How can I tell which size chain my bike uses?
After learning how to break a chain and reattach it, and also how to add and remove a master link, I find that I can now do much more in the way of maintenance at home. I'll no longer need to bring my bikes into the shop simply for a new chain... if I can only figure out how to identify what size chain I'll need to order.
Is there a simple way of telling what size and type of chain I'll need to order to replace the chain on a bike? Do I measure the chain links? Count links? Count gears on the cogs?
If it helps, some of my bikes' drivetrains have internal hubs, some have derailer gears.
this question is answered here  with totally different focus.  http://bicycles.stackexchange.com/questions/2704/heavier-thicker-chains-and-gears-for-winter-due-to-salt/2721#2721
@hhh - Definitely related. Good background info there, but the question doesn't get into how to ID a given chain's size. (Thanks for the link, I added the [chain] tag to that question to make it easier to find.)
Bought a used carbon bike and I'm going through the motions of customizing it. I'm new to cycling but have the mechanical aptitude/ "fix it myself" curiosity. Chain broke on my first ride, for the first time ever. All other tri or steel road bikes I use, have never done that. I've repaired a link on a mountain bike once but I was overwhelmed w/ all the different type of chains online. I feel bad asking these questions to my LBS, due to the fact I'm spending my money online. This page answered all of my questions (although I have questions to many other cycling needs). Thank you so much!!!
Actually 10 speed is not "one more" than a 9 speed. What people call 10 speed is a "2 chainrings x 5 sprockets" bike, and what is called 9 speed is a "(N) chainrings x 9 sprockets" bike. Since there are 9 sprockets on the rear, the chain for a 9 speeder is narrower than chain for a 10 speed bike.
If you are using a bike with a derailleur the number of cogs on the rear hub will determine the chain size you will need. They are always 3/32" chains.
You can get a 5/6/7-speed, 8-speed, 9-speed, or 10-speed chains.
If you can't find a chain that matches your cluster pick a chain for a larger number, for example if you have an eight-cog cluster you can use a eight, nine or ten-speed chain, but you shouldn't use a 6 or 7-speed chain.
Internally geared hubs will have their own specification for the size chain they require, and single-speed, fixie, BMX bikes, and probably some older bikes use 1/8" chains.
I have some IGH bikes and some derailer bikes; will add that to my original question to help clarify what I'm looking for.
and 11 speed chains. You can probably also get 5 speed chains but I think they might be the same width as 6 speed (SRAM and Shimano both just sell 5-6-7 speed chain these days). Campagnolo 10 speed chain is not compatible with Shimano 10 speed chain, and there's a third brand of chain/cassette/derailleur/shifter that's not compatible with either despite claiming to be. Summary: 10 speed is a pain.
A few hub gears use 8 speed chain, most use 1/8". It's determined by the cog thickness, as a 1/8" chain will tend to catch on the teeth of a 3/32" cog. Similarly with chainrings.
The info regarding number of gears for a chain here is incorrect. 5,6, and 7 speed chains can use the 7 speed. 7,8,9,10 and 11 speed chains each use a specific chain. None of these are compatible with each other. I might use a 7 or 8 speed interchangeably, in an emergency, but I wouldn't recommend it.