A good measure is to top of waders with boots on. This ensures a comfortable length, while allowing some reach while wading.
Rule of thumb for height/length: 5’5” - 5’7” = 51”, 5'8" - 5'10" = 52", 5'11" - 6' 2" = 53", 6'3" - 6'5"= 54-55".
I just used mine today and it’s really nice, a very solid and dependable staff. This may be the novice in me talking but I love how it “automatically” forms! It’s like the pieces are magnetized to each other. I kept “practicing” in the garage with it when I first received it. And it did a great job on the river today, not merely in the water but on the trail as well. I don’t have any comparison to make to any other staff because I haven’t tried any other, but this one is a tank and seems likely to last as long as I do!
I own one of these, it's "all that". I'm undeniably a fan of durable at the expense of weight and this meets my needs. I have Simms/Folstaff/Orvis/BD/etc options, -have tried pretty much everything available.
I went longer than recommended and am happy that I did, if I'm falling, I want hang onto something 'up there', not something 'over there'. I did have a local gunsmith mill a sharp stainless tip for it as our local tailwater fisheries are extremely slippery.