Watt Hours to Amp Hours: Calculate and Compare

Understanding how to convert watt-hours (Wh) to amp-hours (Ah) is essential for battery sizing and performance evaluation in electric vehicles, energy storage systems, and portable electronics.

Wh and Ah describe the same energy in different ways. The key difference is that Wh includes voltage, while Ah does not. This makes conversion important when comparing batteries with different voltages.

In this guide, you will learn the core formulas, simple examples, and practical rules for Wh to Ah and Ah to Wh conversion, and how voltage affects all calculations.

Key takeaways

• Wh measures total energy, Ah measures charge capacity
• Conversion depends on voltage (V)
• Formula: Wh = V × Ah, Ah = Wh ÷ V
• Wh is better for comparing different battery systems
• Voltage is the key variable in all conversions

Part 1. What is a watt hour (wh)?

A watt-hour (Wh) is a unit of energy that shows how much power a battery can deliver over time.

Basic electrical relationship:
Power (W) = Voltage (V) × Current (A)
(Reference: IEC electrical standards)

Energy formula:
Wh = V × A × h

Example: Watt hours calculation

A device runs at 12V and draws 2A for 5 hours:

Wh = 12 × 2 × 5 = 120 Wh

So the system consumes 120 watt-hours of energy.

Part 2. What is an amp hour (ah)?

An amp-hour (Ah) measures how much electric charge a battery can deliver over time at a given voltage.

Formula
Ah = Wh ÷ V

Example

If a battery has 240 Wh at 12V:

Ah = 240 ÷ 12 = 20 Ah

This means the battery can deliver 20A for 1 hour (theoretical value).

Part 3. How to convert watt hours to amp hours (wh to ah)

To convert Wh to Ah, divide watt-hours by voltage.

Formula
Ah = Wh ÷ V

Example

A 250 Wh battery at 12V:

Ah = 250 ÷ 12 = 20.83 Ah

Part 4. How to convert amp hours to watt hours (ah to wh)

To convert Ah to Wh, multiply amp-hours by voltage.

Formula
Wh = Ah × V

Example

A 30Ah battery at 24V:

Wh = 30 × 24 = 720 Wh

Part 5. Why voltage matters in wh to ah conversion

Voltage determines how much energy is stored in a battery system.

Examples:

• 12V 100Ah = 1200Wh
• 24V 100Ah = 2400Wh

Even with the same Ah, higher voltage means more energy. This is why Wh is more accurate for comparing batteries across systems.

For faster and more accurate conversion, you can also use an online tool: Watt-hour to Amp-hour Calculator

Part 6. Battery selection guide: wh vs ah for battery sizing

When selecting a battery, do not rely only on amp-hour ratings.

Instead:

• Use Wh to evaluate total energy capacity
• Check voltage compatibility with your system
• Consider discharge rate (C-rate)
• Match runtime requirements with real energy demand
• Use Ah only for same-voltage comparisons

For engineering-level selection, Wh provides a more reliable basis for system design and energy planning.

Part 7. FAQs watt hours to amp hours (wh to ah)