Trek Marlin Size Chart by Height and Inseam (Gen 3)

Trek sizes the Marlin by height, as of the Gen 3 Marlin:

• An XS fits 4’9″ to 5’1″,
• An S fits 5’1″ to 5’5″
• An M fits 5’5″ to 5’9″
• An ML fits 5’8″ to 5’11
• An L fits 5’10” to 6’2″
• And an XL fits 6’2″ to 6’5″

These ranges overlap on purpose, so in the rest of this article, we’ll talk about picking the right one when you sit on a line.

You’ll get the full chart with inseam, the frame numbers for each size, and a clear answer for the two spots where most buyers get stuck.

If you want a size for any mountain bike and not just a Marlin, you should check the mountain bike size calculator.

Trek Marlin size chart

This is Trek’s own sizing for the Gen 3 Marlin, which is the generation printed in the model name, like Marlin 5 Gen 3. Find your height first. Then check your inseam against the same row.

Size	Frame size	Rider height	Rider height (cm)	Inseam	Inseam (cm)	Wheel size
XS	14.5″	4’9″ – 5’1″	145 – 155	27 – 29″	69 – 73	27.5″
S	15.5″	5’1″ – 5’5″	155 – 165	29 – 31″	74 – 78	27.5″
M	17.5″	5’5″ – 5’9″	165 – 176	31 – 33″	79 – 83	29″
ML	18.5″	5’8″ – 5’11”	173 – 180	32 – 34″	81 – 86	29″
L	19.5″	5’10” – 6’2″	177 – 188	33 – 35″	84 – 89	29″
XL	21.5″	6’2″ – 6’5″	188 – 195	35 – 36″	89 – 91	29″
2XL	23″	6’5″ – 6’8″	195 – 203	36 – 38″	91 – 97	29″

Look at the wheel column, the Marlin changes from 27.5 inch wheels to 29 inch wheels between the S and the M, so a rider around 5’5″ is picking a wheel size as much as a frame size.

If you haven’t measured your inseam yet, do that before you trust the height column. The steps are in my mountain bike size calculator guide.

Trek Marlin geometry by size

Height will tell you the size Trek suggests, reach will tell you how the bike will feel once you’re on it.

These are the Gen 3 numbers from the Marlin 5, in millimeters.

Size	Seat tube	Reach	Stack	Standover
XS	340	390	563	658
S	370	415	572	692
M	420	440	609	747
ML	435	455	614	759
L	450	470	618	771
XL	500	495	637	791

Two things stand out: reach grows by 25 mm from S to M, then only 15 mm per step through ML and L.

Stack jumps 37 mm from S to M, which comes from the wheel change, so the M will feel taller up front than the S by a good margin.

Standover is fine on every size, even the XS, with the smallest gap, sits at least 3 cm under the bottom of Trek’s inseam range, and the bigger sizes leave 5 to 10 cm.

On the XS and S, Trek curves the top tube down to keep standover low.

Between two Marlin sizes: M, ML or L

The ML covers riders from 5’8″ to 5’11”, so four of the height ranges overlap, but the inseam settles each one.

Your height	Your inseam	Pick
5’5″	31″ or less	S
5’5″	32″ or more	M
5’8″ – 5’9″	32″ or less	M
5’8″ – 5’9″	33″ or more	ML
5’10” – 5’11”	34″ or less	ML
5’10” – 5’11”	35″ or more	L
6’2″	35″ or less	L
6’2″	36″ or more	XL

Two riders can both stand 5’9″ and have a 31-inch and a 34-inch inseam.

The first one belongs on the M, the second on the ML, and a height-only chart sends them both to the same bike.

If your arms are long or your torso is long for your height, go to the bigger size in your row.

You’ll have 15 to 25 mm more reach, and the bike will stop feeling cramped on flat, open trail. If you ride tight, steep climbs and want the front end to turn quickly, take the smaller one.

Don’t buy a size up to grow into it, because a frame that is too long will make you stretch for the bars, and you’ll feel it on every climb.

Handlebars and cranks change with the size

Trek have different parts on every frame. The Marlin 5 Gen 3 ships with 690 mm bars on the XS, 720 mm on the S, and 750 mm on the M and every size above it.

Cranks are 160 mm on the XS and 170 mm on the S through the XL, and the Marlin 6 adds a 175 mm option.

That 60 mm gap in bar width is why a small rider on a Marlin doesn’t have to fight a bar made for a 6-footer.

It’s also why you shouldn’t size down to an S just to get narrower bars. If you land on the M and 750 mm feels too wide, a shop can cut the bar ends down or swap in a narrower bar.

Stems and brakes change too. In Marlin 5 Gen 3 you get a 35 mm stem on the XS and S, a 50 mm stem on the M, ML and L, and a 60 mm stem on the XL.

The XS and S also get short-reach brake levers, which are easier to pull with small hands.

If you ride an M or ML and feel stretched out, the 50 mm stem is the first thing to try shortening.

Marlin 4, 5, 6 or 7: does the model change your size?

Actually not! The height ranges follow the same chart across the Gen 3 line.

What changes from model to model are the parts. The Marlin 4 and 5 have a 100 mm SR Suntour coil fork, the Marlin 7 has a RockShox air fork and a TranzX dropper, and the Marlin 6 and 7 come with dropper posts and tubeless-ready wheels.

You can also see my dropper post size guide.

Why the Marlin switches from 27.5 to 29 inch wheels

Trek calls it Smart Wheel Size, the XS and S roll on 27.5 inch wheels, and the M through the XXL roll on 29 inch wheels, as Flow describes it.

Trek’s pitch is that each frame gets the fastest wheel that fits it, and the fork follows the wheel: the Marlin 7 lists a 42 mm offset fork for the 27.5 inch sizes and a 46 mm offset fork for the 29 inch sizes.

This changed with the generation. On the 2022 Marlin, Cycles UK says the smallest bikes came with 26 inch wheels for riders from 4’5″ to 4’9″.

If you find a used Marlin with 26-inch wheels, it’s the older generation, and the Gen 3 chart above doesn’t apply to it.

For you, the wheel jump matters at 5’5″. The S at 5’5″ gets the quicker-turning 27.5 inch wheel and the M gets the 29 inch wheel that rolls over roots more smoothly.

Use the inseam table above to choose the frame, and let the wheel come with it.

A ten-minute fit check once your Marlin arrives

The chart will get you the right frame, but these checks will confirm the bike fits you:

1. Set the saddle height from your inseam. My mountain bike saddle height calculator shows how, and it’s the one adjustment that changes how every other part of the bike feels.
2. Make the saddle level. The saddle that tilts up or down changes how far you sit from the bars.
3. Stand on the pedals in your attack position, with your elbows bent (just a little) and your weight split between your hands and feet. If your arms are straight and you feel stretched, the cockpit is too long, so you need the shorter stem.
4. Check that you can pull each brake lever with one finger while your wrist stays straight. The XS and S come with short-reach levers for this reason.
5. Ride for ten minutes and change one thing at a time. If you move the saddle and the stem together, you won’t know which one helped.

Trek Marlin sizing FAQ

What size Trek Marlin for someone 5’10” tall?

An ML or an L, with an inseam of 34 inches or less take the ML, and at 35 inches or more take the L.

At 5’10” both sizes are inside Trek’s range, so the legs decide it.

What size Trek Marlin for a 6 foot rider?

An L, because it covers 5’10” to 6’2″ with a 470 mm reach. The XL doesn’t start until 6’2″ and is meant for inseams of 35 to 36 inches, so only the tallest 6 footers should look at it.

What size Trek Marlin for a 5’6″ rider?

An M. It covers 5’5″ to 5’9″ and comes with 29-inch wheels.

The S ends at 5’5″ and runs 27.5-inch wheels.

Is a Trek Marlin medium a 17.5 inch frame?

Yes, the Gen 3 sizes are XS 14.5″, S 15.5″, M 17.5″, ML 18.5″, L 19.5″ and XL 21.5″.

Do the Gen 2 and Gen 3 Marlin use the same sizes?

Actually, the size names match, but the frames don’t. Gen 2 reach runs from about 376 to 466 mm, while Gen 3 runs from 390 to 495 mm on XS through XL.

Therefore, you should check the generation in the model name and use that chart.

Does the Trek Marlin come with 26 inch wheels?

Not on Gen 3, XS and S have 27.5 inch wheels and the M and up have 29 inch wheels.

The 2022 Marlin put 26 inch wheels on its smallest size.

Which Trek Marlin has a dropper post?

The Marlin 6 and 7 both have droppers.

Should I size up or down on a Trek Marlin?

Size up for stability at speed and more room if your arms are long.

Size down for a bike that turns quicker. Use the inseam table above to decide at the four height overlaps.