Ah ↔ kWh Battery Calculator
Convert amp-hours (Ah) to kilowatt-hours (kWh), or size required Ah from a target kWh using battery voltage, efficiency, and depth of discharge.
In Ah to kWh mode, the first value is your battery capacity in amp-hours.
If you work with batteries for solar systems, RV power, marine electronics, backup power, or off-grid setups, you will constantly switch between Ah and kWh. This guide explains the conversion clearly and helps you avoid common sizing mistakes.
What is Ah vs kWh?
Amp-hour (Ah)
Amp-hours measure electric charge capacity. Think of Ah as how much current a battery can deliver over time. A 100Ah battery can theoretically provide 100 amps for 1 hour, 10 amps for 10 hours, and so on (under ideal conditions).
Kilowatt-hour (kWh)
Kilowatt-hours measure energy. Utility bills are in kWh because kWh reflects usable energy regardless of battery voltage.
Why voltage matters
Ah alone is not enough to compare batteries. A 100Ah battery at 12V stores far less energy than a 100Ah battery at 48V. Voltage is the bridge between Ah and real energy.
Core formulas
Wh = Ah × V
kWh = (Ah × V) ÷ 1000
Ah = (kWh × 1000) ÷ V
For practical design, you should also include efficiency losses and allowable depth of discharge (DoD):
Usable kWh = Nominal kWh × (Efficiency/100) × (DoD/100)
Required Ah = (Target usable kWh × 1000) ÷ [V × (Efficiency/100) × (DoD/100)]
Quick examples
Example 1: Convert Ah to kWh
Battery: 200Ah at 12V
- Nominal Wh = 200 × 12 = 2400Wh
- Nominal kWh = 2400 ÷ 1000 = 2.4kWh
If efficiency is 90% and DoD is 80%, usable energy is 2.4 × 0.9 × 0.8 = 1.728kWh.
Example 2: Convert kWh to Ah
Need 5kWh usable at 48V with 92% system efficiency and 90% DoD:
- Required Ah = (5 × 1000) ÷ (48 × 0.92 × 0.90)
- Required Ah ≈ 125.8Ah
You would typically round up for reserve margin, aging, temperature effects, and surge loads.
Common battery voltage reference table
| Battery Bank Voltage | 100Ah Nominal Energy | 200Ah Nominal Energy | 300Ah Nominal Energy |
|---|---|---|---|
| 12V | 1.2kWh | 2.4kWh | 3.6kWh |
| 24V | 2.4kWh | 4.8kWh | 7.2kWh |
| 48V | 4.8kWh | 9.6kWh | 14.4kWh |
How to use this calculator correctly
1) Pick the right conversion mode
Use Ah to kWh if you already know battery amp-hours. Use kWh to Ah if you know energy demand and need to size battery capacity.
2) Use realistic efficiency
Real systems lose energy through inverter conversion, wiring, and battery internal resistance. Typical overall values are often between 85% and 95% depending on hardware quality and load profile.
3) Set depth of discharge based on chemistry
- LiFePO4: commonly 80–95% usable
- Lead-acid: often designed around 50% usable for long life
- AGM/Gel: usually less than lithium for cycle longevity
4) Always include safety margin
After calculating, many designers add 10–30% reserve to handle cold weather, battery aging, and load uncertainty.
Typical use cases
- Solar battery sizing: match daily kWh consumption to storage in Ah at chosen system voltage.
- RV and van life: estimate runtime for fridges, fans, laptops, and lighting.
- Marine systems: translate house bank Ah into real usable kWh at sea.
- Home backup: check how long essential loads can run during outages.
Frequently asked questions
Is Ah the same as kWh?
No. Ah is charge capacity; kWh is energy. You need voltage to convert between them.
Why does my runtime differ from calculator estimates?
Real runtime depends on battery age, temperature, discharge rate, inverter idle draw, and actual load fluctuations.
Should I design to 100% DoD?
Usually no. Deep cycles to 100% DoD can reduce battery lifespan. Follow your battery manufacturer’s recommended operating window.
Can I compare two battery banks using only Ah?
Only if voltage is identical. Otherwise compare in Wh or kWh.
Bottom line
Ah to kWh conversion is simple but critical: energy = capacity × voltage. Add realistic efficiency and depth-of-discharge assumptions, then size with margin. Use the calculator above to quickly move between battery specs and practical energy planning.