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Chain Length Calculator

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Why is bicycle chain length significant? 🚴What size bike chain do I need?How to measure a bike chain lengthHow do we calculate bicycle chain length? Bike chain size formulaHow chain size calculator works? Tips and trickstl;dr: How to size a bike chainFAQs

This chain length calculator will help you determine the required chain length for your bicycle. We all know that there are many ways to calculate bicycle chain length, for example, by comparing it to a reference chain. But what if you do not have a reference at hand? Well then, we're sure that this bike chain length calculator will come in handy! In this article, you will also learn about bike chain sizes

Why is bicycle chain length significant? 🚴

The bike chain is a crucial component when propelling a bike. It consists of inner and outer plates that are held together with rivets. Many standards exist for bicycle sizes, being specially designed for different transmissions and groupsets. In particular, the width of your bike chain is very important when equipping a 7, 8, 9, 10... or even 13-speed bicycle. If the number of gears at the back (the number of cogs on your rear wheel) increases, the width of your chain must decrease so as not to rub on the cogs, which will be closer together the bigger the number of "speeds".

Bike chains are metal-on-metal, which makes them tough and durable, but they are not unbreakable. If your chain gets worn or damaged, it could lead to less smooth riding and even wear down the rest of the components in your transmission. Likewise, a poorly sized chain can cause trouble. If you install a chain that's too long for your bike, it could flop around and drop off your cogs. A chain that's too short will increase the wear in the rest of your drivetrain and can also prevent you from using all the different gears your bike has.

💡 If you'd like to learn how to determine the bike speed, then you might want to take a look at the bike speed calculator and the bike gear calculator.

What size bike chain do I need?

Unfortunately, there isn't a universal bike chain that fits all bikes. Bike chain sizes vary based on several factors, and it is as important as bicycle chain length. If you are asking questions like "What size bike chain do I need?", the table below shows the most commonly used bike chain sizes:

# of rear sprockets

External width

Internal width

5-6-7-8 speed



9 speed

1/4" - 9/32"


10 speed

1/4" - 9/32"


10 speed narrow



11 speed



12 speed



🔍Did you know?
Almost all bike chains use the same pitch (distance between rivets) of 1/2 in. This means that the main distinction between bicycle chain types is the width!

If you are using a single-speed bicycle, you can technically use any chain, but the best choice would be to opt for a "single-speed chain", which should have an internal width of 1/8″ (3.175 mm) with the external width not being crucial.

How to measure a bike chain length

There are three ways to measure the chain length of a bike:

1. You can use your original chain as a reference to find the required bike chain size.

2. Buy an uncut chain (standard length should work for most bikes) and use the largest front chainring and largest cog to find the maximum required chain length for your bike.

3. You can calculate the bike chain length with a chain length calculator.

While calculating the bicycle's chain length, it is essential to know the names of the chain-related parts of a bicycle. Basically, the following parts of a bike are important for a chain length calculator:

⚠️ When talking about chain length in terms of the number of links, there is no consensus. Technically, a link includes a narrow and a wide section, but most people, including us, will refer to a link as the pieces between two rivets.

Key components of the chain-related parts of a bicycle.
  1. Chain stay — the length between the center of the bottom bracket and the center of the rear wheel's axle.

  2. Front chainring — located in the middle of the bicycle, it is attached to cranks (the arms to which you attach the pedals) and the bottom bracket (the central bearing location around which you pedal).

  3. Cassette — it's the collection of cogs at the back, attached to the center of the rear wheel. In old and entry-level bicycles, it is sometimes called the freewheel; while not exactly the same, the differences don't matter when sizing up a chain.

  4. Rear derailleur — It's the mechanical actuator that allows your bike to change which rear cog is engaged, making it easier or harder to pedal and, therefore, making you move slower or faster.

Most bikes also have a front derailleur (which allows you to shift which front chainring is engaged), but these are not important when calculating the size of your chain.

💡 Some chains have different connecting methods for rejoining them after "cutting" them to size. The most common is the connecting link, which is almost toolless; old bikes use a standard pin that you had to press in with your chain breaker tool.

How do we calculate bicycle chain length? Bike chain size formula

In our chain length calculator, we use two different equations to calculate bike chain length. One of them is called the simple equation and is valid for chain stay length (C) greater than 15 inches and for bikes with standard front chainring or rear cog size, which is the following formula:

L = 2 × C + F/4 + R/4 + 1


  • LBike chain length in inches;
  • CChain stay length in inches;
  • FNumber of teeth on the largest front chainring; and
  • RNumber of teeth on the largest rear cog.

We also have another formula for calculating chain length called the rigorous equation. This equation is more accurate for bikes with a chain stay length (C) of less than 15 inches. We can also use the rigorous equation for bikes with a large front chainring and a smaller rear cog. If you have a bicycle like this, you should calculate your chain length with the following equation:

TSPCL = 2 × √(C² + (0.0796 × (F - R))²) + (F + R)/4


  • TSPCLTheoretical shortest possible chain length in inches;
  • CChain stay length in inches;
  • FNumber of teeth on the largest front chainring; and
  • RNumber of teeth on the largest rear cog.

Our chain length calculator gives you the result of both the simple and the rigorous equations in the fields "Chain length" and "Shortest possible chain length", respectively.

Unfortunately, this is not the end of the journey; chains cannot be cut to arbitrary lengths, as you always need to have an even number of links. That's why the most useful unit of your bike's chain length is the number of links. It can be easily calculated using the equation:

#_links = ceil(chain_length / link_length)

where chain_length and link_length must be in the same units, and the function ceil means you take whatever number comes out and round it up.

Don't worry if this seems too involved. Our bike chain size calculator does all this work for you, too!

How chain size calculator works? Tips and tricks

When we want to calculate the bicycle's chain length, we should first convert fractional inches to decimal inches. We generally use this conversion for the chain stay length (C) part of the chain size formula. The table below gives the decimal of each fractional inch measurement:

Fractional inches

Decimal inches















🙋 Example: Using the simple equation, let's calculate the chain length of a bike with a 42-32-22 front chainring. The cassette has 32 teeth on the largest cog, and the chain stay length is 16 and 3/8".

  1. Looking at the table above, we should convert the chain stay length from a fraction to a decimal. 16 and 3/8" equals 16.375" in decimal.

  2. We have 42-32-22 front chainring. We should always consider the largest one, so we will take 42 into account.

  3. We know the largest amount of teeth on the rear cog, which is 32.

  4. Apply these values to the bicycle chain length formula.

    L = 2 × 16.375 + 42 / 4 + 32 / 4 + 1

  5. Our chain length becomes 52.25 inches. Since it is virtually impossible a chain of that exact length (there are no fractional links), we need to convert the length to the number of links and round them up:

    #_links = chain_length / link_length
    52.25 in / 0.5 in = 104.5 links -> 105 link

  6. Our chain needs to have at least 105 links. Since chains need to match an inner plate with an outer plate and connecting links are only outer links, you might need to add one or two to the final length. Just don't forget to take into account the connecting link when sizing your chain!

💡 When converting from length to number of links, if the result is a decimal number of links, always round up. This way, if the calculations say you need 112.8 links, you should have at least 113; if it calculates 109.1 links, use at least 110 links.

  • If we use the rigorous equation for this case, the chain length calculator outputs 51 inches!

Now that you have learned how our chain length calculator works and how to measure a bike's chain length, you are ready for a bike trip! Check our other calculators for cyclists, such as the biking life gain calculator, the calories burned biking calculator, or the car vs. bike calculator.

tl;dr: How to size a bike chain

You need a new chain, and you don't have time to learn about measurements and standards... what do you do? Very simple: count the number of cogs at the rear and buy a chain rated for that number of gears or speeds. In a pinch, you can use a chain designed for a higher number of speeds, but not the other way around; it goes without saying that this is not ideal, and we recommend you always get the correct chain when possible.

Good. We have sorted the width of the chain; now, we tackle the length. If you still have the old chain, compare it and cut it to the correct size. Remember that chains elongate ("stretch") with time, so ensure you have the same number of links as the old one, not the same length.

If you don't have the old chain lying around, you could use the method described in the section How to measure a bike chain length. Still, the fastest way to calculate it is to use the bike chain length calculator to the right of this text; just remember to focus on the number of links more than the length.

Now, it's on to "cutting" the chain; breaking it would be a more appropriate term. For that, all you need is a chain breaker tool and a rejoinable link (sometimes called master links, quick links, or some other term, depending on the brand). Just make sure it's the correct link for the number of speeds your chain is rated for. When breaking the chain, you have to remember to count the master link in your calculations. Also, remember that a quick link is designed to join two inner links (the narrower ones), so you must break the chain so that both ends are terminated in inner plates.

Finally, install the chain and go on your merry way!


What's chain length for 15" chain stay length, 40 front teeth, 30 rear teeth?

The chain length will be 49 inches. You can calculate it using this formula:

chain length = 2 × (chain stay length) + (# front teeth) / 4 + (# rear teeth) /4 + 1

How can I calculate the chain length for my bike?

You can calculate the chain length in steps:

  1. Determine the chain stay length.

  2. Count the number of teeth of the largest front chainring; it might also be stamped on it.

  3. Count the number of teeth of the largest rear cog; it might also be stamped on it.

  4. Apply the chain length formula:

    chain length = 2 × (chain stay length) + (# front teeth) / 4 + (# rear teeth) /4 + 1

Can I shorten a bike chain that's too long?

Yes, you can shorten a bike chain by removing links with a chain tool. Always refer to the manufacturer's guidelines before doing so.

Does chain length affect gear shifting?

Yes, it does. Improper chain length can lead to poor shifting performance and may also put excessive stress on the rear derailleur.

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