Amp-hours are derived—not guessed—from watt-hours and voltage. This guide shows how to calculate amp-hours from watt-hours using the nominal volts your bank will run at.
Benefits
- Formula: Ah = Wh ÷ nominal voltage.
- Convert kWh budgets to Wh, then to Ah at your system voltage.
- Reverse check: Wh = Ah × V to verify pack listings.
How it works
- Start with watt-hours—daily load total, solar storage target, or pack energy rating.
- Divide by nominal bus voltage (12 V, 24 V, 48 V, etc.).
- Read required amp-hours for bank sizing and product shortlists.
FAQ
How do I calculate amp-hours from watt-hours?
Ah = Wh ÷ V. Example: 3,840 Wh target at 12 V → 3,840 ÷ 12 = 320 Ah bank. At 48 V the same energy needs 3,840 ÷ 48 = 80 Ah—always state voltage with the result.
How do I convert kWh to Ah?
First kWh × 1,000 = Wh, then Ah = Wh ÷ V. Example: 5 kWh = 5,000 Wh at 48 V → 5,000 ÷ 48 ≈ 104 Ah. Skipping the Wh step is a common spreadsheet error.
Should I add margin after calculating Ah?
Yes—this gives rated equivalence only. Apply depth-of-discharge (e.g., need 320 Ah rated for 256 Ah usable at 80% DoD) and inverter/charging efficiency before final purchase. Calculate base Ah from Wh first, then inflate for real-world losses.
Technical specifications
- Ah = Wh ÷ nominal_V.
- Wh from kWh: Wh = kWh × 1,000.
- Required rated Ah ≈ (usable Wh ÷ DoD) ÷ V.
- Related: wh-to-ah-converter, ah-to-wh, battery-bank-size.
One division ties energy to capacity
Watt-hours answer how much work the bank must store; amp-hours answer what label to search at your voltage. The calculation is a single division—no iterative solver. 2,400 Wh ÷ 12 V is 200 Ah every time. Document voltage beside every Ah result so a 200 Ah 48 V quote is not mistaken for 200 Ah at 12 V.
From appliance Wh stacks to bank Ah
Sum daily load in Wh from appliance calculators or interval data. Divide by system voltage for minimum rated Ah before DoD. A 1,800 Wh/day RV budget at 12 V implies 150 Ah nominal—then apply 80% LiFePO4 DoD and you shop for ~188 Ah rated, or parallel two 100 Ah packs with headroom.
kWh specs are Wh with three zeros
Residential storage and EV packs market kilowatt-hours. Multiply by 1,000 before dividing by bus voltage. A 10 kWh home battery target at 48 V nominal is 10,000 ÷ 48 ≈ 208 Ah equivalent—useful when comparing a 10 kWh rack quote to 400 Ah 12 V listings that are not the same energy at all.