How Do I Size My Bike Chain?

Bike chains can be surprisingly complicated. While these critical parts might look like they’re all the same, bike chains come in many widths and need to be cut to the correct size for your bike. 

Use the length of the old chain. You can also size your chain by placing it on the largest cog on the front chainring and on the largest sprocket on the cassette. Adding one link where two ends meet is the right size. The width of the chain is determined by the number of sprockets on the cassette.

Here’s a quick guide that will cover everything you need to know to begin the process of sizing your bike chain and getting the right parts for your bicycle.

How Do I Size My Bike Chain?

Bike chains vary in both length and width.

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The width of your bike chain is determined by your cassette and derailleur (the parts of your bike that shift gears on your rear wheel). 

If you’re on a single-speed bike or a bike with a hub gear system, you’ll usually use a chain that’s slightly wider than the chains used on geared bikes. 

In general, if you’re riding a bike with 6, 7, or 8 gears in the back, you can buy a standard chain designed for any other bike with 6, 7, or 8 speeds. 

If you’re riding a bike with 9 speeds or more, however, you’ll want to look up your cassette and derailleur and buy a chain designed specifically for your groupset.

The length of your chain is determined by how big your biggest gear is and how far apart your cassette and chainring are (essentially your chainstay length). 

Bike chain manufacturers sell chains that are longer than most cyclists need, allowing customers to trim the chains to the appropriate length themselves. Unless you’re running a complex suspension setup, you’ll be able to cut any new chain down to size and use it on your bike.

How Do I Know the Right Bike Chain Length for My Bike?

If you can, the easiest way to figure out the correct chain length for your bike is to measure your old chain. 

Old chains have a bit of stretch, so try to check your measurements by counting links and doing a bit of math. Each link should measure 0.5.” 

Once you’ve acquired a new chain, simply lay it down side-by-side with the old one, match up each rivet, and mark the spot where your old chain ends. Don’t forget to account for a master link here — if you’re not recycling your old master link, you’ll need to pop the new link onto the new chain before you compare.

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If you don’t have your old chain, your old chain wasn’t sized correctly, or you’d like to double-check your work, try sticking your new chain on your bike and using your bike itself to determine its length. 

How do you size a chain?

If you have gears, move the rear derailleur out of the way so it sits over the smallest cog. Set the front derailleur to sit over the largest cog. Drape your chain over the front of the largest cog on your front chainring, then feed the other end over the largest cog in the back, but do not feed it through your derailleur. 

Crank the front chainring until the chain comes around to the 5-o-clock position, then pull the other end of your chain forward until they meet. With half of your master link on, find the first spot where you could connect an inner plate to an outer plate. Next, add two rivets worth of slack (or one whole link), then mark a rivet. You’ll want to drive out this rivet and then connect up your chain.

While the chain sizing process above works for most bikes, some bikes might challenge it. Bikes with rear suspension can be pretty complicated. The distance between the cassette and the chainring on these bikes changes as your suspension does its job

You’ll need to factor this in by removing your suspension and lifting your rear wheel all the way up before you go through the sizing process. Additionally, if you have a Campagnolo derailleur, you’ll want to follow a different, more complex procedure most of the time. 

Finally, if you’ve got a high-pivot suspension bike, you’ll need to fully account for both your bike’s suspension and the fact that it needs a lot more chain than other bikes. This means that you’ll often wind up buying two chains and linking them together.

How Do I Know the Right Chain Width for my Bike?

Most single-speed bikes use chains that have an internal width of 1/8″. In most cases, these chains are interchangeable, but some manufacturers do make single-speed bikes that have narrower cogs so they can share parts with geared bikes. 

If you think you’ve got one of those bikes, try to look up any information you know about the make and model or the components used in the drivetrain. Alternately, take a tape measure and measure the internal width of your chain. If it’s noticeably smaller than 1/8′”, you’ll probably need a 3/32″ chain.

Geared bikes with 6, 7, or 8 speeds in the back usually use chains that have an internal width of 3/32″. With very few exceptions, these chains are freely interchangeable. This means that you shouldn’t have to worry about brand or design. 

It’s still a good idea to do a bit of research about your specific bike and the components you’re using to shift gears, but you’ll probably find out that you just need a standard 3/32″ chain.

If you’ve got a geared bike with 9 or more speeds, you’ll need to do a bit of digging to figure out which chain to use. Bikes with 9 or more gears use chains with an internal width of 11/128.” This is very slightly smaller than the 3/32″ for 6, 7, and 8 speeds. it might not sound like a lot, but there’s definitely enough of a difference to cause problems.

9, 10, 11, and 12-speed systems pose a unique engineering challenge. In order to fit all of the necessary cogs onto the cassette, bike manufacturers need to make the space between each cog a little bit smaller. 

The gap has to get narrower and narrower as you add gears. 12-speed SRAM systems use chains that are 13/64″ wide, compared to the 6/64″ wide chains used on 6, 7, and 8-speed bikes.

Unfortunately, there’s a huge amount of variance in terms of outer chain width once you get above 9 speeds. It’s a good idea to buy a chain designed specifically for your derailleur and cassette. 

This means matching the brand of your other components and following the manufacturer’s advice to the letter. It is very important to match the brand of your chain to the brand of your cassette. Your bike might have the same number of speeds as another bike, but that doesn’t mean that his cassette follows the same spacing pattern that yours does. 

Additionally, as you get more and more speeds, the smallest chainring gets smaller and smaller. Chains for these bikes are often directional and have special shapes to allow them to bend around a small cog easily. 

Using the wrong chain on these tiny cogs can cause you a whole slew of problems, from breaking your chain early to damaging your cassette and derailleur.

What Happens if my Chain is Too Wide or Too Narrow?

The first and most basic symptom of a poorly sized chain is that your bike will shift poorly. Over time, you’ll also run the risk of major damage to expensive drivetrain components.

A chain that is too small will wear down your gears much more quickly than a chain that’s the correct size. Wear down your cogs enough and you’ll get issues with your chain slipping and losing grip.

When this happens, you put a lot of stress on your chain, meaning you could very easily break a chain that’s not wide enough. You’ll also probably have issues with the way the chain fits in your derailleur.

If your chain is too wide, other cogs in your cassette will rub against the side. This isn’t good for your chain or your cogs. It’s also quite noisy. Over time, you’ll get some very unusual wear patterns in both your chain and your cogs. You’ll also have trouble shifting and will probably notice some issues with your derailleur.

There are a number of common problems you’ll encounter whether your chain is too wide or too narrow. Your bike will be noisier, it’ll shift poorly, and you’ll probably notice that the chain is winding up in places it shouldn’t be. If you ride your bike for too long, you’ll cause long-term damage to your cassette, run the risk of breaking your derailleur, and eventually break your chain.

Sam Benkoczy

Hi, I'm Sam. I own and maintain 6 e-bikes, 15 regular bikes (road bikes, folding bikes, hybrid bikes, city bikes among others). I learned about bikes from my local bike mechanic as well as from bike maintenance courses. I love being out there in the saddle, and using my bike as a practical means of transportation. You can also find me on my YouTube channel at Say hi to me at

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