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Amp-Hours to Watt-Hours Calculator

Convert battery capacity from amp-hours (Ah) to watt-hours (Wh). Useful for comparing power banks, laptop batteries, and calculating device runtime.

Calculate Wh from Amp-Hours

Battery Capacity (Ah)

Battery Voltage (V)

Common: 3.7V (single Li-ion), 7.4V (2-cell), 11.1V (3-cell), 12V (lead-acid)

Ah to Wh Formula

Wh = Ah × V

Where Wh is energy in watt-hours, Ah is capacity in amp-hours, and V is voltage in volts.

Example

A 20,000 mAh (20 Ah) power bank at 3.7V:
Wh = 20 × 3.7 = 74 Wh

What Is Ah to Wh Conversion?

Ampere-hours (Ah) to watt-hours (Wh) conversion is a fundamental calculation in electrical engineering and battery technology. While Ah measures the charge a battery can deliver, Wh measures the actual energy stored by incorporating voltage: Wh = Ah × V. This conversion is critical for comparing batteries, sizing power systems, and calculating device runtime. Consumer electronics typically use Wh or mAh ratings, while industrial batteries use Ah. Understanding this relationship is essential for anyone working with portable electronics, renewable energy systems, or electric vehicles.

How to Calculate Ah to Wh Conversion

1
Find the Ah Rating
Locate the ampere-hour capacity on your battery. Smartphone batteries are typically 3-5Ah (3000-5000mAh), laptop batteries 50-100Wh, and car batteries 45-80Ah.
2
Determine the Voltage
Find the nominal voltage. Lithium-ion cells are 3.7V nominal, lead-acid cells are 2V (12V for 6-cell), and NiMH cells are 1.2V.
3
Calculate Watt-Hours
Multiply Ah × V to get Wh. A 5Ah battery at 3.7V = 18.5Wh. This represents the total energy the battery can theoretically deliver.
4
Apply to Runtime Calculations
Divide Wh by your device power consumption in watts to estimate runtime in hours. An 18.5Wh battery powering a 5W device lasts approximately 3.7 hours.

Why Ah to Wh Conversion Matters

Airline Battery Regulations

FAA and IATA limit lithium batteries to 100Wh for carry-on luggage without approval, and 160Wh with airline approval. Converting Ah to Wh determines if your battery is flight-compliant.

Device Runtime Estimation

Knowing battery energy in Wh allows you to calculate how long devices will operate. This is critical for field equipment, medical devices, and emergency backup systems.

Battery Replacement Compatibility

When replacing batteries, matching Wh ensures equivalent energy capacity. A replacement battery with the same Ah but different voltage will provide different energy and may not be compatible.

Energy Cost Calculations

Electricity is billed in kWh. Converting battery Wh to kWh (divide by 1000) helps calculate the cost to charge batteries and compare operating costs of battery-powered vs grid-powered equipment.

Electrical Safety Tips & Best Practices

mAh to Wh Conversion

For milliamp-hour ratings common on smartphone batteries, divide mAh by 1000 first to get Ah, then multiply by voltage. A 5000mAh 3.7V battery = 18.5Wh.

Check Battery Chemistry

Different chemistries have different nominal voltages per cell: Li-ion 3.7V, LiFePO4 3.2V, NiMH 1.2V, Lead-acid 2.0V. Using the wrong voltage gives incorrect Wh values.

Real-World Capacity Loss

Actual usable Wh is typically 80-95% of rated capacity due to internal resistance, voltage sag under load, and cut-off voltage limitations of the device.

Temperature Compensation

Battery capacity drops in extreme temperatures. Subtract 10-20% from calculated Wh for cold weather operation (below 0°C/32°F) when planning critical applications.

Ah to Wh Conversion Chart

Ah	3.7V	5V	7.4V	11.1V	12V
1 Ah	3.7 Wh	5 Wh	7.4 Wh	11.1 Wh	12 Wh
2 Ah	7.4 Wh	10 Wh	14.8 Wh	22.2 Wh	24 Wh
5 Ah	18.5 Wh	25 Wh	37 Wh	55.5 Wh	60 Wh
10 Ah	37 Wh	50 Wh	74 Wh	111 Wh	120 Wh
20 Ah	74 Wh	100 Wh	148 Wh	222 Wh	240 Wh
50 Ah	185 Wh	250 Wh	370 Wh	555 Wh	600 Wh
100 Ah	370 Wh	500 Wh	740 Wh	1110 Wh	1200 Wh
200 Ah	740 Wh	1000 Wh	1480 Wh	2220 Wh	2400 Wh

Common Device Battery Capacities

Device	Capacity	Voltage	Energy
Power Bank (Small)	5 Ah	3.7V	18.5 Wh
Power Bank (Large)	20 Ah	3.7V	74 Wh
Smartphone Battery	3-5 Ah	3.7V	11-18.5 Wh
Laptop Battery (2-cell)	4-5 Ah	7.4V	30-37 Wh
Laptop Battery (6-cell)	5-6 Ah	11.1V	55-67 Wh
Drone Battery	3-5 Ah	11.1-14.8V	33-74 Wh
E-Bike Battery	10-20 Ah	36-48V	360-960 Wh
12V Car Battery	50-80 Ah	12V	600-960 Wh

Frequently Asked Questions

How many Wh is a 10,000 mAh power bank?

At the internal 3.7V: 10 Ah × 3.7V = 37 Wh. This is the actual energy stored.

Why is Wh a better comparison than mAh?

Wh accounts for voltage differences. A 5,000 mAh phone battery at 3.7V has the same energy as a 1,850 mAh battery at 10V. Wh makes these comparable.

What's the airline limit for batteries?

Most airlines allow batteries under 100 Wh in carry-on. From 100-160 Wh requires airline approval. Over 160 Wh is prohibited. A 20,000 mAh power bank at 3.7V is 74 Wh, which is within the limit.

How many phone charges from a power bank?

Divide power bank Wh by phone battery Wh, then multiply by ~0.8 for losses. Example: 74 Wh power bank ÷ 14 Wh phone battery × 0.8 = about 4 full charges.

How many Wh is a 5000mAh battery?

A 5000mAh (5Ah) battery at the typical smartphone voltage of 3.7V equals 18.5Wh (5 × 3.7 = 18.5). At 3.85V (common for newer lithium-polymer cells), it equals 19.25Wh. The exact Wh depends on the cell nominal voltage.

Can I bring a 100Wh battery on a plane?

Yes, lithium batteries up to 100Wh are allowed in carry-on luggage by FAA regulations without special approval. Batteries between 100-160Wh require airline approval. Batteries over 160Wh are prohibited on passenger aircraft. Always carry spare batteries in carry-on, never checked luggage.

What is the difference between Ah and Wh?

Ah measures electrical charge (how many amps for how many hours), while Wh measures energy (charge × voltage). A 10Ah 12V battery has 120Wh, but a 10Ah 24V battery has 240Wh — same charge capacity but double the energy because voltage is doubled.

How do I calculate battery runtime from Wh?

Divide the battery Wh by the device power consumption in watts. For example, a 50Wh laptop battery powering a laptop consuming 10W will last approximately 5 hours (50 ÷ 10 = 5). Account for 85-90% efficiency in practice.

Why do laptop batteries show Wh but phone batteries show mAh?

Laptop batteries contain multiple cells at varying voltages (10.8V, 11.1V, 14.8V), making Wh a clearer energy comparison. Phone batteries are single cells at a standard 3.7-3.85V, so mAh works well since voltage is consistent across manufacturers.

References & Industry Standards

IEC 62133 - Safety Requirements for Portable Sealed Secondary Cells
FAA Advisory - Safe Travel with Batteries and Devices
UN Manual of Tests and Criteria Section 38.3 - Lithium Battery Transport
IEEE 1725 - Rechargeable Batteries for Cellular Telephones

Last updated: 2026-02-01 | Reviewed by UnitTables Engineering Team

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What Is Ah to Wh Conversion?

How to Calculate Ah to Wh Conversion

Find the Ah Rating

Locate the ampere-hour capacity on your battery. Smartphone batteries are typically 3-5Ah (3000-5000mAh), laptop batteries 50-100Wh, and car batteries 45-80Ah.

Determine the Voltage

Find the nominal voltage. Lithium-ion cells are 3.7V nominal, lead-acid cells are 2V (12V for 6-cell), and NiMH cells are 1.2V.

Calculate Watt-Hours

Multiply Ah × V to get Wh. A 5Ah battery at 3.7V = 18.5Wh. This represents the total energy the battery can theoretically deliver.

Apply to Runtime Calculations

Divide Wh by your device power consumption in watts to estimate runtime in hours. An 18.5Wh battery powering a 5W device lasts approximately 3.7 hours.

Why Ah to Wh Conversion Matters

Airline Battery Regulations

FAA and IATA limit lithium batteries to 100Wh for carry-on luggage without approval, and 160Wh with airline approval. Converting Ah to Wh determines if your battery is flight-compliant.

Device Runtime Estimation

Knowing battery energy in Wh allows you to calculate how long devices will operate. This is critical for field equipment, medical devices, and emergency backup systems.

Battery Replacement Compatibility

When replacing batteries, matching Wh ensures equivalent energy capacity. A replacement battery with the same Ah but different voltage will provide different energy and may not be compatible.

Energy Cost Calculations

Electricity is billed in kWh. Converting battery Wh to kWh (divide by 1000) helps calculate the cost to charge batteries and compare operating costs of battery-powered vs grid-powered equipment.

Electrical Safety Tips & Best Practices

mAh to Wh Conversion

For milliamp-hour ratings common on smartphone batteries, divide mAh by 1000 first to get Ah, then multiply by voltage. A 5000mAh 3.7V battery = 18.5Wh.

Check Battery Chemistry

Different chemistries have different nominal voltages per cell: Li-ion 3.7V, LiFePO4 3.2V, NiMH 1.2V, Lead-acid 2.0V. Using the wrong voltage gives incorrect Wh values.

Real-World Capacity Loss

Actual usable Wh is typically 80-95% of rated capacity due to internal resistance, voltage sag under load, and cut-off voltage limitations of the device.

Temperature Compensation

Battery capacity drops in extreme temperatures. Subtract 10-20% from calculated Wh for cold weather operation (below 0°C/32°F) when planning critical applications.

3.7V

7.4V

11.1V

12V

1 Ah

3.7 Wh

5 Wh

7.4 Wh

11.1 Wh

12 Wh

2 Ah

7.4 Wh

10 Wh

14.8 Wh

22.2 Wh

24 Wh

5 Ah

18.5 Wh

25 Wh

37 Wh

55.5 Wh

60 Wh

10 Ah

37 Wh

50 Wh

74 Wh

111 Wh

120 Wh

20 Ah

74 Wh

100 Wh

148 Wh

222 Wh

240 Wh

50 Ah

185 Wh

250 Wh

370 Wh

555 Wh

600 Wh

100 Ah

370 Wh

500 Wh

740 Wh

1110 Wh

1200 Wh

200 Ah

740 Wh

1000 Wh

1480 Wh

2220 Wh

2400 Wh