BMX Tube Size Guide
Buying BMX tubes is easy, but the sizing can look confusing. The industry standard for BMX tubes is to measure the width while not inflated/flat. Therefore, once filled with air, the tube stretches and measures way more than what the label/packing indicates. This means, even though the packing says for instance: 20" x 1.9"-2.1", the tube will still be compatible with 1.70"- 2.5" tires when inflated/pumped.
As a customer, you should therefore not worry too much about the dimensions of the tube, as they do fit bigger/smaller tires than recommended.