What Size Is A Bike Chain? | Quick Fit Guide

You typed what size is a bike chain? because you want a clear spec you can act on, fast. Here’s a plain answer, then the detail: all current bicycle chains share the same pitch, 1/2 inch from pin to pin. The differences that matter are inside width and outside width. Inside width aligns to use case: 3/32" for multi-gear derailleur bikes, 1/8" for single-speed, hub-gear, track, and many BMX setups. Outside width aligns to the number of cogs on the back wheel: 6–8, 9, 10, 11, 12, or 13 speed. That’s the size choice in a nutshell.

What Size Is A Bike Chain?

Here’s the quick way to choose the right chain size for your drivetrain. Use the table to match your bike type and cassette speed. If in doubt, read the box on your current chain or count the rear cogs. This removes guesswork and keeps shifting clean.

Drivetrain Type	Chain Spec	Notes
Single-Speed / Track / BMX	1/2" pitch, 1/8" inner	Wide and sturdy; mates to 1/8" sprockets and rings.
Hub-Gear (Nexus, Alfine, Sturmey)	1/2" pitch, 1/8" inner (some 3/32")	Most use 1/8"; check your cogs if unsure.
6/7/8-Speed Derailleur	1/2" pitch, 3/32" inner; ~7.0 mm outer	Often sold as “6/7/8-speed.”
9-Speed Derailleur	1/2" pitch, ~11/128" inner; ~6.5–7.0 mm outer	Narrower than 8-speed; marked “9-speed.”
10-Speed Derailleur	1/2" pitch, ~11/128" inner; ~6.0 mm outer	Plate shaping matched to brand cassettes.
11-Speed Derailleur	1/2" pitch, ~11/128" inner; ~5.5 mm outer	Narrow plates; use matching quick-link.
12-Speed MTB / Road	1/2" pitch, ~11/128" inner; ~5.2–5.3 mm outer	Some road chains use “flat-top” plates.
13-Speed Gravel (Campagnolo Ekar)	1/2" pitch, ~11/128" inner; ~4.9 mm outer	System-specific; match brand and speed.

Bike Chain Dimensions Explained

Pitch: The Constant 1/2-Inch

Pitch is the distance between pins. Modern bicycle chains use a 1/2-inch pitch that matches modern cogs and chainrings. This standard traces to industrial roller chain and is shared across brands.

Inner Width: 1/8" Vs 3/32" Vs 11/128"

Inner width is the space between inner plates. Single-speed and most hub-gear bikes run 1/8". Derailleur systems run narrower. Older 5–8 speed setups use 3/32". Newer 9–13 speed chains use about 11/128" inner width to clear tightly spaced cogs.

Outer Width: Matched To Rear Speed

Outer width is the plate-to-plate distance at the rivet heads. As cassette cog counts rise, outer width shrinks so the chain won’t rub adjacent cogs. That’s why a 12-speed chain is slimmer than 9-speed though both share 1/2-inch pitch.

Can I Mix Chains Across Speeds?

Short answer: match the chain to the cassette speed. A 9-speed chain on an 8-speed cassette can work in a pinch, but shift feel can drop. The reverse (wide chain on a narrow cassette) can cause rub and mis-shifts. For single-speed or track, stick with 1/8" unless your cogs and ring are 3/32".

Close Variant: What Bike Chain Size Do I Need For My Drivetrain?

This section gives a step-by-step check so you can buy once and ride happy.

Step 1: Count The Rear Cogs

Check the cassette or freewheel. Count the distinct sprockets. That number sets your chain family: 6/7/8, 9, 10, 11, 12, or 13.

Step 2: Check Single-Speed Vs Derailleur

If your bike has no derailleur, you likely want a 1/8" chain. Many fixed-gear and BMX riders prefer that wider fit. Some single-speed builds use 3/32" parts; match the cogs and chainring.

Step 3: Read The Current Chain

Many chains print “10-speed” or similar on the side plates. If you can still read it, you’re set. If not, use steps 1 and 2.

Step 4: Pick A Brand And Link Type

Most riders now use master links (“quick links”). Get the right size link for your chain speed and brand family. Keep a spare in your tool wrap.

Step 5: Measure If You Found A Loose Chain

No label? Grab calipers and read the outer width over the rivets, or hold the chain next to a ruler and confirm the 1/2-inch pitch over several links. Compare to the width ranges later in this guide. That ID step saves a trip.

Chain Length: Picking The Right Number Of Links

Two things decide length: frame size and gear range. New chains ship long, usually 114–126 links. You trim with a chain tool or remove links before closing the quick link. On derailleur bikes, use the big-ring/big-cog sizing method, then add one inner-outer pair. On single-speed and hub-gear bikes, slide the wheel in the dropouts or use a half-link to dial chain tension.

For a full walkthrough with photos and the big-ring/big-cog rule, see the Park Tool chain length guide. It’s a clear step list that matches what mechanics do on the stand.

Brand And Model Quirks That Affect Fit

Chains with the same speed rating can still carry brand traits. Shimano labels some road chains as HG+ with shaped inner plates to aid upshifts; they expect a matching cassette and chainrings for best feel. SRAM road 12-speed uses a “FlatTop” profile with taller side plates and a matching quick-link; that shape trims weight and keeps stiffness with narrow outer width. Campagnolo drivetrains often ride best with chains from the same brand, partly due to chamfers and pin peening methods. Mix-and-match can work, yet staying within a brand family often keeps shifts crisp.

Direction arrows also matter. Some chains are directional, with an outer plate that faces outboard. Flip that, and shift timing can feel dull. Quick-links can be directional too. Check the tiny arrows before you snap the link closed.

Finally, ring tooth shape can steer your choice. Narrow-wide chainrings, common on 1x setups, hold the chain using alternating tooth thickness. They play best with the chain speed and brand the ring was designed around. If you move to a different brand family, test shift feel under pedaling load before a big ride.

Reference Specs Backed By Trusted Sources

Bicycle chains use 1/2" pitch. Inner width splits between 1/8" for single-speed and narrower sizes for derailleurs. Outer width shrinks as speed count rises. You can verify these specs in two long-standing references riders rely on: the Park Tool chain compatibility page and Sheldon Brown’s chain glossary.

Typical Outer Width By Speed

Use this chart when you’re trying to ID a loose chain or sanity-check a spec sheet. Values are common ranges from mainstream brands.

Cassette Speed	Typical Outer Width	Notes
6/7/8	~7.0 mm	Often sold as one group.
9	~6.5–7.0 mm	Wider than 10/11/12.
10	~6.0 mm	Plate shaping differs by brand.
11	~5.5 mm	Slim plates.
12	~5.2–5.3 mm	Ultra slim; road vs MTB quirks.
13	~4.9 mm	Campagnolo Ekar.

Common Mistakes That Lead To Poor Shifts

Ordering The Wrong Width

This shows up when a 6/7/8-speed chain is fitted to a 10-speed cassette. The chain rubs, the derailleur chatters, and the bike never feels quiet. Match the speed on the box to the cassette.

Mixing Old Parts And New Parts

A worn cassette paired with a new chain can skip under load. If your chain checker reads past the wear line and your cassette teeth look hooked, swap both. Fresh chain on a worn cassette eats both fast.

Skipping The Quick-Link Direction

Some links have arrows. Snap it the wrong way and you invite noise and ghost shifts. Take ten seconds and look for the tiny marks.

Buying Checklist So You Get The Right Chain First Try

Match Pitch And Width

Pitch is set at 1/2 inch. Width is your only call: 1/8" for single-speed and the speed-matched outer width for derailleurs.

Confirm Speed On The Box

Look for “8-speed,” “10-speed,” and so on. Cross-brand use is common, but match the speed rating.

Quick-Link Compatibility

Carry a spare quick-link that matches both brand family and speed. Some links are single-use; others can be opened and closed for service.

Lube Choice And Care

Pick a wet, dry, or ceramic lube that suits your weather and terrain. Clean, re-lube, and wipe the side plates; grit chews through pins and rollers. A clean chain keeps the same size longer and protects your cassette and rings.

From Specs To Checkout

You came here wondering what size is a bike chain? Now you can name the pieces: 1/2-inch pitch across the board, 1/8" inner for single-speed, narrower inner for derailleurs, and an outer width that tracks the cassette speed. With that, buying the correct chain is a two-minute task at any shop or online cart.