How to Use Our Ah to Wh Converter
To find the total energy stored in your battery, you only need two values, which are almost always printed on the battery’s label or case.
-
Battery Capacity (in Ah): Enter the capacity of your battery in amp-hours. This is a common rating for car, RV, marine, and other deep-cycle batteries (e.g., 50Ah, 100Ah).
-
Voltage (in Volts): Enter the nominal voltage (V) of your battery. This is a critical value, often 12V, 24V, or 48V for larger battery systems.
Once both values are entered, the calculator will immediately display the total energy capacity in Watt-hours (Wh).
Understanding Your Results
The result from the calculator is your battery’s capacity in Watt-hours (Wh). This number represents the total amount of energy the battery can store and is the universal standard for comparing battery capacities.
Here’s a breakdown of the components to help you understand what the result means:
-
Amp-hour (Ah): Think of amp-hours as the size of the fuel tank. It measures electric charge and tells you how much current the battery can provide over a period of time. A 100 Ah battery can, for example, deliver 5 amps for 20 hours.
-
Voltage (V): Think of voltage as the pressure of the fuel. It’s the electrical force that pushes the energy out of the battery. A higher voltage system can deliver power more efficiently.
-
Watt-hour (Wh): This is the true measure of total energy. It’s the combination of the fuel tank’s size (Ah) and the fuel’s pressure (V). It answers the question, “How much total work can this battery perform?”
The formula used by the calculator is beautifully simple: Watt-hours (Wh) = Amp-hours (Ah) × Voltage (V)
Why Watt-Hours are the Gold Standard
Comparing two batteries by amp-hours alone is misleading if their voltages are different. A battery with a lower Ah rating but a higher voltage can hold significantly more energy.
Look at the two 100 Ah batteries in the table. The 48V battery holds four times more energy than the 12V battery, despite having the same amp-hour rating. This is why you must convert to watt-hours to understand a battery’s true potential.
Frequently Asked Questions
Why do airlines use Watt-hours (Wh) instead of Amp-hours (Ah)?
Airlines use Watt-hours (Wh) because it is a universal measure of total energy. As shown in the table above, an “amp-hour” is meaningless without its corresponding voltage. A 100 Ah battery could be a relatively small 1,200 Wh battery or a massive 4,800 Wh battery.
Since safety regulations are based on the total potential energy that could be released in a fire, Watt-hours (Wh) is the only reliable metric. It puts all batteries, regardless of their voltage or Ah rating, on a level playing field.
Is a 100Ah battery allowed on a plane?
This is a very common question, and the answer is: it depends entirely on the voltage.
Airline regulations (per the FAA) for lithium-ion batteries are:
-
Up to 100 Wh: Allowed in carry-on. No specific limit on quantity for personal use.
-
101-160 Wh: Allowed in carry-on, but limited to two batteries per person, and requires airline approval before flying.
-
Over 160 Wh: Forbidden on passenger aircraft.
Let’s apply this to a 100Ah battery:
-
A 100 Ah 12V battery is 100 × 12 = 1,200 Wh. This is far over the 160 Wh limit and is strictly forbidden.
-
A 100 Ah 3.7V battery (which doesn’t really exist at this capacity as a single cell) would be 100 × 3.7 = 370 Wh. Still forbidden.
In general, any battery with a capacity measured in Amp-hours (like car, RV, or marine batteries) is far too large to be taken on a passenger plane. The airline limits are designed for consumer electronics like laptops, cameras, and USB power banks (which are typically rated in mAh).
What’s the difference between Ah and Wh again?
Think of it like this:
-
Ah (Amp-hours) tells you how long a battery can sustain a certain current draw. It’s about endurance at a specific pace.
-
Wh (Watt-hours) tells you the total energy available to do work. It’s about the total potential.
Wh is the better metric for comparing the overall capacity of two different batteries.
How many watt-hours is a 100Ah 12V battery?
This is a benchmark calculation for many RV and boat owners. 100 Ah × 12V = 1,200 Wh This can also be expressed as 1.2 kilowatt-hours (kWh).
Can I compare a 200Ah 12V battery to a 100Ah 24V battery?
Yes, and this is a perfect use case for our calculator. On the surface, it’s hard to tell which one is “bigger.” Let’s convert both to Watt-hours.
-
Battery A: 200 Ah × 12V = 2,400 Wh
-
Battery B: 100 Ah × 24V = 2,400 Wh
As it turns out, both batteries store the exact same amount of total energy. The 24V system (Battery B) can deliver that energy more efficiently with thinner cables, but the total reserve is identical.
What does “nominal voltage” mean for my battery?
The “nominal voltage” is the standard, “named” voltage of a battery, like 12V or 24V. The actual, measured voltage will change as the battery is used. A fully charged 12V lead-acid battery might measure 12.7V or higher, and it might drop to 12.0V or lower as it’s discharged. The nominal voltage is the average or reference voltage used for all standard calculations.
How does the Ah rating relate to how long my battery will last?
You can estimate runtime with a simple formula: Runtime (in hours) = Battery Amp-hours (Ah) / Appliance Amp Draw (A)
Concrete Example: You have a 100 Ah battery and want to run a small fridge that draws 4 amps. Runtime = 100 Ah / 4 A = 25 hours Important Note: This is a theoretical maximum. Real-world runtime is often less due to temperature, battery age, and the fact that you should not fully drain a deep-cycle battery (a 50% depth-of-discharge is common).
How can I find the voltage of my battery?
The voltage is almost always clearly printed on the battery’s label or sticker. It’s one of the most important specifications. Look for a number followed by “V”, such as “12V” or “24V”. If you can’t find it, check the product’s technical manual or the manufacturer’s website.
Does a higher Wh rating mean a better battery?
For a given battery chemistry and size, a higher Wh rating means it stores more energy and will generally provide a longer runtime. Therefore, when comparing two batteries, the one with the higher Wh rating is “bigger” in terms of energy capacity. However, “better” can also include factors like lifespan (charge cycles), weight, size, and cost.
What is the difference between Ah and mAh?
mAh stands for milliamp-hour. The prefix “milli-” means one-thousandth.
Ah is used for large batteries (cars, solar systems). mAh is used for small consumer electronics like smartphones (e.g., 5,000 mAh) and power banks. To convert mAh to Ah, simply divide by 1,000.
Now that you’ve converted your battery’s capacity to watt-hours, you might want to estimate its runtime with specific appliances. Visit our Battery Life Calculator for detailed calculations. If you are starting with a larger energy value, like from a home solar system, use our kWh to Ah Converter.
