You have to know your bike's wheel size to order the Vekkit eBike kit. Look at your bike tire (on the front wheel) and find numbers like on the photo below.
Then open the kit configurator and choose your wheel size. We added 2 sizing systems to our kit configurator - ISO (for example, 37-622) and french (for example, 700 x 35c) so you can use any.
Check out this article for more details