Enter both values to calculate amp hours
Watt Hours (Wh)
Volts (V)
Common:
Amp Hours (Ah)
Result will appear here
Understanding Battery Capacity
The relationship between amp hours and watt hours follows the Energy Formula:
- Energy (Wh) = Capacity (Ah) × Voltage (V)
- Capacity (Ah) = Energy (Wh) ÷ Voltage (V)
For Solar Battery Systems
Understanding these relationships helps you:
- Compare batteries - Wh lets you compare batteries of different voltages
- Size your system - Calculate how long your loads can run
- Plan upgrades - Understand capacity when changing voltage
- Match components - Ensure charge controller and inverter compatibility
Real-World Solar Examples
Tesla Powerwall in Amp Hours
The Tesla Powerwall stores 13,500Wh. At 48V (common off-grid standard), that is 281.25Ah. The same energy requires more amp hours at lower voltage.
Sizing a 12V Battery Bank
A camper van using 2,400Wh per day needs 200Ah at 12V. With LFP at 90% usable DoD, you need at least 222.2Ah total — a minimum of three 12V 100Ah batteries.
Converting a 48V System Requirement
An off-grid cabin needing 9,600Wh of storage at 48V requires 200Ah. At 12V, the same energy would require 800Ah, making wiring impractically heavy due to high current.
When You'll Need This Conversion
- Selecting Batteries from Energy Needs — Critical loads consume 5,000Wh overnight. At 48V: 104.2Ah minimum. Accounting for 90% DoD: 115.7Ah needed. A single 48V 200Ah battery provides ample capacity with cloudy-day reserves.
- Matching Battery to Charge Controller — Charge controllers are rated in amps, not watts. Pushing 3,600Wh into a 24V bank over 5 sun hours: 150Ah total, 30A average charge current. A 40A controller is appropriate.
- Utility Bill in Battery Terms — A homeowner using 30 kWh/day needs 625Ah at 48V to store one full day. This shows why whole-home battery backup requires six or seven 48V 100Ah batteries.
Solar Tips & Common Mistakes
Wire Gauge Depends on Amps, Not Watt-Hours: A 12V 100Ah system delivering 1,200Wh requires 100A-capable wiring, while a 48V 25Ah system delivering the same 1,200Wh needs only 25A wiring. Higher voltage saves significantly on copper costs.
Do Not Mix Ah Ratings in Parallel: When paralleling batteries, all must be the same voltage, chemistry, and ideally same Ah rating and age. Mismatched Ah causes uneven cycling, reducing lifespan.
Lead-Acid vs LFP Usable Ah: A 12V 200Ah lead-acid is only usable to 50% DoD: 100Ah (1,200Wh). A 12V 200Ah LFP at 90% DoD gives 180Ah (2,160Wh). Always convert to usable Wh first.
Solar Calculators
Related Conversion Calculators
Last updated: January 5, 2026
