How to Size a Bicycle Chain the Right Length

There are a lot of important things that cyclists should know. One of such things is how to size a bicycle chain. You can’t ride your bicycle if it doesn’t have a chain. The chain is the key mechanism behind your bike’s mobility.

However, because of how much work the chain does, it’s prone to certain friction-related damages. When you’ve been riding the bike for a considerable amount of time, the chain begins to slack and lose its firm grip.

The proper length specification of your bike’s chain should be 12-inch per 12 chain links. However, if yours starts measuring 12 1/16-in per 12 chain links there’s a problem. With such a measurement, you’ll need to get a new chain.

How to Size a New Chain for a Bicycle

There are steps to follow when you want to size your bike’s chain. If the replacement chain you get isn’t in the right length, it won’t work for your bike.

1. Count the Links of Your Old Chain

The first thing you need to do when you size a new chain for a bicycle is measuring the needed length of the replacement one with respect to the old chain.

To do this, you need to ensure that the former chain is still accurately sized. Engage the littlest sprockets on your bicycle and observe if the chain fits firmly or not. If it doesn’t, then the old chain isn’t sized correctly.

After making that observation, you’ll need to engage the biggest forward and back sprockets. If the chain is correctly sized, there shouldn’t be any problem moving to the biggest sprockets.

If everything looks good, you can proceed to the next step. This involves taking off the chain and spreading it upon the bare floor.

If you don’t want to visually observe/compare the lengths of the former chain to the replacement chain, you can just count the number of links the former chain has, and customize the replacement chain based on that.

2. Try the Chainring Method

This technique is another great tip on how to determine bike chain length:

  • First, take off the old bike chain. After that, switch the derailleurs with respect to the biggest and littlest chainrings. The one in front goes to the former and the one behind the latter.
  • Now, the replacement chain has to be placed on the biggest chainring.
  • As you position the replacement chain on the biggest chainring (in front), make sure that it goes through the leading derailleur cage.
  • Keep the chain in a 150⁰ position.
  • For those with a master link, set up half of the master link around the foremost part of the chain.
  • With the bottom end of the stug in hand, drag it in the direction of the foremost chain.
  • At the nearest merging points, add an extra pair of links.

3. Use the Chain Sizing Equation

Another applicable technique that will help you size a bicycle chain is by using the equation.

With this technique, you don’t need to unpack the replacement chain from its container before you can do the chain sizing.

Frequently Asked Questions

How do I know my bike chain size?

To know your bike chain size, start by counting the number of teeth found on the biggest sprockets both at the foremost end and backside of the bike. After that, calculate the chainstay distance.

How long should my bike chain be?

The length specification of the back axle midpoint to the crank bolt’s midpoint is 16-3/8″.

Do bike chains stretch?

The thing is that bike chains don’t actually stretch. What happens is that the chains get worked up for a prolonged period of time until their original length changes. This effect makes the chain sag instead of holding firmly in its position.

How do I measure my bike chain for stretch?

The expected specification is 12 inch per 12 links. If there’s as much as a percent increase in the original chain length, then the chain is said to have slacked. However, changing the chain before it gets that slack is encouraged.

How do you tell if your chain is stretched?

Rulers are a useful tool for telling if the chain is slacked or not. From one rivet, align it to 0 on the ruler. Measure the next 23 rivets and expect to have the last one aligned with the ruler’s 12″ point. A bad slack would be indicated by a 1/16″ increase in the original length.

What size chain do I need for a 21-speed bike?

After counting the number of cogs attached to the back hub, you can tell how long the replacement chain should be. This works for bikes that have derailleurs. Usually, they have a 3/32″ specification. This means that your best options are 5/6/7-speed, 8-speed, 9-speed, or 10-speed chains.

Is my bike chain too short?

A chain length that isn’t long enough would cause the derailleur cage to be overly extended. At this point, engage the littlest chainring and the littlest cog. If the derailleur at the back end drags the chain until it touches itself, the length is excessive.

How long does a bicycle chain last?

You can expect it to serve you from around 500 to 5,000 miles. Different chains have different lasting periods, and their lifespan is affected by the intensity of your riding exercises.

How often should a bike chain be replaced?

If you don’t want the cassette and chainrings to slack badly, it’s best to dispose of them before they get too old. After the chains have been exposed to as much as 2,000 miles of cycling, you should switch them with newer ones. Note that 2,000 miles isn’t the perfect figure for everybody. Just make sure you’re observant of the changes in your own bike chain.

Are bike chains universal?

No, bike chains aren’t universal. Although the teeth of sprockets have a similar 1 ½ inch design, you still can’t use one bike chain as a replacement for any other chain. Take note of the main bicycle chains you’ll come across. They are one-speed and derailleur chains.

How much do bike chains cost?

Depending on your available budget you can get a bike chain for as low as $10. The more expensive ones cost about $90. Different bicycle models would require a certain type and quality of a bike chain. This factor also affects the cost of purchasing a replacement chain. Just make sure you purchase one that satisfies your needs.


Like said in the introduction, there are a lot of important things that cyclists should know. One of such things is how to size a bicycle chain properly.

The chain is such an important part of the bicycle. It’s the major mechanism behind your bike’s mobility. However, because of how much work the chain does, it’s prone to certain friction-related damages.

When you’ve been riding the bike for a considerable amount of time, the chain begins to slack and lose its firm grip.

This is why we have put this article together. Follow the tips and instructions to learn how to easily size your bike’s chain. Drop a comment down below if you need help with anything!

James Mattis

James is a passionate bicyclist who has done about every kind of biking there is. He loves the wind in his hair, the sun over his shoulder and maybe even the bugs in his teeth. No, just kidding about that last item. He isn’t crazy about road burns, either, but acknowledges that to have the good there is the occasional tumble. James feels that his bike is the place where he can unwind, leave troubles alongside the road, meet new people, go new places, and live the life of adventure that he loves. He is ready to share the ride with you.

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