Use this Wh to mAh Calculator to convert watt-hours into milliamp-hours when you know the battery's voltage. It is useful for power banks, phone batteries, lithium cells, portable electronics, and any comparison where one label gives energy in Wh while another gives charge capacity in mAh.
The conversion is voltage-dependent, so the same watt-hour value can equal very different mAh values at 3.2V, 3.7V, 5V, 12.8V, or another nominal voltage. Enter the voltage that belongs to the rating you are converting, not simply the output voltage you see on a charger or USB port.
Enter watt-hours and the matching battery voltage. The calculator converts energy to amp-hours, then to milliamp-hours, and shows the reverse check so you can verify the result.
The Wh to mAh Calculator uses a direct electrical-unit relationship rather than a battery-performance model. Watt-hours measure energy, while milliamp-hours measure electric charge. Voltage is the bridge between them. Because voltage is part of the equation, there is no single correct way to convert Wh to mAh without knowing the voltage basis of the battery rating.
Formula: mAh = Wh × 1,000 ÷ V
Equivalent charge capacity at the entered voltage:
10 Wh × 1,000 ÷ 3.7 V = 2,702.70 mAh.
Understand what each unit means, why voltage is required, and when the result is useful for comparing batteries and portable power products.
A Wh to mAh conversion starts with the standard relationship between energy, voltage, and charge. One watt-hour equals one watt used for one hour. One amp-hour represents a current of one amp flowing for one hour. Because electrical power equals volts multiplied by amps, battery energy can be written as watt-hours = volts × amp-hours. Rearranging that relationship gives amp-hours = watt-hours ÷ volts. Multiplying amp-hours by 1,000 converts the result to milliamp-hours.
Why does the voltage change the answer so much? A lower-voltage battery needs more amp-hours to contain the same amount of energy, while a higher-voltage battery needs fewer. That is why the Wh to mAh Calculator can return 27,027mAh for 100Wh at 3.7V but only 7,812.5mAh for the same 100Wh at 12.8V. Neither result is “more correct” without context; each describes the same energy at a different voltage. When using the Wh to mAh Calculator for product research, compare the calculated mAh only after confirming that the batteries share the same voltage basis or that converting to mAh serves a specific purpose.
That equation is the core of the Wh to mAh Calculator. It is also the reverse of the relationship used by the site's mAh to Wh calculator. If your source rating is already in milliamp-hours and you want energy instead, the reverse tool is usually clearer because it keeps the direction of the calculation obvious.
Wh tells you how much electrical energy a battery rating represents. It is often a better unit for comparing batteries that operate at different voltages because it already combines voltage and charge capacity into one energy figure.
Explore watt-hour calculationsmAh is one-thousandth of an amp-hour. It is common on phone cells, power banks, small electronics, and replacement batteries, but it does not describe energy by itself unless the associated voltage is also known.
Convert mAh and AhThe same 10Wh equals about 2,703mAh at 3.7V, 2,000mAh at 5V, and only about 781mAh at 12.8V. That difference is not a contradiction; it is exactly why voltage must be part of every Wh-to-mAh conversion.
Check lithium voltage contextA correct calculation needs matching units and a voltage that describes the same battery rating as the watt-hour figure.
Start with the energy rating in watt-hours. Divide by volts to obtain amp-hours, then multiply by 1,000 to convert amp-hours to milliamp-hours. The Wh to mAh Calculator combines those steps into one equation, but keeping the intermediate Ah value visible makes the result easier to audit.
For 37Wh at 3.7V, the calculation is 37 ÷ 3.7 = 10Ah, then 10 × 1,000 = 10,000mAh. Reversing the result gives 10,000mAh ÷ 1,000 × 3.7V = 37Wh.
Use the nominal or rated voltage associated with the Wh value. Do not automatically use a fully charged voltage, a USB output voltage, or a charger setting unless the manufacturer explicitly uses that value for the capacity rating. Power banks are a common source of confusion because internal battery cells may be rated near 3.6V or 3.7V while the output port can supply 5V or higher negotiated voltages.
If the product already lists both Wh and mAh, you can infer the rating basis with V = Wh × 1,000 ÷ mAh. That can help explain why a 20,000mAh power bank may be around 74Wh when the mAh figure is based on approximately 3.7V internal cells rather than 5V USB output.
If two batteries operate at different voltages, Wh is usually the clearer comparison because it represents energy directly. A 10,000mAh pack at 3.7V is 37Wh, while a 10,000mAh pack at 12.8V is 128Wh. The identical mAh labels do not mean the batteries store the same energy.
For system sizing, begin with energy and load requirements rather than trying to maximize mAh. The Lithium Battery Calculator can help connect Ah, Wh, runtime, and daily load sizing for larger battery systems.
This converter performs a mathematical unit conversion. It does not model inverter losses, DC-DC converter efficiency, battery age, temperature, voltage sag, BMS cutoffs, reserve capacity, or the difference between nominal and actually delivered energy. Those factors matter when predicting runtime or usable output.
Use label or datasheet values for rating comparisons, and use measured voltage and energy only when your test method is designed for that purpose. A precise decimal result cannot make an approximate battery label more accurate than the underlying specification.
A Wh to mAh Calculator can make the arithmetic instant, but the usefulness of the answer still depends on the inputs. These checks help you avoid the common situation where the formula is correct but the battery comparison is not.
These checks are especially important for product-label comparisons. The Wh to mAh Calculator tells you what the energy-to-charge relationship would be at the voltage you enter; it does not determine whether that voltage is the correct rating basis. When in doubt, use the manufacturer's datasheet, battery label, or official technical documentation to confirm the nominal pack voltage.
| Energy | Voltage | Equivalent Ah | Equivalent mAh | Typical context |
|---|---|---|---|---|
| 10 Wh | 3.2 V | 3.125 Ah | 3,125 mAh | Single LiFePO4 cell reference |
| 10 Wh | 3.7 V | 2.703 Ah | 2,703 mAh | Common Li-ion label basis |
| 10 Wh | 5 V | 2.000 Ah | 2,000 mAh | 5V energy-equivalent reference |
| 37 Wh | 3.7 V | 10.000 Ah | 10,000 mAh | Portable battery example |
| 74 Wh | 3.7 V | 20.000 Ah | 20,000 mAh | Large power-bank label example |
| 100 Wh | 12.8 V | 7.813 Ah | 7,813 mAh | 12V-class LiFePO4 energy example |
Travel and safety note: airline battery rules are commonly expressed in watt-hours, not mAh. The FAA PackSafe battery guidance explains how Wh is calculated from voltage and Ah, while IATA's battery travel guidance summarizes current passenger restrictions. Rules can vary by airline and jurisdiction, so use the battery's marked Wh rating and check the current carrier requirements before travel.
These examples show how voltage changes the mAh equivalent even when watt-hours stay the same.
Use mAh = 10 × 1,000 ÷ 3.7. The result is approximately 2,702.7mAh. The same energy can also be written as about 2.7027Ah. This is a common type of conversion when comparing a small lithium-ion battery energy label with a capacity label expressed in mAh.
The reverse check is 2,702.7mAh ÷ 1,000 × 3.7V ≈ 10Wh.
Use 74 × 1,000 ÷ 3.7. The result is exactly 20,000mAh. This example is useful for understanding why a power bank advertised as 20,000mAh can also have an energy rating around 74Wh when the mAh figure is based on 3.7V internal cells.
Do not multiply that 20,000mAh rating by 5V unless the manufacturer states that 5V is the basis of the capacity figure.
Use 100 × 1,000 ÷ 12.8. The result is 7,812.5mAh, or 7.8125Ah. The mAh number looks smaller than a 3.7V pack with the same 100Wh because the higher voltage means less amp-hour charge is required to represent the same energy.
For 12V-class battery planning, the 12V Lithium Battery Calculator adds system-level context beyond this unit conversion.
Common questions about watt-hours, milliamp-hours, voltage, power banks, and interpreting a Wh to mAh Calculator result.
Multiply watt-hours by 1,000, then divide by voltage: mAh = Wh × 1,000 ÷ V. For example, 37Wh at 3.7V equals 10,000mAh. Voltage is required because Wh measures energy while mAh measures charge capacity.
No unique mAh value exists without voltage. The same energy corresponds to more mAh at a lower voltage and fewer mAh at a higher voltage. If the voltage is unknown, check the battery label or product datasheet rather than guessing.
Use the voltage that corresponds to the rating you are converting. Many power banks advertise mAh based on internal lithium-ion cell voltage while providing regulated 5V or higher output. Using output voltage with an internal-cell capacity rating mixes two different rating bases and can give a misleading comparison.
10Wh × 1,000 ÷ 3.7V ≈ 2,702.7mAh. At 5V, the same 10Wh would equal 2,000mAh, showing why a Wh-to-mAh answer is always tied to a voltage.
It depends on voltage. At 3.7V, 100Wh is about 27,027mAh. At 5V, it is 20,000mAh. At 12.8V, it is about 7,812.5mAh. Compare the battery's voltage basis before using the number.
No. The basic conversion describes the theoretical relationship between Wh, voltage, Ah, and mAh. Converter losses, inverter efficiency, battery reserve, temperature, aging, and cutoff behavior are separate effects. For runtime, use a dedicated battery runtime calculator with realistic system assumptions.
Not when comparing batteries at different voltages. mAh is convenient when the batteries share a similar voltage, but Wh is generally clearer for energy comparisons because it combines voltage and charge capacity. A larger mAh number does not automatically mean more stored energy.
Not by itself. Runtime also needs the load's power demand and realistic assumptions about usable battery energy and conversion losses. First confirm the battery energy, then use the site's runtime or broader battery capacity calculator for the next planning step.
Use the Wh to mAh Calculator with the voltage printed on the battery or documented by the manufacturer, then compare the result with watt-hours whenever products use different voltages. For the reverse direction, continue with the mAh to Wh tool.
Open mAh to Wh Calculator