You have to know your bike wheel size to order the Vekkit eBike kit. Look at your bike tire (on the front wheel) and find numbers like on a photo below.
Then open a 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