Complete Guide To Bike Chain Length: How To Size A Bike Chain

Having the right chain length on your bike is vital.

If your chain is too long, you stand more chance of it dropping off the chainring while you ride. This is especially the case for mountain bikers riding rough terrain.

On the other end of the spectrum, if your chain is too short it could damage your bike’s drivetrain, as it can put unnecessary stress on your derailleur. Or you may find that your chain simply does not fit over the chainrings at all.

With all this in mind, you need to buy the right chain for your bike, but you also have to make sure your chain length is correct.

In this article, we’ll be covering:

  • Bike Chain Length
  • Replacing A Bike Chain
  • How To Size A Bike Chain
  • Exceptions And Considerations For Determining Chain Length

Let’s get into the details of bike chain length!

Bike Chain Length Guide: Title Image

Bike Chain Length

When you buy a new bike chain, it will probably be made up of 116 links.

Manufacturers choose this size as it’s long enough to fit around the largest chainrings while being able to fit around the largest gear on the rear cassette. However, a few other sizes are available to accommodate bikes requiring unusual chain lengths.

For example, some bikes, such as ones used for bike touring, have extra long chainstays. In some cases, the standard 116 links on the chain won’t be enough.

Therefore, it’s best to check the chain length before buying.

A bike mechanic uses a chain gauge to check a bike chain.

Replacing A Bike Chain

Riding with a worn bike chain can damage the gears and chainrings. It will also negatively affect your gear shifting. You can determine if your chain is worn by using a chain gauge. This tool is easy to use, as you just place it onto the chain. If it aligns perfectly with the links, this is your cue to change your bike chain as soon as possible.

It can be tricky to determine how many miles a bike chain is good for, as many factors contribute to chain wear. However, you can expect a chain to wear faster if you ride off-road or in the winter when the road is covered in salt.

But if you look after your chain, you can probably ride 1,500 to 2,000 miles before you need to change it.

When you replace your chain, there’s a good chance you’ll need to shorten the chain length to the optimum size for your bike. However, you may need to extend the chain length on rare occasions.

It is pretty easy to replace a bike chain; you just need the right tool for the job. A chain tool allows you to remove the pins from the chain links and press them back in when you’re done.

Your chain tool will allow you to shorten your bike chain or add links to extend it. You will find that using a bike stand will make replacing a bike chain much easier, as will removing the rear wheel. 

Check out our complete guide to removing and replacing a bike chain here!

A man in a black baseball cap adjusts his bike's chain.

How To Size A Bike Chain

There are a few ways to ensure that your chain length is perfect for your bike. Here are the four most accurate methods on how to size a bike chain.

 #1. Compare The New Chain With The Old Chain

If you are replacing an old chain with a new one, as long as the old one is correct, you can compare its length with the new one.

Lay both chains out next to each other with the outer plates in line with each other. If you choose this method, you should fit the new chain with the master link for an exact comparison of both chains.

In addition to this, it is best to align the chains using the rivets as a guide. This is because the chain length can increase as it “stretches” over time.

#2. The Big-Big Method

If this is the first time you’ve needed to change your bike’s chain, you may have thrown the old one away without realizing how useful it is. So if you don’t have the old chain to compare its length with the new one, how can you determine the correct chain length?

The method for determining bike chain length depends on how your bike is geared. If your bike has a rear sprocket with 36 teeth or less, you can use the “big-big” method to get the correct chain length.

To use the big-big method, the first thing you need to do is shift your front derailleur to the biggest chainring. Then shift the rear derailleur over the smallest gear on the cassette.

Next, wrap your new chain around the largest gear on the back. If your new bike chain has an outer plate at one end, make sure that end goes toward the front chainring, passing it through the derailleur cage. Then hold the chain roughly around the 5 o’clock position on the largest chainring.

Some bike chains use a master link; if this is what you have, fit half of the link. Doing this will be more accurate, as the master link adds an extra half-inch to the chain length.

Pull the lower part of the chain tight on the chainring’s teeth. In addition to this, make sure the chain is wrapped around the largest gear on the rear cassette for accurate chain sizing. Don’t pass the chain through the rear derailleur just yet; you’ll need to add some length to the chain later to account for this.

Locate the closest rivet to where the ends of the chain can be joined. This rivet is your reference point, from which you will add two additional rivets to establish the chain’s cutting point.

However, sometimes when you pull the lower part of the chain tight, an outer plate meets another outer plate, preventing you from joining the two ends of the chain. If this is the case, add one rivet to establish the reference point from which you add the two additional rivets.

Break the chain with a chain tool at the correct size, then join the two ends.

#3. Big-Big Method For 1X Drivetrains.

If your bike has a single chainring at the front and a wide range of gears on the rear cassette, you have a 1X drivetrain. These drivetrains require longer chains, as the largest gear on the cassette often has 42 teeth or more.

Without passing the chain through the rear derailleur, wrap it over the front chainring and the largest rear gear. Offer up both ends of the chain to work out the shortest length where a chain would connect via inner and outer plates.

From this reference point, count 4 rivets to establish the reference point to shorten the chain.

#4. How To Size A Bike Chain With An Equation

A bike chain may look pretty straightforward, but they are somewhat technical components. The way they use inner and outer plates allows them to be connected in increments of 1 inch. This means you can determine the chain length using industrial drive train equations.

First, you need to count the teeth on the largest front chainring and the largest gear on the rear cassette.

Next, measure the space between the center of the crank bolt and the rear axle to the nearest 1/8″. Then convert your measurement into decimal form.

Now use this equation to determine the chain length:

L = 2 (C) + (F/4 + R/4 + 1)

  • L = Chain length in inches 
  • C = Chain stay length in inches 
  • F= Number of teeth on biggest front chainring
  • R= Number of teeth on biggest back cog.
Using a chain tool to reconnect a broken bike chain.

Exceptions And Considerations For Determining Chain Length

If you ride a mountain bike with rear suspension, there is another consideration you need to make when it comes to chain length. As you ride over bumpy terrain, the distance between the cassette and the front chainrings constantly changes. This is because the chain tightens and slackens as the suspension compresses and extends.

To compensate for the movement, you need to disconnect the shock and compress the linkage. Also, if your bike has a chain guide, ensure the chain passes through it before determining the chain length. Then add two rivets to establish where you need to break the chain.

Close up shot of a wrapped bike chain.

Now You Know How To Determine Chain Length

The easiest way to determine chain length is to compare your new one with the old one, so don’t be so fast to throw it away!

But if you don’t have the old one, you don’t have to worry, and you can be back on the road with very little bother. Just follow the steps in this guide to chain length and check out our instructions on removing and replacing a bike chain, and you’ll be riding again in no time!

Found this Article Helpful? Develop your cycling knowledge Further With The BikeTips Experts’ Guides Below!

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One of BikeTips' regular content creators, Tom lives in the French Alps. When he isn't writing, he can be found charging downhill on a mountain bike or snowboard. Tom's other passion is fitness, which goes a long way to help him make the most of the Alpine lifestyle.

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