Battery planning
Battery Capacity Calculator
Convert Ah, mAh, Wh and kWh using battery voltage, then estimate usable energy from the SOC window and battery health. Start with a prefilled example and adjust the values you know.
Convert battery capacity
Battery capacity calculator
This calculator answers how much energy a battery stores from its charge capacity and voltage, or how many amp-hours correspond to known watt-hours. It also separates nominal capacity from the usable energy available within your chosen SOC window.
Ah to Wh calculation
To convert amp-hours to watt-hours, multiply capacity in Ah by voltage: Wh = Ah × V. For example, 100 Ah at 12 V is 1,200 Wh, or 1.20 kWh.
Wh to Ah calculation
To convert watt-hours to amp-hours, divide energy by voltage: Ah = Wh ÷ V. The same 1,200 Wh is 100 Ah at 12 V, 50 Ah at 24 V and 25 Ah at 48 V. These are equivalent charge values, not three battery recommendations.
mAh to Ah and battery kWh
There are 1,000 milliamp-hours in one amp-hour, so 100,000 mAh equals 100 Ah. Divide watt-hours by 1,000 to express the same nominal energy in kWh.
Nominal versus usable battery capacity
Nominal energy is the battery capacity before planning assumptions. Usable energy uses one SOC-window model: usable energy = nominal energy × usable SOC window × battery health. Starting charge and minimum charge define the SOC window; battery health separately represents remaining capacity relative to nominal/new capacity.
Battery capacity examples
A 100 Ah, 12 V battery has 1,200 Wh nominal capacity. With a 100% starting charge, 20% minimum charge and 100% health, the usable estimate is 960 Wh. Ah cannot be converted to energy without voltage, and capacity conversion is separate from sizing a battery for a load and runtime.
Battery Capacity & Voltage Conversion Cheat Sheet
Quick reference matrix converting Amp-Hours (Ah) to stored energy in Watt-Hours (Wh) and Kilowatt-Hours (kWh) across standard DC system voltages:
| Charge Capacity (Ah) | 12V System (12.8V LiFePO4) | 24V System (25.6V LiFePO4) | 48V System (51.2V LiFePO4) | Typical Use Case |
|---|---|---|---|---|
| 20 Ah | 240 Wh (0.24 kWh) | 480 Wh (0.48 kWh) | 960 Wh (0.96 kWh) | Kayak fish finders, small UPS backup |
| 50 Ah | 600 Wh (0.60 kWh) | 1,200 Wh (1.20 kWh) | 2,400 Wh (2.40 kWh) | Trolling motors, camping power stations |
| 100 Ah | 1,200 Wh (1.20 kWh) | 2,400 Wh (2.40 kWh) | 4,800 Wh (4.80 kWh) | RV house batteries, solar vans, DIY solar |
| 200 Ah | 2,400 Wh (2.40 kWh) | 4,800 Wh (4.80 kWh) | 9,600 Wh (9.60 kWh) | Off-grid cabins, marine vessels |
| 300 Ah | 3,600 Wh (3.60 kWh) | 7,200 Wh (7.20 kWh) | 14,400 Wh (14.4 kWh) | Whole-home battery backup banks |
Battery Capacity & Energy Conversion Formulas
Converts between electrical charge (Ah) and stored energy (Wh/kWh) using nominal terminal voltage, then derives net usable stored energy.
Watt_Hours (Wh) = Amp_Hours (Ah) × Voltage (V) | Usable_Wh = Nominal_Wh × (Start_SOC - Reserve_SOC) × HealthVariable Definitions
Amp_Hours (Ah)Battery Charge Capacity(Ah)- Rated charge capacity at standard C/20 discharge rate.
Voltage (V)Nominal System Voltage(V)- Rated terminal voltage (12V, 24V, 48V, etc.).
Nominal_WhGross Rated Energy(Wh)- Nominal energy = Ah × Volts (or kWh × 1,000).
Usable_SOCOperating Window(fraction)- Starting state of charge minus minimum reserve cutoff.
HealthState of Health (SOH)(fraction)- Remaining capacity relative to factory original.
Engineering Notes & Standards
- 1,000 milliamp-hours (mAh) = 1 Amp-Hour (Ah).
- 1 Kilowatt-Hour (kWh) = 1,000 Watt-Hours (Wh).
Frequently Asked Questions (FAQ)
How do you convert Amp-Hours (Ah) to Watt-Hours (Wh) or kWh?
How many watt-hours is a 12V 100Ah battery?
Can I convert Ah to kWh without knowing the battery voltage?
Why is usable battery capacity lower than nominal capacity?
Related battery calculators
Use the Battery Runtime Calculator to estimate how long a known capacity may run a load, or use the Battery Size Calculator to calculate the capacity required for a load and desired runtime.