The listed price is for a single zip. 

Light-Weight Invisible Zipper 

This is a lovely quality light weight invisible zip (with enclosed end).  It's perfect for lighter linens and cottons, viscoses and silks.    

 Zip Length

55 cm

What if the zip is not the length you require?

You can shorten invisible zips from the top or the bottom, and there are many excellent online tutorials to show you how you can make this easy modification.