Convert mAh to Wh

The mAh to Wh Calculator converts battery capacity from milliamp-hours into watt-hours using the battery voltage. This is one of the most useful conversions for comparing lithium batteries because mAh only tells you how much charge the battery can store, while Wh tells you how much usable energy is available. A 3000mAh battery at 3.7V is not the same energy as a 3000mAh battery at 12V, so voltage must always be included when comparing real battery capacity.

Use this calculator for power banks, 18650 cells, 21700 cells, Li-ion packs, LiPo batteries, LiFePO4 batteries, USB battery packs, RC batteries, solar storage, portable electronics, and backup power planning. Enter the battery capacity in mAh and the nominal voltage, then the calculator will show the equivalent energy in watt-hours. The standard formula is simple: Wh = (mAh × Voltage) ÷ 1000.

mAh to Wh Calculator

mAh to Wh Conversion Formula

The formula for converting milliamp-hours to watt-hours is:

Wh = (mAh × Voltage) ÷ 1000

The division by 1000 is used because mAh means milliamp-hours, and 1000 milliamps equals 1 amp. When capacity is written as 3000mAh, it is the same as 3Ah. Watt-hours are then found by multiplying amp-hours by voltage. For example, 3000mAh × 3.7V ÷ 1000 = 11.1Wh. This tells you that a typical 3000mAh lithium-ion cell stores about 11.1 watt-hours of energy at its nominal voltage.

This conversion is especially important because mAh can be misleading when voltage is different. A 10000mAh power bank is usually rated at the internal lithium cell voltage of 3.7V, not the 5V USB output. That means 10000mAh × 3.7V ÷ 1000 = 37Wh before conversion losses. A 10000mAh battery pack at 12V, however, would be 120Wh. Both have the same mAh number, but the 12V pack stores more than three times the energy.

For quick manual calculations, first convert mAh to Ah by dividing by 1000. Then multiply Ah by voltage. A 20000mAh battery is 20Ah. At 3.7V, 20Ah × 3.7V = 74Wh. At 3.2V, 20Ah × 3.2V = 64Wh. At 12V, 20Ah × 12V = 240Wh. This is why every meaningful mAh-to-Wh calculation must include voltage.

How to Use This mAh to Wh Calculator

Start by entering the battery capacity in mAh. This number is usually printed on the battery label, power bank case, cell datasheet, or product specification page. Common values include 2000mAh, 3000mAh, 5000mAh, 10000mAh, 20000mAh, and 50000mAh. For battery packs, the displayed capacity may refer to the cell group capacity, the pack capacity, or the output capacity, so it is best to check the manufacturer wording before making a final decision.

Next, enter the nominal voltage. Nominal voltage is the average voltage used for energy calculations, not the fully charged voltage and not the empty voltage. Most Li-ion and LiPo cells use a nominal voltage of 3.7V. Many LiFePO4 cells use a nominal voltage of 3.2V. A 12V lithium pack is often around 12.8V nominal if it is LiFePO4, while a 24V system may be around 25.6V and a 48V system may be around 51.2V. You can enter the exact nominal voltage from the datasheet for the most accurate result.

The calculator will show three useful outputs: watt-hours, amp-hours, and the formula used. Watt-hours are best for comparing energy. Amp-hours are useful for matching charger and BMS specifications. The formula line helps you verify that the result follows the standard conversion. For example, entering 3000mAh and 3.7V gives 11.1Wh because 3000 × 3.7 ÷ 1000 = 11.1.

Why Use Our mAh to Wh Calculator

Power Bank Energy

Convert power bank capacity from mAh to Wh so you can understand the real energy stored inside the cells. This is more useful than mAh alone when comparing different USB battery packs.

Lithium Battery Comparison

Compare Li-ion, LiPo, and LiFePO4 batteries using watt-hours instead of capacity alone. Wh makes comparisons fair because it includes both capacity and voltage.

Airline Travel Planning

Many travel rules describe battery limits in Wh, while power banks are often sold in mAh. Converting mAh to Wh helps you check the size category of a portable battery.

Runtime Estimates

Battery runtime is usually calculated from watt-hours divided by load watts. Converting mAh to Wh gives you the energy number needed for runtime planning.

Pack Design

When building series and parallel battery packs, Wh helps you calculate total stored energy. This is useful for e-bikes, RC packs, solar storage, and portable power projects.

Specification Checking

Use the calculator to verify product claims. If a battery lists mAh and voltage, you can quickly check whether the advertised Wh rating is reasonable.

Common mAh to Wh Conversions

Here are common lithium battery conversions using the standard Li-ion nominal voltage of 3.7V. These values are often seen in smartphones, tablets, USB power banks, flashlights, small electronics, and portable battery packs.

  • 2000mAh at 3.7V = 7.4Wh. This is a small single-cell battery size often used in compact electronics.
  • 3000mAh at 3.7V = 11.1Wh. This is a common capacity for modern cylindrical lithium-ion cells and many smartphone-class batteries.
  • 5000mAh at 3.7V = 18.5Wh. This is common for high-capacity phone batteries, small power banks, and portable devices.
  • 10000mAh at 3.7V = 37Wh. This is a standard power bank size and a useful reference point for portable charging.
  • 20000mAh at 3.7V = 74Wh. This is a larger power bank size often used for phones, tablets, cameras, and travel charging.
  • 30000mAh at 3.7V = 111Wh. This is a high-capacity portable battery size where travel, shipping, and device compatibility checks become more important.
  • 50000mAh at 3.7V = 185Wh. This is closer to a compact portable power station than a normal pocket power bank.

For LiFePO4 cells, the voltage is usually 3.2V, so the Wh value is lower for the same mAh rating. A 10000mAh LiFePO4 cell group at 3.2V equals 32Wh. A 20000mAh LiFePO4 battery at 3.2V equals 64Wh. This does not mean LiFePO4 is worse; it simply uses a different chemistry with a different nominal voltage. LiFePO4 is often chosen for long cycle life, thermal stability, and safety-focused battery systems.

Understanding mAh, Ah, Wh, and Voltage

mAh stands for milliamp-hours. It measures electric charge capacity, not energy by itself. A battery with a 3000mAh rating can theoretically deliver 3000 milliamps for one hour, 1500 milliamps for two hours, or 300 milliamps for ten hours under ideal conditions. In practice, actual results depend on load current, temperature, age, discharge cutoff, conversion losses, and the battery management system.

Ah stands for amp-hours. It is the same type of capacity measurement as mAh, but expressed in larger units. To convert mAh to Ah, divide by 1000. For example, 3000mAh is 3Ah, 10000mAh is 10Ah, and 20000mAh is 20Ah. Battery systems used in RVs, boats, solar storage, and backup power are commonly rated in Ah because their capacity is much larger than small phone or power bank batteries.

Wh stands for watt-hours. This is a measurement of energy. It combines capacity with voltage, so it is much better for comparing different battery types and voltages. A 12V 10Ah battery has 120Wh, while a 3.7V 10Ah battery has 37Wh. Both are 10000mAh, but the 12V battery stores much more energy because it operates at a higher voltage.

Voltage is the electrical pressure of the battery system. Lithium batteries do not stay at one exact voltage during use, so calculations usually use nominal voltage. A single Li-ion cell may be 4.2V when full, around 3.7V nominal, and about 3.0V near empty depending on the cutoff. A LiFePO4 cell may be around 3.65V full, 3.2V nominal, and lower near discharge cutoff. Nominal voltage gives a practical average value for estimating energy.

Li-ion, LiPo, and LiFePO4 Nominal Voltage

Most consumer lithium-ion batteries use 3.6V or 3.7V nominal voltage. The difference between 3.6V and 3.7V is usually small for rough estimates, but datasheet values should be used for formal calculations. If a 3000mAh cell is rated at 3.6V, the energy is 10.8Wh. If the same capacity is rated at 3.7V, the energy is 11.1Wh. The formula is the same; only the voltage value changes.

LiPo batteries used in drones, RC vehicles, hobby packs, and compact electronics are commonly calculated at 3.7V per cell. A 2S LiPo pack has two cells in series and is about 7.4V nominal. A 3S LiPo pack is about 11.1V nominal. A 4S pack is about 14.8V nominal. To convert pack capacity to Wh, multiply the pack mAh by the pack voltage, not just the voltage of one cell. For example, a 5000mAh 3S LiPo pack is 5000 × 11.1 ÷ 1000 = 55.5Wh.

LiFePO4 batteries use about 3.2V nominal per cell. A 4S LiFePO4 pack is often described as a 12V lithium battery and is about 12.8V nominal. An 8S pack is about 25.6V nominal, and a 16S pack is about 51.2V nominal. If you are converting mAh to Wh for a full LiFePO4 battery pack, use the pack nominal voltage, not the single-cell voltage, unless the capacity rating is specifically for one cell only.

Power Bank mAh vs Real Output Energy

Power banks can be confusing because their printed mAh rating is usually based on the internal lithium cell voltage, often 3.7V. The USB output may be 5V, 9V, 12V, or 20V depending on the charging protocol. A 10000mAh power bank is usually about 37Wh internally, not 50Wh at 5V. After conversion losses, the usable output energy is lower than the internal cell energy.

For example, a 10000mAh power bank at 3.7V stores about 37Wh. If the boost converter is 85% efficient, usable output energy might be around 31.45Wh. At 5V output, that equals about 6.29Ah or 6290mAh delivered at 5V. This is why a phone may not receive the full printed mAh rating from a power bank. The number on the case refers to the cell capacity, while the device receives energy after voltage conversion.

When comparing power banks, watt-hours are more transparent than mAh because Wh expresses actual stored energy. A power bank advertised as 20000mAh at 3.7V is about 74Wh. If another pack is advertised as 20000mAh at 5V output capacity, that would be 100Wh. These are not identical claims. Always check whether the specification is cell capacity, rated output capacity, or tested usable output capacity.

Battery Pack Examples

Example 1: 3000mAh Li-ion cell. A 3000mAh lithium-ion cell at 3.7V equals 11.1Wh. This is calculated as 3000 × 3.7 ÷ 1000 = 11.1Wh. If four of these cells are connected in parallel, the pack becomes 12000mAh at 3.7V, or 44.4Wh. If the same four cells are connected in series, the pack becomes 3000mAh at 14.8V, also 44.4Wh. Series increases voltage; parallel increases Ah; total energy depends on the total number of cells.

Example 2: 5000mAh 3S LiPo pack. A 3S LiPo pack has a nominal voltage of 11.1V. The energy is 5000 × 11.1 ÷ 1000 = 55.5Wh. This is a common calculation for drones, RC cars, portable electronics, and hobby battery packs. For runtime estimates, divide 55.5Wh by the load watts, then adjust for efficiency and safe discharge limits.

Example 3: 100Ah LiFePO4 battery. Large lithium batteries are usually written in Ah instead of mAh. A 100Ah battery is 100000mAh. If the pack is 12.8V nominal, the energy is 100000 × 12.8 ÷ 1000 = 1280Wh. This is the same as 1.28kWh. A battery like this is used for RVs, solar systems, trolling motors, portable power stations, and backup power.

Common Mistakes to Avoid

The most common mistake is comparing mAh values without voltage. A 20000mAh 3.7V power bank and a 20000mAh 12V battery are not equal in energy. The first is about 74Wh, while the second is about 240Wh. Whenever voltage changes, mAh alone cannot describe the battery stored energy.

Another mistake is using full-charge voltage instead of nominal voltage for energy estimates. A single Li-ion cell may charge to 4.2V, but its nominal voltage is usually around 3.7V. Using 4.2V will overstate the typical energy. Datasheets list nominal voltage for a reason: it provides a more realistic average for capacity and energy calculations.

A third mistake is forgetting efficiency losses. The mAh to Wh formula calculates stored battery energy from nominal capacity and voltage. It does not automatically subtract losses from DC-DC converters, inverters, wiring, heat, high current draw, or battery age. For real runtime, convert mAh to Wh first, then multiply by expected efficiency and divide by the load power.

Finally, be careful with battery packs that list both cell capacity and output capacity. A product may advertise 50000mAh, but that may refer to internal cells at 3.7V. The usable output at 5V or 20V will be different after conversion. If the manufacturer provides a Wh rating, that is usually the better number for comparison.

mAh to Wh Design Checklist

  • Find the capacity rating in mAh from the battery label, datasheet, or product specification.
  • Identify the correct nominal voltage for the cell or battery pack.
  • Use the formula Wh = (mAh × Voltage) ÷ 1000.
  • For multi-cell packs, use the total pack voltage when the mAh rating applies to the full pack.
  • For power banks, remember that printed mAh is often based on internal cell voltage, not USB output voltage.
  • For runtime planning, use Wh rather than mAh because loads are usually rated in watts.
  • Apply efficiency losses for DC converters, inverters, wiring, and real-world use.
  • Check manufacturer specifications for exact nominal voltage, minimum voltage, maximum voltage, and usable capacity.
  • Use Wh or kWh when comparing batteries across different voltages and chemistries.
  • Verify critical travel, shipping, safety, and design decisions with official product documents.

Related Tools

After converting mAh to Wh, you may also need to convert Wh back to mAh, convert mAh to Ah, calculate battery runtime, or estimate battery charging time. The most common next step is runtime planning: once you know the watt-hours, divide Wh by the load in watts to estimate operating time. For example, a 74Wh power bank powering a 10W device may run for about 7.4 hours before efficiency losses. If the converter is 85% efficient, usable runtime may be closer to 6.3 hours.

Frequently Asked Questions

How do you convert mAh to Wh?
Use the formula Wh = (mAh × V) ÷ 1000. For example, a 3000mAh battery at 3.7V is 3000 × 3.7 ÷ 1000 = 11.1Wh. The voltage must be included because mAh alone does not describe total stored energy.
What is 10000mAh in Wh?
At the standard Li-ion nominal voltage of 3.7V, 10000mAh equals 37Wh. The calculation is 10000 × 3.7 ÷ 1000 = 37Wh. If the battery voltage is different, the Wh result will also be different.
What is 20000mAh in Wh?
At 3.7V, 20000mAh equals 74Wh. The calculation is 20000 × 3.7 ÷ 1000 = 74Wh. At 3.2V, the same 20000mAh equals 64Wh. At 12V, it equals 240Wh.
Why do I need voltage to convert mAh to Wh?
mAh measures charge capacity, while Wh measures energy. Energy depends on both capacity and voltage. Without voltage, a mAh number cannot tell you how much work the battery can actually do or how long it can power a device.
Is 10000mAh always 37Wh?
No. 10000mAh is 37Wh only when the nominal voltage is 3.7V. At 3.2V, it is 32Wh. At 5V, it is 50Wh. At 12V, it is 120Wh. Always use the correct nominal voltage for the battery or output rating being converted.
What voltage should I use for a power bank?
Most power banks advertise mAh based on internal Li-ion cells, usually 3.7V nominal. If the manufacturer lists a different nominal voltage or provides a Wh rating, use the manufacturer value. USB output voltage should only be used if the capacity rating specifically refers to output capacity.
How many Wh is a 5000mAh battery?
At 3.7V, a 5000mAh battery is 18.5Wh. The formula is 5000 × 3.7 ÷ 1000 = 18.5Wh. At 3.2V, it would be 16Wh. At 7.4V, it would be 37Wh.
Can I use Wh to estimate battery runtime?
Yes. After converting mAh to Wh, divide the watt-hours by the load in watts. For example, a 37Wh battery powering a 10W device has an ideal runtime of 3.7 hours. Real runtime will be lower after efficiency losses, cutoff limits, temperature effects, and battery aging.