Size to size, using the same grade of tippet 7X, 6X, 2lb, 4lb, etc. Fluorocarbon tippet, sinks faster than mono. Tippet is fly fisherman talk for leader. Only our "leaders" are a tapered section between fly line and tippet section. Do I have ya confused yet?
To get back to your question about tippet length. Long tippets (leaders) are needed for high water. Generally a lot more than most folks actually ever use. A common mistake. It's hard to cast a fly rod with tippet as long or longer than the rod, and a lot of shot to boot.