Amp Hours to Watt Hours Calculator

Converting amp hours to watt hours is straightforward with this simple formula: Wh = Ah x V (watt hours equals amp hours multiplied by voltage). This calculation tells you the total energy capacity of your battery in a universally comparable unit.

Example 1: A 100Ah battery at 12 volts contains 100 x 12 = 1,200 watt hours. This is enough energy to run a 100-watt device for 12 hours (before accounting for inverter losses and depth of discharge limits).

Example 2: A 200Ah LiFePO4 battery at 12.8V nominal voltage contains 200 x 12.8 = 2,560 watt hours. With 80% usable capacity, that gives you 2,048Wh of practical energy storage.

The reverse formula is equally useful: Ah = Wh / V. If you know you need 2,000Wh of storage and have a 24V system, you need 2,000 / 24 = 83.3Ah of battery capacity.

When planning an off-grid solar system, RV electrical setup, or backup power solution, watt hours are the most practical unit for sizing your battery bank. While amp hours tell you about raw battery capacity, watt hours tell you how much actual work that energy can perform.

Device matching: Most appliances are rated in watts, not amps. A 60W laptop, a 100W mini fridge, or a 1,500W microwave - these ratings make it easy to calculate runtime when you know your battery capacity in watt hours.

System comparison: When comparing a 200Ah 12V battery to a 100Ah 24V battery, the amp hour numbers are misleading. Both actually store 2,400Wh of energy - they are equivalent in practical terms.

Cost per Wh: Smart shoppers compare batteries by their cost per watt hour, not cost per amp hour. This levels the playing field across different voltages and capacities, helping you find the best value for your energy storage needs.

When designing a battery system, voltage choice significantly impacts performance, cost, and practicality. Understanding how amp hours translate to watt hours at different voltages helps you make the right choice for your application.

12V systems are the most common for RVs, boats, and small off-grid setups. A 100Ah 12V battery provides 1,280Wh (LiFePO4). The advantage is compatibility with automotive accessories and widespread charger availability. The downside is high current draw - a 2,000W load pulls 167 amps, requiring heavy gauge wiring.

24V systems cut current in half for the same power output. That same 2,000W load draws only 83 amps. This means smaller, cheaper wiring and lower losses over distance. A 100Ah 24V battery stores 2,560Wh - double the energy of a 100Ah 12V battery. Ideal for medium-sized off-grid cabins and larger RVs.

48V systems are the standard for whole-home backup and large solar installations. Current is reduced to one-quarter of 12V systems, minimizing wire costs and energy losses. A 100Ah 48V battery stores 5,120Wh. Most grid-tie inverters and serious off-grid equipment operate at 48V.

Understanding Ah to Wh conversion becomes practical when applied to real batteries and devices you might encounter. Here are common scenarios where this calculation proves essential.

Power station batteries: Popular portable power stations like the Jackery 1000 or EcoFlow Delta are rated in watt hours (1,002Wh and 1,260Wh respectively). At 12V equivalent, these would be roughly 83Ah and 105Ah. When comparing to traditional 12V batteries, watt hours provide the clearer picture.

Electric bike batteries: An e-bike with a 48V 13Ah battery contains 624Wh of energy. A larger 52V 17.5Ah pack contains 910Wh. These numbers help you estimate range and compare different bike battery options directly.

RV house batteries: A common RV setup with two 100Ah 12V LiFePO4 batteries in parallel provides 2,560Wh total (200Ah x 12.8V). With 80% depth of discharge, you have 2,048Wh usable - enough to run a 50W fridge for 40+ hours.

Off-grid cabin: A 48V system with four 100Ah batteries (wired as 2S2P) provides 10,240Wh. At a daily consumption of 5,000Wh, this gives you about 1.6 days of autonomy after accounting for 80% usable capacity.

Even experienced off-gridders make errors when converting between amp hours and watt hours. Avoiding these common mistakes ensures accurate system sizing and realistic runtime expectations.

Using nominal vs actual voltage: A "12V" LiFePO4 battery actually operates at 12.8V nominal (ranging from 10V to 14.6V during discharge and charge). Using 12V instead of 12.8V underestimates capacity by 6.7%. For a 200Ah battery, that is 160Wh of "missing" energy in your calculations.

Ignoring depth of discharge: Total watt hours are not usable watt hours. LiFePO4 batteries can safely use 80-90% of capacity, while lead acid should only use 50%. A 1,200Wh lead acid battery only provides 600Wh of practical use - the same as a 750Wh LiFePO4 battery.

Forgetting inverter losses: When powering AC devices from a DC battery, inverter efficiency matters. A 90% efficient inverter means 10% of your watt hours become heat. Plan for this by dividing your needs by inverter efficiency: 1,000Wh needed / 0.90 = 1,111Wh from the battery.

Mixing series and parallel math: Batteries in series add voltage but not amp hours: two 12V 100Ah batteries in series create 24V at 100Ah (2,400Wh). In parallel, they add amp hours: two 12V 100Ah in parallel create 12V at 200Ah (2,400Wh). The total watt hours are the same, but the amp hour rating is not.

Amp hours (Ah) measure electric charge capacity - specifically, how many coulombs of charge a battery can store. A 100Ah battery can deliver 100 amps for 1 hour, 50 amps for 2 hours, or 10 amps for 10 hours (approximately, as Peukert effect impacts high discharge rates).

Watt hours (Wh) measure energy capacity - the actual work the battery can perform. This accounts for both charge (amp hours) and electrical pressure (voltage), giving you a complete picture of energy storage. One watt hour equals one watt of power used for one hour.

Think of it like water storage: amp hours are like gallons of water, while watt hours are like the potential energy of that water. A tank on a hill (higher voltage) has more useful energy than the same water at ground level. The formula Wh = Ah x V captures this relationship.

For practical battery comparison and runtime calculations, watt hours are almost always more useful. They let you directly compare batteries of different voltages and calculate exactly how long devices will run - making system design much more straightforward.