acalculator

Wh to Ah: how many amp hours?

Wh to Ah: type a battery’s energy in watt hours and its voltage to get its capacity in amp hours and mAh. The Wh to Ah calculator also turns Ah or mAh back into Wh, or finds the voltage.

Your numbers

Units
Find
Answer
8.33333 Ah (8,333.33 mAh)

100 Wh at 12 V is 8.33333 Ah (8,333.33 mAh).

Charge, Ah
8.33333
Charge, mAh
8,333.33
Energy, Wh
100
Energy, kWh
0.1
Voltage, V
12

Answer: 8.33333 Ah (8,333.33 mAh). 100 Wh at 12 V is 8.33333 Ah (8,333.33 mAh).

How to calculate

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.

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).

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

  • 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.

Machine-readable copies: Markdown, JSON.

Worked examples

Each example is checked against the calculator on every build.

  1. Find Amp hours (Ah), Energy (Wh) 100 Wh, Voltage (V) 12 V gives Charge, Ah 8.33333, Charge, mAh 8,333.33, Answer 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 Watt hours (Wh), Charge 5,000, Charge unit mAh, Voltage (V) 3.7 V gives Energy, Wh 18.5, Energy, kWh 0.0185, Charge, Ah 5, Answer 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 (V), Energy (Wh) 50 Wh, Charge 4,000, Charge unit mAh gives Voltage, V 12.5, Answer 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 Amp hours (Ah), Energy (Wh) 13,500 Wh, Voltage (V) 48 V gives Charge, Ah 281.25, Energy, Wh 13,500, Answer 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)

How it works

A volt is a watt per ampere (1 V = 1 W/A), so a watt hour is a volt times an amp hour: Wh = V × Ah. Choose what to find:

  • Amp hours: Ah = Wh ÷ V.
  • Watt hours: Wh = Ah × V.
  • Volts: V = Wh ÷ Ah.

The page shows the capacity in Ah and mAh (Ah × 1,000), the energy in Wh and kWh (Wh ÷ 1,000), and the voltage. The answer line reads a Ah (b mAh) for amp hours, a Wh (b kWh) for watt hours, and a V for volts.

Units (exact): 1 kWh = 1,000 Wh; 1 Ah = 1,000 mAh; 1 mV = 0.001 V; 1 kV = 1,000 V. In SI, 1 Wh = 3,600 J and 1 Ah = 3,600 C, so the 3,600 cancels in Wh ÷ Ah.

Rules

  • Energy from 10⁻¹² Wh to 10¹² Wh; voltage from 10⁻⁹ V to 10⁹ V; charge from 10⁻¹² to 10¹² in the unit chosen beside it (Ah or mAh). Limits include their ends; a value typed in another unit is converted first.
  • The voltage is the battery's nominal voltage. Every value is positive.

Output format

The answer line and every number show to 6 significant figures, rounded half up, with trailing zeros dropped, thousands commas, and from 10¹⁵ up or below 10⁻⁶ as a × 10ⁿ. Typed values are read back as the exact decimals you typed, so each result is an exact fraction rounded once.

The answer sentence reads W Wh at V V is A Ah (M mAh)., with each number written as its output is.

Worked examples by hand

100 Wh at 12 V. Ah = 100 ÷ 12 = 8.33333 Ah (8,333.33 mAh).

A phone battery. 5,000 mAh = 5 Ah at 3.7 V: Wh = 5 × 3.7 = 18.5 Wh (0.0185 kWh).

The voltage. 50 Wh and 4,000 mAh = 4 Ah: V = 50 ÷ 4 = 12.5 V.

A home battery. 13.5 kWh = 13,500 Wh at 48 V: Ah = 13,500 ÷ 48 = 281.25 Ah (281,250 mAh).

Other questions people ask

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.