This page looks at the problem of sizing the correct battery pack for your electric bike, based on two inputs:
- Type of Riding anticipated – minimal assist, typical assist, or power-hungry.
- Typical Trip Distance
This calculator can be used to estimate the battery pack size for a DIY electric bike kit, based on the type of riding and the typical distance traveled. Secondly, most purpose-built ebikes have the battery pack (and standard capacity) built into the bike, but if you have an option of battery pack sizes, this calculator can give you an idea of what a larger battery pack may provide you in terms of range.
Input can be shown in kms or miles using the toggle at the top of the calculator.
Type of Riding – Watt-hour demand
When determining the type of riding, and related watt-hour demand (Wh / mile or km) of the motor on the battery, a lot of factors can contribute to this number. The following are just a few of these factors:
|Improves Range||Decreased Range|
|Lighter Bike / Rider / Cargo||Heavier Bike / Rider / Cargo|
|Flat Terrain||Hilly Terrain|
|Narrow Road Tires||Wide Knobby Tires|
|Continuous Riding||Frequent Stop & Start|
|Paved Surface||Soft Trails|
|More upright Riding||Lower stance road ebike|
|Low Average Speed||High Average Speed|
In order to make this calculator fairly simple to use, I’ve noted three types of riding (minimal assist, typical assist, and power assist) to show the general range of power demand in these types of riding. The value is on a slider, however, so you can pick a specific watt-hour demand that suits your situation.
Try it out below, Inputs via the two sliders and output at the bottom in yellow. Several battery sizes (Amp-hours) are provided, depending on the voltage of your battery. I’ve added some more detail below about the math behind the calculator if you’re interested.
The Math Behind the Calculator is fairly simple, using the following units and terms:
Battery Capacity Required (Wh) = Power Demand per distance traveled (Wh / mile or km) x Typical Distance Traveled (miles or km)
Watt-Hour (Wh) is a unit of energy used to describe the amount of power (watts) used in one hour. This number is an indication of the size of your battery and the subsequent range of your ebike.
Watt-Hour (Wh) = Amp-hours (Ah) x Volts (v)
Amp Hours (Ah) is the amount of current a battery can discharge over one hour.
Volts (V) the difference of potential that would drive one ampere of current against one ohm resistance. Typical Voltage in Electric Bike batteries is 36v, 48v, 52v, and 72v. These are typically multiples of 12 volts.
Some Other Calculator Options
Bosch has a pretty extensive range calculator where you are able to change all sorts of variables, from rider weight, terrain, type of bike, tires, etc. Understandably, this calculator is limited to the Bosch line of products but has some helpful information.
Grin Technologies has a very detailed simulator with the ability to add custom batteries and controllers and set a wide variety of vehicle parameters to see how factors such as throttle level, bike weight, hill grade affect the performance of an ebike.