Watt Hours to Amp Hours: How to Convert Wh to Ah
Converting watt hours (Wh) to amp hours (Ah) is the quickest way to match the battery to the gear you plan to run off-grid whether that’s a 12V caravan setup, a portable camping fridge or a 4WD dual-battery rig. Spec sheets tend to list the two as if they’re interchangeable but they measure different things. This guide explains the difference and works through both conversions with practical examples. From there, your appliance ratings give you the daily amp hours your battery has to supply for Australian touring and camping setups.
Quick Answer
Divide the watt hours by the system’s nominal voltage to get amp hours:
Ah = Wh ÷ V
For example, a 1,200Wh battery on a 12V system works out to:
1,200Wh ÷ 12V = 100Ah
Key Takeaways
Wh measures total electrical energy, or how much energy a power pack can supply over time regardless of the voltage.
Ah measures electric charge, but it cannot tell you the battery’s stored energy unless the nominal voltage is also known.
System voltage dictates the outcome: double the voltage from 12V to 24V and you halve the amp hours needed for the same watt-hour demand.
Real-world usable capacity is always lower than nominal rating: inverter losses, the Aussie heat and depth-of-discharge limits all take a cut.
What Is the Difference Between Wh and Ah?
Wh and Ah describe different aspects of battery capacity, and knowing the difference makes it easier to compare batteries and size up how much energy they can supply.
What Does Wh Measure?
Watt hours measure energy, and since watts account for both voltage and current, Wh lets you compare batteries with different voltages and chemistries. For appliance consumption rather than battery storage, converting watts to kWh also requires the operating time.
What Does Ah Measure?
Amp hours measure electric charge over time – 1Ah rating means a battery can supply 1 amp for an hour under specified conditions. Without the voltage, though, that figure doesn’t tell you how much energy the battery stores.
The Key Difference Between Energy and Electric Charge
Ah measures electric charge, while Wh measures energy. For the same amp-hour capacity, a higher nominal voltage means more stored energy. For example, a 100Ah battery at 12V stores 1,200Wh. Wire two identical batteries in series and the voltage doubles to 24V while the amp-hour capacity stays at 100Ah, giving a total of 2,400Wh.
How Do You Convert Watt Hours to Amp Hours?
To convert Wh to Ah, divide by the battery’s nominal voltage. To reverse the calculation, multiply amp hours by nominal voltage.
The Wh to Ah Conversion Formula
Divide the energy capacity in watt hours by the nominal voltage to get the equivalent capacity in amp hours:
Ah = Wh ÷ V
Where:
Ah = Capacity in Amp Hours
Wh = Energy in Watt Hours
V = Nominal Battery Voltage (Volts)
For example, a 1,200Wh battery on a 12V system has an equivalent capacity of:
1,200Wh ÷ 12V = 100Ah
How to Convert Amp Hours to Watt Hours (Ah to Wh)
If the label gives you amp hours and voltage but not watt hours, multiply the two – a watt is just a volt times an amp so that gives you the total stored energy:
Wh = Ah × V
For example, a 100Ah battery at 12V stores:
100Ah × 12V = 1,200Wh
The following table shows how to convert amp hours to watt hours for common battery capacities at different nominal voltages.
Battery Size (Ah) | Watt Hours at 12V | Watt Hours at 12.8V (LiFePO4) | Watt Hours at 24V |
|---|---|---|---|
50 Ah | 600 Wh | 640 Wh | 1,200 Wh |
100 Ah | 1,200 Wh | 1,280 Wh | 2,400 Wh |
150 Ah | 1,800 Wh | 1,920 Wh | 3,600 Wh |
200 Ah | 2,400 Wh | 2,560 Wh | 4,800 Wh |
300 Ah | 3,600 Wh | 3,840 Wh | 7,200 Wh |
Use the column matching your battery’s nominal voltage. The 12.8V column represents a typical four-cell LiFePO₄ battery; 12V represents a nominal 12V system.
Step-by-Step Calculation Examples
Example 1: Sizing a 12V Dual-Battery System
Suppose you’re adding a 512Wh portable power station to your ute canopy setup. Converting that capacity to amp hours at 12V gives:
512Wh ÷ 12V = 42.7Ah
So 512Wh is roughly 43Ah on a 12V system.
Example 2: Stepping Up to a 24V Caravan Circuit
If your off-grid caravan runs on 24V and its solar panels generate 2,400Wh, here’s what that is in amp hours:
2,400Wh ÷ 24V = 100Ah
The same 2,400Wh would be 200Ah on a 12V system.
Quick Wh to Ah Conversion Chart for Common Batteries
If you need to convert Wh to Ah, use the table below to find the equivalent amp-hour capacity for a given energy rating at 12V, 24V or 48V.
Battery Capacity (Wh) | Equivalent 12V Baseline (Ah) | Equivalent 24V Baseline (Ah) | Equivalent 48V Baseline (Ah) |
|---|---|---|---|
200 Wh | 16.7 Ah | 8.3 Ah | 4.2 Ah |
500 Wh | 41.7 Ah | 20.8 Ah | 10.4 Ah |
1,000 Wh | 83.3 Ah | 41.7 Ah | 20.8 Ah |
1,200 Wh | 100.0 Ah | 50.0 Ah | 25.0 Ah |
2,000 Wh | 166.7 Ah | 83.3 Ah | 41.7 Ah |
2,400 Wh | 200.0 Ah | 100.0 Ah | 50.0 Ah |
3,600 Wh | 300.0 Ah | 150.0 Ah | 75.0 Ah |
Common Conversion Mistakes to Avoid
Confusing instantaneous Watts with Watt Hours: A 60W portable car fridge does not necessarily use 60Wh every clock hour because its compressor cycles on and off. This distinction also matters when deciding what size portable power station you need.
Using full-charge or live terminal voltage instead of nominal voltage: A 12V-class lithium iron phosphate (LiFePO4) battery may sit above its nominal 12.8V when charged. Use the manufacturer’s nominal voltage for capacity conversion; using a higher momentary voltage will understate the equivalent amp hours.
Ignoring the base voltage of small electronics: Power banks are often labelled “20,000mAh” (20Ah). That rating is worked out at the cell’s nominal voltage, typically 3.7V, not the 12V used for this comparison. Same pack at a higher voltage means fewer amp hours, so on 12V it’s a long way short of 20Ah.
Why Does Battery Voltage Change Your Ah Calculation?
Watts are volts times amps, so the same power at a higher voltage takes less current. That’s why the same stored energy works out to fewer amp hours on 24V than on 12V.
How to Identify the Correct Battery Voltage
A battery’s spec lists a nominal voltage plus cut-off thresholds, and that’s the figure to use for the conversion. Automotive and touring setups generally run at one of three voltages:
12V Systems: Standard for passenger vehicles, 4WD starter circuits, basic camper trailers and entry-level dual-battery kits.
24V Systems: Common across heavy commercial rigs, expedition trucks, larger off-grid caravans and high-thrust marine trolling motors.
48V Systems: Used in some larger off-grid and hybrid setups running high-wattage air conditioning, induction cooktops or other substantial loads.
Compare Nominal Voltages Across Battery Chemistries
Battery chemistry sets the nominal voltage of each cell and, in turn, the voltage of the pack built from those cells:
Battery Chemistry | Typical Cell Nominal Voltage | 12V-Class Pack Nominal Voltage |
|---|---|---|
Lead-Acid (AGM / Gel / Wet) | 2.0V per cell (6 cells) | 12.0V |
Lithium Iron Phosphate (LiFePO4) | 3.2V per cell (4 cells in series) | 12.8V |
Lithium Nickel Manganese Cobalt (NMC) | 3.6V–3.7V per cell (3 or 4 cells) | 11.1V to 14.8V |
A 12V-class LiFePO4 pack sits at a nominal 12.8V so a 1,280Wh battery works out to:
1,280Wh ÷ 12.8V = 100Ah
Don’t run the numbers at 12V or you’ll get about 106.7Ah and overstate the capacity.
How Can You Apply Wh to Ah Conversion in Real-World Scenarios?
Out bush, you need to work out how much energy your gear uses and allow for the losses along the way.
Convert Appliance Energy Consumption From Wh to Ah
Most portable appliances list their power draw in watts on the label. Multiply that wattage by the hours it runs each day to get the energy use in watt hours. Divide that by the system voltage to get the daily amp hours.
For example, a 45W 12V compressor fridge running about 40% of the day (9.6 hours) uses:
45W × 9.6h = 432Wh/day
At 12V, that equals:
432Wh ÷ 12V = 36Ah/day
How Do Power Losses Affect Usable Battery Capacity?
Bench-test calculations rarely match field performance because real-world physics intervenes:
Inverter Losses: Inverters typically run at 85% to 92% efficiency when converting 12V DC to 230V AC for gear like blenders or laptops. Running something that needs 100Wh of AC energy will often pull 110Wh to 118Wh from your DC battery bank.
High Ambient Heat: In an Australian summer, temperatures over 40°C in the canopy speed up battery wear and keep fridge compressors cycling for longer, which pushes up your total amp-hour draw.
Depth of Discharge (DoD): Traditional AGM batteries shouldn’t be drawn down past 50% if you want to avoid rapid degradation, which leaves roughly 50Ah usable from a 100Ah lead-acid battery. Quality LiFePO4 cells, on the other hand, can be run down to 100% DoD without immediate cell damage so you get their full rated capacity. Plenty of tourers still cap it at 80% to 90%, purely to stretch the battery’s cycle life.
Calculate Battery Capacity for Australian Camping and Caravan Use
For a remote camping trip, start by estimating how much energy your essential devices use each day. Take a phone, a camp light and a camera for example. A phone might need about 15Wh for a full charge, a 5W camp light running for five hours uses 25Wh, and a camera may use around 20Wh. Together, that’s roughly 60Wh per day:
15Wh + 25Wh + 20Wh = 60Wh/day
For two or three days without reliable solar charging, you’ll need about 120–180Wh:
60Wh × 2 days = 120Wh
60Wh × 3 days = 180Wh
Don’t size right to the bare minimum, though – you want enough headroom to cover inverter losses, voltage drop in the cables and overcast days when the solar can’t keep up. A power pack around the 200Wh mark should cover these small devices for several days with a bit to spare.
At 286Wh, the EcoFlow RIVER 3 Plus Portable Power Station sits well above that 120–180Wh baseline, which gives you enough buffer if cloud rolls in and cuts into your solar input. How long that lasts will depend on the weather and how you use your devices.
Compare Portable Power Stations With Traditional 12V Batteries
Traditional 12V auxiliary batteries are usually rated in amp hours (Ah) while portable power stations are rated in watt hours (Wh). To compare them, multiply amp hours by voltage.
A 100Ah, 12V battery stores about 1,200Wh:
100Ah × 12V = 1,200Wh
Stepping up, the EcoFlow DELTA 3 Max Plus Portable Power Station is rated at 2,048Wh, or about 170.7Ah if you use 12V as the reference voltage:
2,048Wh ÷ 12V ≈ 170.7Ah
A single DELTA 3 Max Plus packs about 1.7 times the stored energy of a typical 100Ah 12V battery. If you need plenty of storage but don’t want the hassle of building a custom 12V dual-battery system from scratch, an all-in-one power station is a straightforward alternative. The DELTA 3 Max Plus supports expandable battery modules so you can scale up your storage capacity down the track without replacing your original hardware.
Conclusion
Converting watt hours to amp hours helps take the guesswork out of sizing an off-grid power system. The basic rule is simple: divide watt hours by the system voltage to get amp hours and multiply amp hours by voltage to find the total stored energy. A standard 100Ah 12V battery is a handy benchmark at around 1,200Wh, but you still need to allow for inverter losses, temperature swings and depth of discharge when choosing your gear. Whether you go with a custom hardwired dual-battery system or a self-contained portable power station, get the setup right and your fridge stays cold, your lights stay on and your gear keeps running in the outback.
FAQs
Is 200W the Same as 200Wh?
No, 200W measures instantaneous power output while 200Wh measures energy used or stored over time. A 200W camping appliance running non-stop for one hour uses exactly 200Wh of energy.
How Long Will a 3000W Inverter Run on a 100Ah Battery?
In theory, a 100Ah 12.8V LiFePO4 battery (1,280Wh) running a 3,000W inverter at around 90% efficiency would go flat in about 20 to 23 minutes. In practice, though, it won’t run that load at all. At 3,000W the current draw is roughly 260A at 12.8V (over 275A at 12V). Most standard 100Ah lithium batteries are rated for 100A (1C) continuous discharge, so the internal Battery Management System (BMS) trips straight away. To run a 3,000W inverter safely you need 24V or 48V, or a parallel bank of at least three 100Ah batteries sharing the load.
Do Batteries With Higher Ah Last Longer?
Yes, as long as you’re comparing batteries at the same voltage. More Ah means more runtime between charges, and with the same load a 200Ah 12V battery will last twice as long as a 100Ah 12V battery.
How Do I Convert kWh to Ah?
To convert kilowatt hours (kWh) to amp hours, first multiply the kWh value by 1,000 to get watt hours, then divide by the nominal voltage you’re running. For example, a 2.4kWh battery holds 2,400Wh, which works out to 200Ah on 12V (2,400Wh ÷ 12V = 200Ah). On a 12.8V LiFePO4 pack the same energy comes to roughly 187.5Ah (2,400Wh ÷ 12.8V ≈ 187.5Ah).