Convert Between Ah, Wh, and Watts

Part 1. Understanding battery units

Ampere-Hour (Ah) – Represents a battery’s storage capacity. It indicates how much current a battery can supply over a set period. A 10Ah battery could deliver 10 amps for one hour, 5 amps for two hours, or 1 amp for ten hours, depending on the discharge rate. In practice, factors such as temperature, battery age, and discharge speed can slightly reduce the actual capacity.

Watt-Hour (Wh) – Measures total energy. While Ah tells you “how much current,” Wh tells you “how much energy” is stored. This is especially useful for comparing batteries with different voltages, since Wh normalizes capacity into an energy figure.

Watts (W) – Indicates power, the rate at which energy is used or generated. A device rated at 100W will consume 100Wh per hour of operation.

Milliampere-Hour (mAh) – Commonly used for smaller devices such as smartphones, drones, and cameras. 1Ah = 1,000mAh.

Kilowatt-Hour (kWh) – Equal to 1,000Wh. This is the standard unit on electricity bills and is also used to rate large battery systems, such as home energy storage or electric vehicle packs.

Part 2. The relationship between Ah, Wh, and Watts

Voltage is the critical link between these units. Without voltage, you cannot accurately convert Ah to Wh or Watts.

Key relationships:

• Wh = Ah × Volts

• Ah = Wh ÷ Volts

• Watts = Volts × Amps

• mAh to Wh: Wh = (mAh ÷ 1,000) × Volts

Example: A 12V, 100Ah battery: Wh = 100 × 12 = 1,200Wh (or 1.2kWh)

If you run a 100W device on this battery: Runtime ≈ 1,200Wh ÷ 100W = 12 hours (excluding efficiency losses).

Tip: Always use the nominal voltage of the battery, not the peak or charging voltage, for accurate conversions.

Part 3. Converting Ampere-Hours to Watts

This conversion is useful when you know a battery’s capacity in Ah and its voltage, but you want to estimate how much power it can provide over a certain time.

Formula: Watts = Ah × Volts ÷ Hours (when runtime is specified) For a 1-hour runtime: Watts = Ah × Volts

Example 1: 12V, 5Ah battery: Watts = 5 × 12 = 60W

Example 2: 24V, 10Ah battery discharged over 2 hours: Watts = (10 × 24) ÷ 2 = 120W

Quick Reference Table – Ah to Watts (1-hour runtime)

Professional tip: Use this calculation to check whether your inverter and battery combination can power a given load without overloading.

Part 4. Converting Ampere-Hours to Watt-Hours

This is one of the most common battery calculations, especially for comparing batteries with different voltages.

Formula: Wh = Ah × Volts

Example: A 24V, 200Ah battery: Wh = 200 × 24 = 4,800Wh (4.8kWh)

Tip: Watt-hours allow direct comparison between, for example, a 12V battery bank and a 24V battery bank. Without converting to Wh, two batteries with the same Ah but different voltages might appear equal in capacity, but their total stored energy can differ significantly.

Part 5. Converting Watt-Hours to Ampere-Hours

If you know the total energy capacity but need the current capacity, this conversion is essential for system sizing.

Formula: Ah = Wh ÷ Volts

Example: A 1,200Wh battery at 12V: Ah = 1,200 ÷ 12 = 100Ah

This is especially useful when purchasing battery packs for solar systems, as many manufacturers list only the Wh rating.

Part 6. Converting mAh to Wh

Small electronics often use mAh ratings, but airline regulations and energy audits often require Wh values.

Formula: Wh = (mAh ÷ 1,000) × Volts

Example: A 5,000mAh phone battery at 3.7V: Wh = (5,000 ÷ 1,000) × 3.7 = 18.5Wh

Reverse formula: mAh = (Wh ÷ Volts) × 1,000

Tip: For safety checks before air travel, confirm the Wh rating is under the airline limit (usually 100Wh).

Part 7. Converting Watts to Ampere-Hours

This calculation helps determine the size of a battery needed to run a device of known wattage for a specific time.

Formula: Ah = (Watts × Hours) ÷ Volts

Example: A 60W light for 5 hours on a 12V battery: Ah = (60 × 5) ÷ 12 = 25Ah

You can also reverse this to find how long a battery will last given its Ah rating: Hours = (Ah × Volts) ÷ Watts

Part 8. Kilowatt-hour conversions

For large systems, such as home backup batteries, electric vehicles, or industrial energy storage, kWh is the preferred unit.

Formulas:

• kWh = (Ah × Volts) ÷ 1,000

• Ah = (kWh × 1,000) ÷ Volts

Example: A 48V, 200Ah battery: kWh = (200 × 48) ÷ 1,000 = 9.6kWh

Tip: Converting to kWh allows you to easily compare your battery storage with your monthly electricity usage from your utility bill.

Part 9. Common mistakes to avoid

• Ignoring voltage – Ah and Wh cannot be converted directly without it.

• Mixing Watts and Watt-hours – Power vs. total energy is a frequent point of confusion.

• Confusing mAh with Ah – 1Ah equals 1,000mAh.

• Not accounting for efficiency losses – Real-world systems may lose 10–20% of stored energy.

• Assuming 1-hour discharge – Runtime affects the Ah-to-Watt relationship.

Part 10. FAQs