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I am just shopping for used bikes right now online. I want to try and save myself a trip to visit the bikes by determining which bikes will fit me.

Does anyone have an approximate height-bike size conversion chart or inseam-bike size conversion chart?

I know that this will not 100% accurate as Sheldon Brown observes. I was just hoping to get an approximation.

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7 Answers

IMO single most important factor of cycling joy is FIT!

This is a great tool and worth the effort: http://www.competitivecyclist.com/za/CCY?PAGE=FIT_CALCULATOR_INTRO

I have used it myself and referred countless folks to it, all with great success! Good luck!

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Would you buy second hand shoes online, not knowing what shoe size you were, particularly if there is the risk that they might have been stolen?

Probably not, when put like that!

With footwear you know your size. This is something established last time you bought some shoes, probably in a shoe shop where sales staff assisted you. They might have made you pace about and checked where your big toes were - that kind of stuff. They might have also tried you on the larger - or smaller - sizes to get it right. Although shoe shop sales staff are not rocket scientists, some of them are very good at what they do - find people the right shoes, ones that fit. They might take a dim view of those that insisted on only buying second hand shoes off the internet, without even bothering to know their shoe size.
Sure there is probably some chart out there on the internet that you can enter your inseam length into and get some shoe size out, but in taking that approach you may never know what a properly fitting is.

Bicycles are remarkably similar to shoes in that they have to fit YOU. Yes, you can adjust the seat and bars (much like you can adjust the laces on a shoe) but you still need to get the size right in the first place. If you already have a bike, e.g. a 19" frame MTB then you can get another one online of a similar size. But you are not there yet.

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I found the Rivendell frame sizing article to be quite illuminating during the process of test-riding dozens of bikes to try to discover the proper size:

http://www.rivbike.com/kb_results.asp?ID=41

Ultimately a bike that feels just a tiny bit too big in the store / out of the box is probably the right size after dialing in e.g. seatpost height, seat angle, handlebar height/angle, crank length, etc.

If fiddling with the setup extensively is not in the cards, I think you can get an OK sizing by going one or two smaller -- whatever feels immediately 'controllable' off the rack.

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Thanks @AmericanLuke, fixed the link. –  Mike Simpson Jul 13 '13 at 5:00
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Kind of depends what you're looking for. For classic, straight top-tube roadsters, a good starting point is "standover height". You should be able to straddle the top tube with your feet flat on the ground.
Unfortunately, this is not how bikes are normally measured; "frame height" is measured from the center of the bottom bracket to the top of the seat tube. Go to a bike shop and look around. Straddle a few bikes and have the friendly shop folks help you get an approximate size. Then go looking for used....
Warning... If you are not an experienced cyclist who knows what to look for then buying used can be fraught with problems.... Also, bear in mind that that straight-top-tube roadster is increasingly a rarity; many manufacturers use a variety of sloping top tubes now which defy measuring in the old-fashioned way.

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You should be able to look up the frame geometry (useful for comparing to an online fit tool) on the manufacturer's web site if the bike is new enough.

Many times there will also be an approximate frame size-height sizing chart available online as well.

I've tried the online fit calculator that GuyZee recommends and it seems to work well for me, for what that's worth.

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The most comprehensive bike sizing chart I've found is from Wiggle and it also explains how to use the charts.

If you'd rather avoid shop-bias then this article also has some explanation and a simple chart at the end.

Beyond that you should probably go for a professional bike sizing from someone like BikeDynamics (if you're in the UK). This is pretty cheap compared to the price of a bike.

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Also have a look at CANYON's calculator: http://www.canyon.com/_en/tools/pps.html

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