Chain Length Calculator
Determine the exact number of links needed for your drivetrain using the standard 'Riggs' approximation formula.
Bike Measurements
Center of BB to center of rear axle.
Count teeth on your biggest ring.
Count teeth on your biggest cassette cog.
Required Chain Length
Includes Quick-Link / Master Link. Always round to the nearest even number.
Why Chain Length Matters
Installing a chain with the wrong length is one of the most common mechanical errors. The chain must be long enough to safely wrap around your Largest Chainring and Largest Cog simultaneously (Big-Big combination) without ripping your derailleur off. Conversely, it must be short enough to maintain tension in the Small-Small combination so the chain doesn't sag or slap against the frame.
Full Suspension Warning
On full-suspension mountain bikes, the distance between the cranks and rear axle (chainstay length) often increases as the suspension compresses. You must measure the chainstay length at full compression (let all air out of the shock) to ensure the chain isn't too short when you hit a big bump.
The Math: Riggs Formula
This calculator uses the standard equation for derailleur chain sizing:
Length (Inches) = 2(Chainstay) + (Chainring/4 + Cog/4 + 1)
This result is then converted to "Links" (since one link is 1 inch, or strictly speaking two 0.5" pitch half-links).
Manual Method (Verification)
If you don't trust the math, you can use the physical sizing method:
- Shift the front derailleur to the Big Ring.
- Shift the rear to the Smallest Cog.
- Thread the chain through the derailleur.
- Check that the derailleur cage and pulleys are vertical (perpendicular to the ground).
Note: Modern 1x12 systems (SRAM Eagle / Shimano 12s) have very specific gap-tool methods. Always consult the manufacturer manual for 12-speed drivetrains.
Related Calculators
If you are changing your chain, you might be changing your cassette too. Check our Gear Ratio Calculator to see how a new cassette affects your climbing range.