For starters I'm capable of sizing a bike...

But, I'm building a bike as a gift for a family member, and the other family members want me to keep it a surprise...which makes some of the sizing issues difficult. So I'm asking a bit of a poll question I suppose.

The individual in question is 6' even in height. My thought was that a 56cm touring frame would be ideal, but neither of the frames I'm looking at come in that size. My choices are 54cm or 58cm. I know for a fact that the 54cm will have zero standover issues for a 6' person, but it may be to cramped in the top tube, or I may have to raise the saddle too high to make it work. I worry though that 58cm may provide some top clearance issues.

Choices choices. At only 5'6" myself I'm not really capable of getting a good hack on those proportions on my own...I'm going to try to find a 6' rider at the LBS...but some answers from the crowd here may be very helpful. Thanks.

58cm

At 5'8", I take anywhere from a 52 to a 55. My 5'11" brother takes anywere from a 55 to a 58. It depends on the frame. I can't imagine a six footer taking anything as small as 56 unless he likes a really odd fit or the bikes runs big, more likely a 58-59. A leggy six footer might need a 60 with a shorter top tube or quite short stem.

Seems to me it would be very difficult to properly size a bike knowing only the height. Why not give him a picture of the bike as the gift and then get him properly fitted?

I am 6' and used to ride a 58. My legs seem to be shrinking, because most bikes that fit me now are 56.

Does a family member have access to the gift recipient's clothing? You might be able to figure out needed stand over based on pants inseam... stand over at or just below the pants inseam length (unless the recipient wears their pants extremely short or long) should be in the right range.

+1 And since you're building the bike, just wrap up a part or two that isn't size-dependent, and let that be the surprise.

A 58 cm would probably work especially if it has a sloping top tube (compact frame).

Does he look like this? You might need a longer top tube.

At 6', my touring bike is a 61 (85 Trek 620). With the exception of the tandem, all of my bikes are between 61 and 63 cm with "short" top tubes. The tandem is about a 59 with a long top tube and fits poorly.

As you can see from the range of sizes suggested in this thread, this choice is fraught with peril and knowing only a height and a seat tube length is nearly useless for proper sizing.

I suppose you could get measurements under a false pretense and enter them into one of the online fit calculators. That'll help a fair amount but the only definitive answer comes from riding and experience.

Quite so.

Of course, I'm aware of the difficulties and the perils, and have explained them all. However, the family members are insistent on presenting him with the completed product...so I am trying to oblige. They want to have one of those startling big unveiling moments.

I figure if I can just get the standover in the ballpark, we'll go for a ride and figure out some of the little things, possibly swapping stems, adjusting saddle fore/aft position, etc.

My LBS that's helping me with the parts and build is aware of those issues, and will work with me on swapping some of those "fine tuning" parts.

Incidentally, I ordered the 58cm. Thanks for the help.