How to Calculate Watt Hours (Wh) to Amp Hours (Ah) -Wh to Ah Conversion
How to Calculate Watt Hours (Wh) to Amp Hours (Ah) -Wh to Ah Conversion
When designing or selecting a battery system, you’ll often see capacity shown in Watt-hours (Wh) ou Ampere hour (Ah) (also written as ampere-hour). These units come from the International System of Units (SI) and are widely used to describe a battery’s storage capacity and its ability to support real-world energy consumption.
In this article, we’ll explain what Wh and Ah mean, how they relate to kilowatt hours (kWh), and how to convert Wh → Ah correctly based on voltage, battery type of battery, and your system’s power rating.
1) What Is Watt Hour (Wh)? Total Amount of Energy Stored
A Watt-hour (Wh) is a unit of energy. It represents the total amount of energy a battery can store (or deliver). In practical terms, Wh tells you how much energy can be used for generating or consuming electrical power over time.
Formula (Energy):
So if a battery has higher voltage or higher Ah, it usually has higher energy storage.
Wh vs kilowatt hours (kWh)
Large systems like home backup systems and power stations often use kilowatt hours (kWh):
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1 kWh = 1000 Wh
Example:
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2 kWh battery pack = 2000 Wh
kWh is commonly used for energy consumed (for example, electricity bills and system runtime estimates), and for comparing storage in power stations.
2) What Is Ampere Hour (Ah)? Battery’s Amp Hour Rating
An Ampere hour (Ah) is a unit of electric charge. It describes how much current a battery can deliver over time.
For instance:
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10Ah means the battery can theoretically provide 10A for 1 hour (or 1A for 10 hours)
This is why you’ll often hear people talk about a battery’s amp hour rating ou battery’s amp hour rating (Ah rating). In product specs it may appear as:
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Ah rating
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battery’s amp hour rating
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battery’s amp hour rating (Ah)
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battery’s amp hour rating / battery s amp hour rating (informal writing)
However, Ah alone doesn’t fully describe energy unless you also know the voltage. Two batteries can have the same Ah but very different total energy.
3) How to Convert Watt Hours to Amp Hours -Wh to Ah Conversion
To convert Watt-hours (Wh) to Amp-hours (Ah), you must know the battery’s nominal voltage.
Conversion Formula (Wh to Ah Conversion
This directly links energy (Wh) to charge capacity (Ah).
4) Wh to Ah Conversion Examples (Including Higher Power Loads)
Example A: 480Wh battery pack at 48V
So the battery’s amp hour rating is 10Ah (at 48V nominal).
Example B: 1200Wh battery at 12V
Example C: 2 kWh (2000Wh) power station at 24V
This example is common for power stations and energy storage modules that advertise in kWh.
5) How Power Rating and Energy Consumption Affect Runtime
Battery sizing is not only about converting units. You also need to consider:
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power rating (W): how many watts of power your load requires
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energy consumption (Wh or kWh): the energy used over time
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whether the device is generating or consuming power (e.g., charging from solar vs powering a load)
Quick runtime estimate (very practical)
If you know the load is 200W and your battery stores 600Wh:
If the load has higher power (for example 600W), then:
This demonstrates why a higher load power rating reduces runtime quickly—even if the battery’s ah rating seems large.
6) Why Voltage Matters: Same Wh, Different Ah Rating
Two batteries can store the same energy but have different Ah:
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12V × 100Ah = 1200Wh
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24V × 50Ah = 1200Wh
Same total amount of energy, different ampere hour capacity and current profile.
This matters in real applications because system wiring, BMS design, and inverter selection depend on voltage and current (Ah).
7) Type of Battery and Battery Performance Considerations
In real products, available energy is affected by:
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discharge rate (high current loads reduce usable capacity)
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temperature and aging
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BMS limits
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conversion losses (inverter efficiency)
So while Wh ↔ Ah formulas are correct, real-world battery performance and available storage capacity can vary. For high-current applications or higher power loads, the effective energy delivered can be lower than the theoretical Wh value.
8) Common Mistakes to Avoid
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❌ Converting Wh to Ah without voltage
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❌ Comparing Ah rating of different voltage batteries
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❌ Ignoring load power rating et energy consumed
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❌ Assuming bigger Ah always means more energy
When comparing batteries, Wh/kWh is best for overall energy; Ah helps when designing around current, wiring, and BMS limits.
Conclusion
To convert Wh to Ah accurately:
Ah = Wh ÷ V
Wh (or kilowatt hours kWh) tells you the total amount of energy stored, while Ah (or ampere hour) tells you the battery’s charge capacity and relates to current draw. For real projects—especially power storage et power stations—you should consider not only unit conversion but also load watts of power, system power rating, and real-world battery performance.
