Battery Conversion Calculator
All Battery Capacity Conversion Formulas in One Place
Watt Hours, Amp Hours & mAh Explained
Watt Hours (Wh) measure total energy storage — how much work a battery can do. Amp Hours (Ah) measure charge capacity at a specific voltage. Milliamp Hours (mAh) are Ah × 1000, used for smaller batteries. The relationships: Wh = Ah × V, Ah = Wh ÷ V, mAh = Ah × 1000. For individual converters, see Wh to Ah or Wh to mAh.
Energy vs Power Differences
Energy (Wh) and power (W) are often confused. Power is the rate of energy use: Watts = Joules/second. Energy is power over time: Wh = W × hours. A 100W lightbulb running for 10 hours uses 1,000Wh (1kWh). A 1000W microwave running for 6 minutes uses 100Wh. See our microwave watt converter for power calculations.
Online Conversion Calculator Accuracy
Our battery conversion calculator uses IEEE-standard floating point arithmetic for maximum precision. All calculations happen in your browser — no server round-trips that could introduce latency or errors. Results are displayed to 4 decimal places for engineering-grade accuracy.
Real-World Battery System Examples
Solar Storage System Sizing
A household consuming 30kWh/day with 2 days of autonomy needs 60kWh of storage. At 48V, that requires 1,250Ah of battery capacity. With 80% depth of discharge for lithium, you need 1,562Ah nameplate capacity — typically eight 200Ah 48V batteries.
EV Battery Pack Comparison
Tesla Model 3 Long Range: 75kWh at ~350V = 214Ah. Nissan Leaf: 40kWh at ~350V = 114Ah. Rivian R1T: 135kWh at ~400V = 337Ah. Converting between Wh and Ah allows direct comparison of battery packs across different voltage architectures.
Emergency Backup Power Systems
A UPS with a 12V 100Ah battery provides 1,200Wh. At 500W load, runtime = 1,200 ÷ 500 = 2.4 hours (theoretical). With 85% inverter efficiency, actual runtime ≈ 2.04 hours. For detailed runtime calculations, see Ah to Wh converter.
Choosing the Right Engineering Conversion Tool
When to Use Wh vs Ah
Use Wh when comparing batteries at different voltages, calculating energy costs, or checking airline regulations. Use Ah when sizing charge controllers, calculating charging times, or comparing batteries at the same voltage. Use mAh for portable electronics and small devices.
Metric to Imperial Conversion in Energy Systems
While Wh and Ah are universal, some legacy systems use BTU (British Thermal Units): 1 Wh = 3.412 BTU. Horsepower-hours are another imperial energy unit: 1 hp·h = 746 Wh. Our tools focus on the SI-derived units most commonly used in modern battery engineering. For broader unit conversions, see our chemical unit conversion guide.