Quick answer
Energy in watt-hours = amp-hours × volts. A 100 Ah battery at 12 V stores 1,200 Wh (1.2 kWh). The converter also works in reverse: Ah = Wh ÷ V.
Choose the direction, enter the value and the voltage. The calculator returns the converted figure.
Related tools: kW to VA Converter: Apparent power in VA from real power and power factor.
How to use the Ah ⇄ Wh Converter
- Choose convert: Ah → Wh, Wh → Ah, mAh → Wh and Wh → mAh.
- Enter value (above 0).
- Enter voltage (V) (above 0).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Convert | Choose one: Ah → Wh; Wh → Ah; mAh → Wh; Wh → mAh | Starts at Ah → Wh |
| Value | A number | > 0 |
| Voltage | A number, in V | > 0 |
Formula and method
Formula
Wh = Ah × V
IEEE-754 double precision; shown to the decimals indicated.
Energy equals charge times voltage; use the battery's nominal voltage.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Convert = Ah → Wh; Value = 100; Voltage = 12.
| Result | Value |
|---|---|
| Energy | 1,200 Wh |
Example 2
Inputs: Convert = Wh → Ah; Value = 1200; Voltage = 12.
| Result | Value |
|---|---|
| Capacity | 100 Ah |
Example 3
Inputs: Convert = mAh → Wh; Value = 5000; Voltage = 3.7.
| Result | Value |
|---|---|
| Energy | 18.5 Wh |
The first line is the headline result (energy). IEEE-754 double precision; shown to the decimals indicated.
Why voltage is needed
Amp-hours measure charge, not energy. The same 100 Ah stores 1,200 Wh at 12 V but 4,800 Wh at 48 V. Always use the battery's nominal voltage, for example 3.7 V for a lithium cell or 12.8 V for LiFePO4.
Nominal voltage
Voltage falls as a battery discharges, so the figure is a nominal energy. Usable energy is also lower than rated, especially for lead-acid batteries that should not be fully discharged. Airlines limit spare lithium batteries by Wh, commonly to 100 Wh without approval.
How the result changes with value
Holding every other input at the first worked example, this table changes only value. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Value | Energy |
|---|---|
| 50 | 600 Wh |
| 100 | 1,200 Wh |
| 200 | 2,400 Wh |
| 400 | 4,800 Wh |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Value: entering "0" shows "Value must be greater than 0." beside that field and no result.
- Voltage: entering "0" shows "Voltage must be greater than 0." beside that field and no result.
Choosing between the Ah ⇄ Wh Converter and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [kW to VA Converter](/converters/kw-to-va-calculator/) | real power and power factor | Apparent power |
| [Ohm's Law Calculator](/engineering/ohm-s-law-calculator/) | Current | |
| [Parallel Resistor Calculator](/engineering/parallel-resistor-calculator/) | resistances | Parallel resistance |
| [Watt-Hours Calculator](/engineering/watt-hours/) | use | Energy |
| [LC Resonant Frequency Calculator](/engineering/resonant-frequency-lc/) | inductance and capacitance | Resonant frequency |
Background: unit conversion
Many customary units are defined exactly in terms of metric ones: since the 1959 International Yard and Pound Agreement an inch is exactly 2.54 cm and a pound is exactly 0.45359237 kg (NIST SP 811 lists these). So most length and mass conversions are exact apart from the rounding of the displayed result.
To convert, multiply the value by the source unit's factor to reach the base unit, then divide by the target unit's factor; the unit table on this page lists every factor used. Temperature and fuel economy are the exceptions, because they are not simple multiples.
Assumptions and limitations
- Nominal voltage varies with state of charge
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for value and voltage to confirm this.
Frequently asked questions
How many Wh is a 10,000 mAh power bank?
At 3.7 V it is about 37 Wh.
Is Wh the same as kWh?
A kilowatt-hour is 1,000 watt-hours.
How long does the battery last?
Divide the Wh by the load in watts.
What does the Ah ⇄ Wh Converter calculate?
Convert between amp-hours, milliamp-hours and watt-hours. It returns Energy.
What formula does the Ah ⇄ Wh Converter use?
Wh = Ah × V. Energy equals charge times voltage; use the battery's nominal voltage.
What do I need to enter in the ah ⇄ Wh Converter?
You enter Convert, Value and Voltage (V).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Nominal voltage varies with state of charge.
What does the “Convert” option change?
It sets how the ah ⇄ Wh is worked out. The choices are Ah → Wh, Wh → Ah, mAh → Wh and Wh → mAh.
What is an example of a ah ⇄ Wh result?
With convert Ah → Wh, value 100 and voltage 12, the energy is 1,200 Wh.
Where does the method come from?
The method follows: Definition of watt-hour and ampere-hour.
Related calculators
- kW to VA Converter — Apparent power in VA from real power and power factor.
- Power Factor Calculator — Power factor, phase angle and reactive power from real and apparent power.
- Digital Storage Converter — Convert bits, bytes and decimal or binary multiples.
- Angle Converter — Convert degrees, radians, gradians, arcminutes and turns.
- Illuminance Converter — Convert lux, foot-candles and phot.
Sources
- Definition of watt-hour and ampere-hour
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.