Ah to Wh calculator
Convert either way, or estimate run time from capacity, voltage and load. Run time uses 80 percent depth of discharge, which suits lead-acid and is conservative for lithium.
- Energy
- 1,200 Wh
The formulas
Wh = Ah x V, and Ah = Wh / V.
Run time in hours = (Ah x V x depth of discharge) / load watts. Depth of discharge is 0.5 for a lead-acid battery you want to last, 0.8 for one you are willing to cycle harder, and 0.9 or better for lithium iron phosphate.
Capacity is rated at a particular discharge rate, usually 20 hours for lead-acid, and falls if you pull current faster. A 100 Ah lead-acid battery discharged over 5 hours delivers closer to 80 Ah. Lithium is far less affected.
Cordless tool battery energy
Tool batteries are sold on amp hours, which makes a 12 V pack look the same as an 18 V one. Compare on watt hours to see what you are actually getting.
| Voltage | 2 Ah | 4 Ah | 5 Ah | 6 Ah | 9 Ah |
|---|---|---|---|---|---|
| 12 V | 24 Wh | 48 Wh | 60 Wh | 72 Wh | 108 Wh |
| 18 V / 20 V max | 36 Wh | 72 Wh | 90 Wh | 108 Wh | 162 Wh |
| 36 V / 40 V max | 72 Wh | 144 Wh | 180 Wh | 216 Wh | 324 Wh |
| 54 V / 60 V max | 108 Wh | 216 Wh | 270 Wh | 324 Wh | 486 Wh |
