Amp Hour Calculator | Battery Capacity Calculator, Ah↔Wh (12V–48V)

Use our Amp Hour Calculator and Battery Capacity Calculator to convert Ah ↔ Wh, size LiFePO4 and lead-acid battery banks, and estimate runtime for 12V, 24V, 36V, and 48V systems.

Enter your device watts, hours per day, system voltage, inverter efficiency, and depth of discharge (DoD)—the tool instantly returns required capacity in Ah/Wh/kWh and expected runtime.

Perfect for solar, RV, marine, golf cart, and off-grid power planning, it supports series/parallel banks and days of autonomy so you can right-size with confidence.

Use it to compare results to our Epoch LiFePO4 batteries and other packs, or quickly run amp hour to watt hour and watt hour to amp hour conversions (Ah = Wh ÷ V; Wh = W × h). 

Fast, accurate, and free!

Amp-Hour & Battery Capacity Calculator (Epoch Model Preload)

Size your battery bank and estimate runtime. Supports LiFePO4 and lead-acid, with inverter efficiency, depth-of-discharge (DoD), and days of autonomy. Use the Epoch picker to auto-fill voltage & capacity.

Ah = Wh ÷ V Wh = W × h Energy ≈ V × Ah

Quick Start: Preload Your Epoch Battery Specs

Choose a model to preload Voltage & Ah.
How many of this model in your bank.
Check datasheet for series/parallel limits.
Resulting bank: — V × — Ah (≈ — kWh)

1) Load → Required Battery

Enter devices; we total daily energy and apply efficiency, autonomy days, and DoD to size a bank.

Tip: For DC loads set efficiency to 100%. For AC through an inverter, 88–94% is common.
Device Watts Hours/Day Qty Daily Wh
960.0
Nominal DC bus.
Use 100% for DC-only loads.
LiFePO4 commonly 70–90%; lead-acid ~50%.
Total Daily Load: 960 Wh/day (40.0 avg W)
Adjusted for Efficiency: 1066.7 Wh/day
Energy for Autonomy: 1066.7 Wh
Required Bank (usable): 1066.7 Wh
Required Bank (nameplate): 1333.3 Wh → 27.8 Ah @ 48 V

2) Battery → Runtime

Estimate runtime for a known bank and load (includes DoD and efficiency).

Usable Energy: 3840 Wh
Estimated Runtime: 6.9 hours (06:54)

Engineering Notes & Best Practices

  • DoD vs cycle life: LiFePO4 is commonly 70–90% usable per cycle; lead-acid often ~50% for longevity.
  • System voltage: Higher DC bus (24/36/48 V) lowers current for the same power, reducing copper losses.
  • Temperature: Cold reduces capacity and charge acceptance; consider heated packs or low-temp protections.
  • Safety: Fuse strings, add a main disconnect, and follow BMS/charger limits. Size wiring for peak current.