Chain Length Calculator - Bike Chain Size in Inches and Links

A chain length calculator sizes a replacement bicycle chain from three drivetrain measurements: the chain stay length, the largest front chainring teeth, and the largest rear cog teeth. Riders use it when installing a fresh chain, switching to a different chainring or cassette, or building a bike from a frame and need to know how many links to cut before the chain breaker. Getting the chain length right keeps the rear derailleur spring tension within its safe range and lets the chain clear the largest front and rear gears with about an inch of slack.

• • Replacing a worn chain: Match a new chain to your frame and gearing when the old one has stretched past 0.5 percent wear.
• • Switching chainring or cassette: Recheck chain length whenever you change the largest front or rear gear to avoid a chain that is too short or too long.
• • Building a bike from a frame: Calculate the link count before cutting so a single-speed, fixed gear, or 1x build has the right chain on the first try.
• • Verifying a chain in the workshop: Confirm a chain breaker or quick-link installation has produced a safe length before test riding.

Most modern derailleur bicycles share a 0.5 inch chain pitch, so a chain length in inches maps cleanly to a whole number of links. Enter the chain stay, the largest chainring teeth on the crank, and the largest cog teeth on the cassette to see the result in inches, in links, and as the rigorous shortest possible length.

Once you know the right chain length, the Bike Gear Calculator shows the gear ratios for every chainring and cog combination on that same drivetrain.

The calculator applies the simple chain length equation to every input set and shows the rigorous equation alongside it so you can pick the safer number. The chain length in links is derived from the standard 0.5 inch chain pitch shared by almost every derailleur chain on the market today.

• C: Chain stay length in inches (distance from the bottom bracket center to the rear axle center).
• F: Tooth count on the largest front chainring you will ride.
• R: Tooth count on the largest rear cog your chain must wrap around.
• pitch: Standard chain pitch of 0.5 in used to convert length to links.

The simple equation is accurate for chain stays of 15 in or longer with normal road, gravel, and mountain bike gearing. For shorter chain stays or unusual gearing, the rigorous equation accounts for how the chain wraps around the gears and returns a slightly smaller minimum length.

Divide the simple-equation length by the 0.5 in pitch to convert inches to links, then round up so the chain ends on a full link. Most riders add one more link for the master link so both chain ends terminate with inner plates.

According to Park Tool, the workshop standard for sizing a new chain is to wrap it around the largest front chainring and the largest rear cog, then add two rivets (one inch) of slack to set the cutting point before joining the ends with a master link

With a freshly sized chain in place, the Bike Cadence Calculator turns the same chainring and cog teeth into pedal RPM at any riding speed.

Four terms come up every time you size a chain, and they each affect the answer in a different way. Get comfortable with these so you can sanity check any result the calculator gives you.

The simple equation assumes a chain stay of about 15 in or more and a normal difference between chainring and cog teeth. If your geometry is unusual, the rigorous equation returns a smaller theoretical minimum and gives you a safer comparison number.

If you want to see how the chainring and cog numbers in the calculator relate to gear inches and meters of development, the Bicycle Gear Ratio Calculator explains that side of the drivetrain.

Run the calculator in under a minute by measuring three numbers from your bike and reading the result panel. Each step here lines up with a field in the input form.

1. 1 Measure chain stay length in inches: Measure from the center of the bottom bracket to the center of the rear axle. Convert fractions to decimals (16 3/8 in becomes 16.375) and enter the value in the chain stay field.
2. 2 Count the largest front chainring teeth: Use the chainring you actually ride, not the largest one on a triple you never shift into. Read the tooth count off the crank or from the spec sheet.
3. 3 Count the largest rear cog teeth: Read the tooth count on the biggest cog of your cassette. The simple equation uses this number to add slack for the big-big combination.
4. 4 Read the chain length in inches and links: Open the results panel. The simple length is the safe size, the rigorous length is the theoretical minimum, and the links column is the number of links to cut at the standard 0.5 in pitch.
5. 5 Add one link for the master link: Use the recommended links value (links plus one) when you cut the chain so the master link can clamp onto two inner plates.

With a chain stay of 16.375 in, a 42-tooth chainring, and a 32-tooth cog, the calculator shows 52.25 in, 51.29 in, 105 links, and a recommended 106 links. Cut the chain to 106 links, install the master link on the inner plate pair, and verify about an inch of vertical slack in the lower run.

After the chain is cut and installed, the Bike Pace Calculator turns your cadence and chosen gear into a target pace per mile or kilometer.

Sizing a chain with the calculator is faster than measuring by hand and gives a reproducible answer you can share with a mechanic or riding partner. These benefits show up every time the chain gets replaced or the gearing changes.

• • Avoid a chain that is too short: A short chain binds the derailleur under load and can damage the hanger on a big gear.
• • Avoid a chain that is too long: An over-long chain flops between the chainring and cassette and can drop off the gears on rough terrain.
• • Get the right link count on the first cut: The link count is rounded up using the standard 0.5 in pitch, so the chain ends on the correct plate orientation for a master link.
• • Switch gearing without trial and error: Recheck the chain length whenever you swap the largest chainring or cassette cog.
• • Plan workshop time before the chain breaker comes out: Knowing the link count in advance means you only break the chain once.

Use the chain length calculator each time you replace a chain so the rear derailleur spring stays in its safe range and the chain clears every gear combination.

Once the chain is sized and the drivetrain runs cleanly through every gear, the Bike Speed Calculator turns the same chainring and cog teeth into mph and km/h once you add cadence and wheel size.

A handful of bike setup choices change the result enough to matter. Check these factors before you commit to a cut length on the workshop floor.

• • The simple equation assumes a chain stay of about 15 in or longer. For shorter chain stays or unusual gearing, the rigorous equation gives a smaller theoretical minimum.
• • Full suspension frames compress through the travel and need extra slack. The calculator does not include suspension travel, so add the frame travel in inches to the chain stay before computing.
• • Chains wear and stretch over time. Replace chains at 0.5 percent stretch, not when they only feel stiff.

This chain length calculator covers road, gravel, mountain, commuter, and many e-bike drivetrains. For Brompton or other compact folders with very short chain stays, add extra slack for the derailleur pulley travel.

According to Park Tool, routing a new chain around the largest front chainring and largest rear cog is the workshop standard for sizing a replacement bicycle chain

Chain stay length depends on frame size, so riders picking a new frame can use the Bike Size Calculator first and then come back to this calculator with the right chain stay number.