Wh to Ah Calculator

Convert Wh to Ah

Use this Wh to Ah Calculator to convert watt-hours into amp-hours at a selected battery voltage. Watt-hours measure stored energy, while amp-hours describe battery charge capacity at a specific voltage. This conversion is useful when you already know how much energy your system needs in Wh or kWh and you want to choose a battery size in Ah.

The conversion formula is simple: Ah = Wh ÷ Voltage. For example, 1200Wh divided by 12V equals 100Ah. The same 1200Wh divided by 24V equals 50Ah, and 1200Wh divided by 48V equals 25Ah. The energy is the same in all three examples, but the Ah number changes because the voltage changes.

This calculator is designed for battery planning, solar system sizing, inverter backup estimates, power station comparisons, RV battery banks, marine electrical systems, telecom backup systems, and lithium battery pack design. It is especially helpful when load studies, appliances, solar calculators, or electricity bills show energy in watt-hours or kilowatt-hours, but battery listings show capacity in amp-hours.

Wh to Ah Conversion Formula

The standard formula for converting watt-hours to amp-hours is:

Ah = Wh ÷ Voltage

For example, 1200 Wh ÷ 12V = 100 Ah. A 4800Wh battery bank at 48V is calculated as 4800 ÷ 48 = 100Ah. The formula works for lithium batteries, lead-acid batteries, power stations, solar battery banks, e-bike packs, marine battery systems, telecom backup batteries, and any other DC battery system as long as you use the correct nominal voltage.

Watt-hours are a unit of energy. Amp-hours are a unit of charge. A watt-hour rating tells you how much energy is stored or required. An amp-hour rating tells you how many amps a battery can theoretically deliver for a certain number of hours at its rated voltage. Because voltage is part of power and energy, you cannot accurately convert Wh to Ah without voltage. The voltage is not optional; it is the link between energy and charge capacity.

When you divide energy by voltage, you get the amp-hour capacity needed to store or deliver that amount of energy. If your target is 2400Wh and your system voltage is 24V, the result is 100Ah. If your target is 2400Wh and your system voltage is 12V, the result is 200Ah. The 12V system needs twice the Ah rating because it operates at half the voltage. This is why battery capacity comparisons should always include voltage.

Common Wh to Ah Conversions

Here are several quick reference conversions for popular battery system voltages. These examples use nominal voltage and do not include depth of discharge, inverter efficiency, cable losses, temperature effects, battery age, or reserve capacity.

• 1200 Wh @ 12V = 100 Ah
• 2400 Wh @ 24V = 100 Ah
• 4800 Wh @ 48V = 100 Ah
• 5120 Wh @ 51.2V = 100 Ah
• 5000 Wh @ 48V = 104.2 Ah
• 10000 Wh @ 48V = 208.3 Ah
• 10000 Wh @ 51.2V = 195.3 Ah
• 20000 Wh @ 48V = 416.7 Ah

These examples show how strongly voltage affects the Ah result. A 4800Wh storage target requires about 400Ah at 12V, 200Ah at 24V, or 100Ah at 48V. The stored energy is still 4800Wh, but the current and amp-hour ratings change because the electrical pressure of the system is different. For high-power solar and inverter systems, this is one reason 48V and 51.2V battery banks are common.

Understanding Watt-hours, Amp-hours, and Voltage

Watt-hours describe how much energy is available. If a battery is rated at 1200Wh, it can theoretically provide 1200 watts for one hour, 600 watts for two hours, 100 watts for twelve hours, or 50 watts for twenty-four hours before losses and discharge limits are considered. This makes Wh a practical unit for runtime and energy planning because most loads are rated in watts.

Amp-hours describe electric charge capacity. A 100Ah battery can theoretically deliver 100 amps for one hour or 10 amps for ten hours under ideal conditions. However, Ah by itself does not tell the whole energy story because it does not include voltage. A 100Ah battery at 12V has about 1200Wh, while a 100Ah battery at 48V has about 4800Wh. Both have the same Ah rating, but one stores four times more energy.

Voltage is the multiplier or divisor that connects these units. To go from Ah to Wh, multiply by voltage. To go from Wh to Ah, divide by voltage. When you understand this relationship, battery specifications become easier to compare. You can translate a load estimate in Wh into battery Ah, or translate a battery Ah rating into usable energy for runtime planning.

For lithium batteries, always use nominal voltage for general energy calculations unless the manufacturer provides a more specific energy rating. A single LiFePO4 cell is commonly calculated at 3.2V nominal. A single Li-ion or LiPo cell is commonly calculated at 3.7V nominal. Complete packs may be listed as 12V, 24V, 48V, or 51.2V depending on chemistry and series cell count. The printed battery label or datasheet should be the final reference.

Why Voltage Changes the Ah Result

Many beginners expect a Wh to Ah conversion to produce one fixed answer, but the answer depends completely on voltage. The reason is simple: higher voltage systems carry the same amount of power with less current. Since amp-hours are related to current over time, a higher voltage battery bank needs fewer amp-hours to store the same watt-hours of energy.

Imagine that your system needs 4800Wh of nominal storage. At 12V, the required capacity is 4800 ÷ 12 = 400Ah. At 24V, it is 4800 ÷ 24 = 200Ah. At 48V, it is 4800 ÷ 48 = 100Ah. The energy target does not change, but the Ah rating is lower at higher voltage. This is not because the higher-voltage battery is weaker. It is because each amp-hour at a higher voltage contains more energy.

This relationship also affects system wiring. A high-power inverter connected to a 12V battery bank draws much more current than the same inverter connected to a 48V bank. Higher current requires larger cables, stronger fuses, more careful voltage drop planning, and stronger busbars. Higher-voltage systems often reduce current, heat, and wiring cost for larger installations. The Wh to Ah calculator helps you see that difference clearly during the first planning stage.

Using Wh to Ah for Solar Battery Sizing

Solar system planning usually starts with energy use. You list each load, estimate its wattage, estimate how many hours it runs per day, and calculate daily watt-hours. For example, a 100W refrigerator running the equivalent of 10 hours per day uses about 1000Wh per day. A 50W fan running 8 hours uses 400Wh. A 20W lighting load running 5 hours uses 100Wh. Add all loads together to estimate daily energy demand.

After you know the daily Wh target, you can convert it to battery Ah at the chosen voltage. If your daily requirement is 2400Wh and you are building a 24V system, the nominal capacity is 2400 ÷ 24 = 100Ah. If the same system is 12V, the nominal capacity is 200Ah. If it is 48V, the nominal capacity is 50Ah. This conversion gives a starting point before you add safety margin.

Real solar battery sizing should include depth of discharge, inverter efficiency, charge controller losses, weather reserve, and aging. If you need 2400Wh of usable energy from a lithium battery and you plan to use only 80% of the battery capacity, the nominal storage target becomes 2400 ÷ 0.80 = 3000Wh. At 24V, that is 125Ah. If an inverter is involved and you estimate 90% efficiency, the required battery energy becomes even higher. This is why a simple Wh to Ah conversion is the first step, not the final engineering design.

Using Wh to Ah for RV, Marine, and Backup Power

RV and marine electrical systems often combine 12V DC loads with inverter-powered AC loads. Lights, fans, pumps, control boards, USB chargers, radios, and some refrigerators may run directly from DC. Laptops, microwave ovens, induction cookers, power tools, and household appliances often run through an inverter. When you calculate energy in watt-hours first, you can combine all of these loads into one daily energy number.

Once the total Wh is known, this calculator helps you choose a battery bank in Ah. A small camper that needs 1200Wh per day could use about 100Ah at 12V before losses and reserve. A larger RV needing 5000Wh per day would require about 416.7Ah at 12V, 208.3Ah at 24V, or 104.2Ah at 48V before adjustments. That comparison helps show when a higher-voltage architecture may be more practical.

Backup power systems use the same logic. If you want to keep essential loads running during an outage, list the watts and runtime of each critical load. A 60W internet system for 10 hours uses 600Wh. A 120W refrigerator average load for 12 hours uses 1440Wh. A 40W lighting and phone charging group for 8 hours uses 320Wh. Together, those loads require 2360Wh before losses. At 24V, that is about 98.3Ah nominal; at 48V, it is about 49.2Ah nominal.

Depth of Discharge and Usable Capacity

The Wh to Ah formula gives nominal capacity. Nominal capacity is the energy rating before you decide how much of the battery you will actually use. Depth of discharge, often shortened to DoD, describes the percentage of the battery capacity that is discharged. A battery used to 80% DoD has 20% remaining reserve. A battery used to 50% DoD has half its capacity left.

Lithium batteries often allow deeper discharge than lead-acid batteries, but the recommended limit still depends on the manufacturer, chemistry, BMS, warranty, temperature, and cycle life goal. If your load requires 4000Wh of usable energy and you want to discharge the battery only 80%, divide the usable energy by 0.80. The battery should have about 5000Wh nominal capacity. At 48V, that is 5000 ÷ 48 = 104.2Ah.

Inverter efficiency also changes the usable result. If an inverter is 90% efficient, a 1000Wh AC load may require about 1111Wh from the battery. If you also limit depth of discharge to 80%, the nominal battery target becomes 1111 ÷ 0.80 = 1388.75Wh. At 12V, that is about 115.7Ah. This example shows why real-world battery banks often need to be larger than the simple load energy calculation suggests.

Series and Parallel Battery Banks

Battery bank configuration affects voltage and Ah. Connecting batteries in series increases voltage while the Ah rating stays the same. For example, four 12V 100Ah batteries connected in series create a 48V 100Ah bank. The energy is 48 × 100 = 4800Wh. Connecting batteries in parallel increases Ah while voltage stays the same. Four 12V 100Ah batteries in parallel create a 12V 400Ah bank, which is also 4800Wh.

Both examples store the same nominal energy, but they behave differently electrically. The 48V bank delivers the same power with much lower current than the 12V bank. That can reduce cable size, voltage drop, heat, and stress on connectors. However, every device in the system must be compatible with the selected battery voltage. Inverters, DC-DC converters, charge controllers, fuses, breakers, monitoring equipment, and chargers must all match the system design.

When using this calculator, enter the voltage of the complete battery bank, not the voltage of one battery unless you are calculating one battery by itself. If you have a 48V bank made from multiple batteries, enter 48V or the exact nominal voltage specified by the manufacturer. If you have a 51.2V LiFePO4 server-rack battery, entering 51.2V gives a more accurate Ah result than entering 48V.

Practical Wh to Ah Examples

Example 1: 1200Wh at 12V. The formula is 1200 ÷ 12 = 100Ah. This is a common size for a small 12V lithium battery bank, portable solar setup, or light backup power system. Real usable runtime depends on inverter losses, allowable depth of discharge, and the load profile.

Example 2: 4800Wh at 48V. The formula is 4800 ÷ 48 = 100Ah. This is a common way to understand a 48V class solar battery. If the battery is actually a 51.2V LiFePO4 pack, 5120Wh ÷ 51.2V = 100Ah. Both numbers may appear in product descriptions depending on whether the seller uses system class voltage or exact nominal voltage.

Example 3: 5000Wh at 48V. The formula is 5000 ÷ 48 = 104.2Ah. This is close to the capacity of many home energy storage modules. If the design requires 5000Wh usable rather than nominal, you should increase the battery size to account for DoD and efficiency.

Example 4: 10000Wh at 48V. The formula is 10000 ÷ 48 = 208.3Ah. A 10kWh target is common in larger solar and backup systems. At 12V, the same energy would require about 833.3Ah, which shows why larger systems usually move away from 12V battery banks.

Common Mistakes to Avoid

• Forgetting voltage: Wh cannot be converted to Ah without voltage. A 1200Wh target is 100Ah at 12V, 50Ah at 24V, and 25Ah at 48V.
• Using charge voltage instead of nominal voltage: General energy calculations normally use nominal voltage, not maximum charging voltage or fully charged voltage.
• Ignoring usable capacity: The simple formula gives nominal Ah. Real designs should include depth of discharge, reserve capacity, and system losses.
• Comparing Ah across different voltages: A 100Ah 12V battery and a 100Ah 48V battery do not store the same energy. Convert both to Wh for a fair comparison.
• Confusing W and Wh: Watts are power at an instant. Watt-hours are energy over time. A 100W load running for 10 hours uses 1000Wh.
• Overlooking discharge current: A battery may have enough Ah but still be unable to safely supply a high-power inverter. Check BMS and continuous discharge ratings.

Battery Capacity Planning Checklist

Start by listing every load you want to power. Write down the wattage of each load and the number of hours it runs per day. Multiply watts by hours for each item, then add the results to get total daily watt-hours. If you are sizing backup power, also decide how many hours or days of autonomy you want. A system intended to cover a short outage may need far less energy than a system designed for multiple cloudy days.

Next, choose a system voltage. Small portable systems may be simple at 12V. Medium RV, marine, and cabin systems may use 24V. Larger inverter and solar storage systems often use 48V or 51.2V. Use the Wh to Ah calculator to translate your energy target into battery capacity at each voltage. This helps you compare battery bank options before choosing equipment.

Then adjust for real-world limits. Add margin for depth of discharge, inverter efficiency, wiring losses, battery aging, cold temperature performance, future load growth, and emergency reserve. Finally, check datasheets. Confirm nominal voltage, rated Ah, rated Wh, maximum continuous discharge current, peak current, charge voltage, operating temperature, recommended charging profile, communication features, and warranty conditions. The calculator gives a fast estimate, but manufacturer data should guide final decisions.

Related Tools

Use these related calculators to continue your battery planning workflow:

• Battery Ah to Wh Calculator
• Battery Capacity Calculator
• Solar Battery Calculator
• Battery Runtime Calculator
• mAh to Wh Calculator