Amp Hour Calculator / Battery Capacity Calculator

Use this amp hour calculator and battery capacity calculator to convert mAh, Ah, Wh, and kWh, estimate usable battery capacity, and compare battery bank sizes for home backup, RV, marine, off-grid, and solar generator setups.

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How to Calculate Amp Hours

Amp hours (Ah) tell you how much current a battery can deliver over time. In simple terms, a higher amp hour rating usually means more stored battery capacity.

One of the most common battery formulas is: Ah = Wh ÷ V

The Delta 3 Max has a 2048Wh battery, so see the example below converting to amp hours.

Example: if a battery stores 2,048Wh and operates at 51.2V, then: 2,048 ÷ 51.2 = 40Ah

Battery Capacity Formulas

• Ah = Wh ÷ V
• Wh = Ah × V
• mAh = Ah × 1,000
• kWh = Wh ÷ 1,000

What Battery Type Means for Usable Capacity

Not every battery chemistry is meant to be discharged the same amount. Lithium batteries are commonly used deeper than lead acid batteries, which means two batteries with the same rated capacity may not have the same practical usable energy.

This battery capacity calculator includes an optional usable-capacity estimate to help shoppers compare battery bank options for backup power, off-grid storage, RV power systems, marine batteries, and solar generator setups.

Common Battery Voltages

• 12V batteries for RVs, boats, and smaller backup systems
• 24V battery banks for larger off-grid systems
• 48V battery banks for whole-home backup and solar storage
• 51.2V lithium batteries common in LiFePO4 energy storage systems

Why Amp Hours Matter

Understanding amp hours helps you size a battery bank correctly, compare lithium and lead acid options, and estimate runtime for appliances, lights, electronics, pumps, and emergency backup loads.

Frequently Asked Questions

How do I convert watt hours to amp hours?

Divide watt hours by battery voltage. Example: 1,200Wh ÷ 12V = 100Ah.

How do I convert amp hours to watt hours?

Multiply amp hours by battery voltage. Example: 200Ah × 12V = 2,400Wh.

What is the difference between Ah and mAh?

1Ah equals 1,000mAh. Milliamp hours are usually used for smaller batteries and devices.

Why is usable battery capacity lower than rated capacity?

Some battery types should not be fully discharged in normal use. That is why practical usable energy can be lower than the full rated battery capacity.