Nominal Voltage: 12.8V (a typical nominal voltage for a four-cell LiFePO4 battery connected in series)
• Calculation: (20,000 × 12.8) / 1,000 = 256,000 / 1,000
• Result: 256 Watt-Hours (Wh)

The key distinction is that milliamp-hours alone do not tell you how much energy a battery stores. A 20,000mAh battery rated at 3.7V has a nominal energy value of 74Wh, while a 20,000mAh LiFePO4 battery rated at 12.8V has a nominal energy value of 256Wh. The second battery therefore has more than three times the nominal energy despite having the same mAh rating.

Converting Watt-Hours Back to Milliamp-Hours: Step-by-Step

When an airline regulation, safety standard, or hardware manual specifies a battery in watt-hours, you may want to reverse the equation to find out how many milliamp-hours that equates to for your specific device.

The Reverse Formula

• Milliamp-Hours = (Watt-Hours * 1,000) / Nominal Voltage
• In short notation: mAh = (Wh * 1,000) / V
• Or, for Amp-Hours: Ah = Wh / V

To see why knowing the voltage is non-negotiable, examine how the universal 100Wh airline carry-on limit translates across different battery architectures:

As shown above, asking "How many mAh is 100Wh?" has five completely different answers depending on the internal voltage of the battery.

Quick Reference: mAh to Wh Lookup Across Common Batteries

The following lookup table maps standard consumer battery sizes to their calculated watt-hour ratings using illustrative battery configurations and assumed nominal voltages:

Calculations based on illustrative battery configurations and assumed nominal voltages, not manufacturer-certified ratings for specific devices. Always inspect the physical label printed on your device casing for manufacturer-certified Wh ratings.

The 3.7V vs. 5V Trap: Why Nominal Voltage Matters

The single most frequent mistake people make when calculating mAh to Wh is using the USB output voltage instead of the internal battery voltage.

When you look at a USB power bank, the ports on the outside are labeled 5V (standard USB-A), 9V, 12V, 15V, or 20V (USB-C Power Delivery). However, the chemical cells sealed inside that plastic enclosure almost universally operate at a nominal 3.6V to 3.85V:

1. Internal Battery Storage (3.7V Chemical Nominal): The raw chemical cells hold energy at roughly 3.7 Volts. The printed mAh rating on the shell describes capacity at this internal level.

2. Internal DC-to-DC Boost Circuitry: Electronics convert that native 3.7V power up to higher voltages like 5V or 9V to feed external devices.

3. USB Port Output (5V / 9V / 20V): The delivered voltage is negotiated by your phone or laptop.

If you take a 20,000mAh charger and multiply it by 5V:

• Incorrect: (20,000 * 5.0V) / 1,000 = 100Wh

If an airport security officer applied that 5V math, they might flag your power bank as bordering on the legal limit. But when calculated using the true internal 3.7V cell rating:

• Correct: (20,000 * 3.7V) / 1,000 = 74Wh

The battery holds 74Wh of actual energy. When that internal battery feeds power to your phone via USB-C, an internal step-up (boost) converter elevates the voltage to 5V or 9V while stepping down the usable output current accordingly. Always look for the fine print on the manufacturer's specification plate: quality electronics print the internal voltage (e.g., "3.7V / 74Wh") directly on the plastic casing to eliminate security disputes.

Flying With Lithium Batteries: Getting Familiar With the FAA Carry-On Rules

Lithium batteries carry safety risks because damaged, short-circuited, or overheating cells can experience thermal runaway. Because lithium-battery fires are easier for trained cabin crews to recognize and respond to than fires in checked baggage, aviation regulators tightly control how passengers transport lithium energy storage.

In the United States, commercial flight regulations are established by the Federal Aviation Administration (FAA) PackSafe program and aligned with International Civil Aviation Organization (ICAO) standards. See the FAA Airline Passengers and Batteries guidance and 49 CFR Part 175 for the applicable rules.

These rules generally group ordinary consumer lithium batteries by watt-hour thresholds rather than milliamp-hours:

• Category 1 (Up to 100Wh): Generally permitted for personal use, subject to battery safety requirements, carry-on-only rules for spares and power banks, and airline restrictions (smartphones, laptops, standard power banks).

• Category 2 (101Wh to 160Wh): Maximum of two spare units; strictly requires airline operator pre-approval.

• Category 3 (Over 160Wh): Ordinary consumer lithium batteries and power banks are prohibited in passenger carry-on and checked baggage; specific rules and exceptions apply to qualifying mobility-device batteries.

1. Consumer Electronics and Batteries Up to 100Wh

For lithium-ion batteries up to 100Wh (roughly 27,000mAh at 3.7V), the distinction between installed and spare batteries matters:

• Installed Inside Devices: Laptops, tablets, smartphones, and cameras containing installed batteries under 100Wh can travel in either carry-on bags or checked baggage (though carry-on is strongly encouraged by safety regulators).

• Spare Batteries & Standalone Power Banks: Must travel exclusively in carry-on baggage. Spare lithium packs, uninstalled camera cells, and portable phone chargers are strictly prohibited in checked luggage due to the fire hazard of uncontained cargo hold thermal events.

• Quantity Limits: Travelers are generally permitted a reasonable quantity of under-100Wh spare batteries for personal use.

2. Medium Batteries Between 101Wh and 160Wh

For 101–160Wh batteries used in professional gear, including video production and drones:

• Airline Approval Required: Confirm approval with the operating airline before carrying a battery in this capacity range.

• Strict Quantity Cap: Regulations restrict travelers to a maximum of two spare batteries within this size bracket per passenger.

• Carry-On Only: Like smaller chargers, these spare packs must travel in carry-on baggage with terminals insulated or placed in individual protective sleeves.

3. Batteries Exceeding 160Wh

Ordinary consumer lithium-ion batteries and power banks exceeding 160 watt-hours are prohibited in passenger carry-on and checked baggage. Qualifying mobility-device batteries are subject to separate FAA rules, including specific allowances for certain batteries up to 300Wh. Batteries that cannot travel in passenger baggage must be transported under the applicable hazardous-materials shipping requirements.

Aviation Advisory Note: Individual airlines maintain the legal authority to enforce policies stricter than base FAA standards. Some international carriers restrict total quantities or demand that power banks display factory-printed Wh markings. Always verify your specific airline carrier's hazardous materials guidelines before arriving at the gate.

Why Watt-Hours Matter For Comparing Power Stations

Once energy systems expand beyond pocket accessories into home backup hardware, camper vans, and job sites, rating capacity in milliamp-hours becomes unwieldy and technically misleading.

Consider comparing two larger battery systems using milliamp-hours:

• A heavy mobile battery rated at "50,000mAh"

• A compact home backup module rated at "25,000mAh"

Without knowing their system operating voltages, the first battery appears twice as capable. But if that 50,000mAh unit runs on a 3.7V internal architecture, it stores only 185Wh. If the 25,000mAh system runs on a 51.2V nominal-voltage LiFePO4 battery configuration, it stores 1,280Wh, nearly seven times the nominal energy capacity of the 185Wh battery.

This is why modern portable power stations rate all internal capacity in watt-hours or kilowatt-hours (kWh). Watt-hours allow direct, transparent comparison across disparate DC battery architectures, solar charge controllers, and 120V AC pure sine wave inverters.

To see how watt-hour ratings define real-world use cases, look at modern portable power hardware:

Compact Emergency and Travel Power

Ultra-compact units like the BLUETTI Elite 10 package a 128Wh LiFePO₄ battery with 200W of AC output in a palm-sized portable power station. Its compact design provides a convenient source of backup power for devices such as smartphones, laptops, cameras, and other compatible low-power electronics.

At 128Wh, the Elite 10 has a battery capacity within the 101–160Wh range, for which qualifying lithium batteries and power banks typically require operating-airline approval. Travelers should check with their specific airline before a flight to confirm whether the device is accepted and whether prior approval is required.

On the ground, the 128Wh energy reserve can provide backup power for applications ranging from smartphones and cameras to compatible CPAP equipment and field electronics, with actual runtime depending on the power requirements of the connected devices.

Dedicated Camping and Outdoor Off-Grid Power

Stepping up to systems intended strictly for ground-based vehicle travel, camping, and emergency kits, units like the BLUETTI Elite 30 V2 provide 288Wh of LiFePO4 energy storage paired with a 600W inverter.

At 288Wh, this system sits well beyond airline travel limits, making it a ground-only power hub. Expressed in milliamp-hours, this battery equals 18,000mAh at its native 16V bus, demonstrating why tracking watt-hours is far more practical than comparing raw amp figures when running outdoor coolers or laptops in the field.

High-Capacity Mobile Energy Storage

For severe storm preparedness, RV living, camping, and demanding field applications, power stations can scale well beyond 1,000 watt-hours. The BLUETTI Elite 100 V2 provides 1,024Wh of LiFePO₄ energy storage with a 1,800W continuous AC output.

If this capacity were expressed using the 3.7V convention commonly used for smartphone batteries, the equivalent figure would be approximately 276,750mAh. This is a calculated 3.7V equivalent rather than the power station's actual battery rating, but it demonstrates why watt-hours are more useful than raw milliamp-hours when comparing batteries operating at different voltages. At 1,024Wh, the Elite 100 V2 stores just over 1kWh of energy.

For a hypothetical 100W continuous load, 1,024Wh would provide a theoretical 10.24 hours of operation before conversion losses. In practice, the available runtime would be somewhat lower when powering an AC appliance through the inverter. A refrigerator also does not normally consume its rated wattage continuously because its compressor cycles on and off, so actual runtime depends on the appliance's duty cycle, efficiency, ambient temperature, and startup characteristics.

Matching Numbers to Real Power Needs

Learning how to calculate mAh to Wh cuts through deceptive electronics marketing and gives you an accurate view of your hardware's real capabilities.

Milliamp-hours tell you the amount of electric charge stored in a battery, but watt-hours tell you the actual work that charge can accomplish across your tools, phones, and camping appliances.

Whenever you compare new power gear:

1. Locate the internal nominal voltage printed on the manufacturer's specification plate.
2. Apply the formula: Watt-Hours = (Milliamp-Hours * Nominal Voltage) / 1,000.
3. Check the calculated watt-hour rating against FAA travel limits before packing for a flight.
4. Use watt-hours as your universal measuring stick when shopping for larger home backup and camping setups.

By calculating true watt-hours, you help assess your battery banks against airline capacity limits, match your real runtime demands, and keep your critical gear running wherever you travel.