Ah (Amp-hours)


this web page runs locally on your browser on your machine, no data is transmitted to a server unless you use bookmarks. then it submits to same page (nothing active on server side) and builds a URL. it's just a simple calculator I have made provisions for making the values bookmarkable if you wish to share the information.


Ah (amp*hour) and mAh (1/1000 Ah) is a measure of power a battery can deliver on a charge.

some generators have a battery. the battery output is connected to a voltage inverter which runs your device (well, there's also a charging circuit, but we are ignoring the charging circuit in this calculator since it's not relevant to what we are trying to find which is the running time you can get).

the sample application for such a generator here is for time lapse photography if you have a camera that supports that video feature.

generator calc

to specify Ah, put in a number like 40Ah. to put in mAh, put in 2000:mAh, this takes SI and IEC units.

for Volts, put in 1.2VDC or 12VDC, or for VAC put in 120VAC or 240VAC.

Generator Name:
Battery Ah:
at Battery VDC:
at Efficiency: (heat loss turns any advertised 99% or .99 efficiency to 80-85%)
multiplying these 3 gives you (generator output watt-hours) so dividing that by your
Inverter Output Volts: (accepts VAC, V, Volts, VDC)
gives you Ah at that VAC. if you divide that by your device usage current listed on the power supply of the device you want to run as a load at that inverter output voltage:
Device Usage Amps:
Load Device Name:
you get runtime in hours, more specifically of theoretical estimated usage time, best case.

what you are doing is merging (multiplying) the battery Ah and V and reworking it like silly putty or clay into the interter voltage equivalent. you don't get as much Amps when you do that usually since inverters usually pump up the voltage at the cost of Amps.


firefox is the best browser to view this with, since it implemented MathML in HTML5 like they should.

device_usage_hours = battery_Wh = battery_Ah × battery_VDC × generator_efficiency_percent 100 × inverter_out_V × device_usage_A

battery_Wh inverter_out_V = inverter_out_Ah

inverter_out_Ah device_usage_A = device_usage_hours

battery_Ah × battery_VDC inverter_out_V device_usage_A = device_usage_hours