Battery Watt-Hours Calculator

Why Watt-Hours Matter

Milliamp-hours (mAh) and amp-hours (Ah) measure charge, not energy. Two batteries can have the same Ah rating but very different energy storage if they operate at different voltages. Watt-hours (Wh) is the true measure of energy storage and lets you compare batteries of different voltages.

The Conversion Formula

Energy (Wh) = Voltage (V) × Capacity (Ah) or equivalently: Energy (Wh) = Voltage (V) × Capacity (mAh) / 1000

How to Use This Calculator

Enter the battery voltage and its capacity in mAh or Ah. The calculator outputs energy in Wh, and optionally calculates runtime at a given load power (W).

Practical Examples

Example 1: 3.7V 5,000 mAh smartphone battery → 3.7 × 5 = 18.5 Wh.

Example 2: 12V 100Ah car battery → 12 × 100 = 1,200 Wh = 1.2 kWh.

Example 3: 48V 20Ah e-bike battery → 48 × 20 = 960 Wh. Running a 250W motor at 80% efficiency: runtime = 960 × 0.8 / 250 = 3.07 hours of riding.

Common Applications

• Solar system sizing: Matching battery bank Wh to daily load and autonomy requirements.
• EV and e-bike range estimation: Wh per kilometre is the standard metric for EV efficiency.
• Portable power station comparison: Always compare Wh, not just Ah, when the voltage differs.
• Aviation and shipping: Regulations (e.g., IATA) restrict lithium battery transport by Wh.