From The Maker 

We simplified sipping with the Rambler® Bottle Straw Cap. Just flip it open, take a sip, and close it tight to stay moving. It’s leak-resistant, easy to carry (thanks to the TripleHaul™ Handle) and accommodates our wide straw, so you get more drink with every sip.The Straw Cap is compatible with all YETI® Rambler® Bottles. Use the measurements below to cut straw according to your bottle size.
12 oz - 4 5/8"
18 oz - 6 5/8"
26 oz - 7 1/4"
36 oz - 7 7/8"