# Wh to Ah: how many amp hours?

Converts watt hours to amp hours at a battery’s voltage, Ah = Wh ÷ V, and back, Wh = Ah × V, with mAh and kWh; or finds the voltage from Wh and Ah.

- Page: https://www.acalculator.org/physics/wh-to-ah-calculator
- JSON spec: https://www.acalculator.org/physics/wh-to-ah-calculator.json
- Version: 3a1532d9ba91

## Default answer

Example with the default inputs (Find Amp hours (Ah), Energy (Wh) 100 Wh, Voltage (V) 12 V): 100 Wh at 12 V is 8.33333 Ah (8,333.33 mAh).

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| find | Find | What to work out: amp hours from watt hours, watt hours from amp hours, or the voltage. |
| wh | Energy (Wh) | The battery’s energy in watt hours or kilowatt hours. |
| v | Voltage (V) | The battery’s nominal voltage. |
| q | Charge | The battery’s capacity in amp hours or milliamp hours, in the unit chosen below. |
| qu | Charge unit | Amp hours (Ah) or milliamp hours (mAh): 1 Ah = 1,000 mAh. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| result | Answer | The value found, to 6 significant figures, with a second unit for amp hours and watt hours. |
| ah | Charge, Ah | The capacity in amp hours: Wh ÷ V. |
| mah | Charge, mAh | The capacity in milliamp hours: Ah × 1,000. |
| wh | Energy, Wh | The energy in watt hours: Ah × V. |
| kwh | Energy, kWh | The energy in kilowatt hours: Wh ÷ 1,000. |
| volts | Voltage, V | The voltage: Wh ÷ Ah. |

## Method

Ah = Wh ÷ V; Wh = Ah × V; V = Wh ÷ Ah. 1 Ah = 1,000 mAh; 1 kWh = 1,000 Wh.

## Assumptions

- The voltage is the battery’s nominal (average) voltage; the real voltage falls as a battery drains.
- Typed values are read as the exact decimals you typed; each result is rounded once to show.

## Worked examples

1. find = ah, wh = 360,000, v = 12 gives ah = 8.33333, mah = 8,333.33, result = 8.33333 Ah (8,333.33 mAh). Source: NIST Special Publication 811 (2008), Chapter 4, Table 3: the volt is W/A, the coulomb s·A, the watt J/s, https://www.nist.gov/pml/special-publication-811/nist-guide-si-chapter-4-two-classes-si-units-and-si-prefixes (retrieved 2026-10-19); NIST Special Publication 811, Appendix B.8: ampere hour = 3.6 × 10³ C and watt hour = 3.6 × 10³ J, exact, https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b8 (retrieved 2026-10-19).
2. find = wh, q = 5,000, qu = mAh, v = 3.7 gives wh = 18.5, kwh = 0.0185, ah = 5, result = 18.5 Wh (0.0185 kWh). Source: NIST Special Publication 811 (2008), Chapter 4, Table 3: the volt is W/A, the coulomb s·A, the watt J/s, https://www.nist.gov/pml/special-publication-811/nist-guide-si-chapter-4-two-classes-si-units-and-si-prefixes (retrieved 2026-10-19).
3. find = volts, wh = 180,000, q = 4,000, qu = mAh gives volts = 12.5, result = 12.5 V. Source: NIST Special Publication 811 (2008), Chapter 4, Table 3: the volt is W/A, the coulomb s·A, the watt J/s, https://www.nist.gov/pml/special-publication-811/nist-guide-si-chapter-4-two-classes-si-units-and-si-prefixes (retrieved 2026-10-19).
4. find = ah, wh = 48,600,000, v = 48 gives ah = 281.25, wh = 13,500, result = 281.25 Ah (281,250 mAh). Source: NIST Special Publication 811 (2008), Chapter 4, Table 3: the volt is W/A, the coulomb s·A, the watt J/s, https://www.nist.gov/pml/special-publication-811/nist-guide-si-chapter-4-two-classes-si-units-and-si-prefixes (retrieved 2026-10-19); NIST Special Publication 811, Appendix B.8: ampere hour = 3.6 × 10³ C and watt hour = 3.6 × 10³ J, exact, https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b8 (retrieved 2026-10-19).

## FAQ

### How do you convert Wh to Ah?

Divide the watt hours by the voltage: Ah = Wh ÷ V. A 100 Wh battery at 12 V holds 100 ÷ 12 = 8.33 Ah.

### How do you convert Ah to Wh?

Multiply the amp hours by the voltage: Wh = Ah × V. A 5,000 mAh phone battery (5 Ah) at 3.7 V stores 5 × 3.7 = 18.5 Wh.

### Why do I need the voltage to convert Wh to Ah?

Watt hours measure energy and amp hours measure charge. A volt is a watt per amp (NIST SP 811), so energy = charge × voltage: the same 8.33 Ah holds 100 Wh at 12 V but 200 Wh at 24 V.

### How many mAh is 1 Wh?

It depends on the voltage: 1 Wh ÷ 3.7 V = 0.27027 Ah = 270.27 mAh for a lithium-ion cell, and 1 Wh ÷ 12 V = 83.33 mAh for a 12 V battery.

### How many amp hours is a 13.5 kWh battery?

At 48 V, 13,500 Wh ÷ 48 V = 281.25 Ah. Give the battery’s own nominal voltage, since the answer depends on it.

### What voltage should I use?

The battery’s nominal voltage from its label: 3.6 or 3.7 V for one lithium-ion cell, 12 V for a lead-acid car battery. The real voltage falls as the battery drains, so the result is the rated capacity.

## Sources

- NIST Special Publication 811 (2008), Chapter 4, Table 3 (the 22 SI coherent derived units with special names): the volt is W/A, the coulomb s·A, the watt J/s, retrieved 2026-10-19. https://www.nist.gov/pml/special-publication-811/nist-guide-si-chapter-4-two-classes-si-units-and-si-prefixes
- NIST Special Publication 811, Appendix B.8: ampere hour (A·h) = 3.6 × 10³ C, watt hour (W·h) = 3.6 × 10³ J and kilowatt hour = 3.6 × 10⁶ J, all exact, retrieved 2026-10-19. https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b8