Bike frame size chart: what 54 cm, 17 inch and Medium mean in a used listing

One chart for used listings

Sellers copy whatever is printed on the frame, or guess. This chart puts the three systems side by side. The centimetre, inch and letter ranges are the ones Sift uses to read sizes in listings, and a sensible starting point for anyone.

Rider heights depend on the model. Two of Giant’s current charts show how much the ranges overlap and shift:

If you sit near the edge of two sizes, the maker’s chart for that model is the tiebreaker, and so is a test ride.

Road, gravel and hybrid bikes

A road size in centimetres usually means the length of the seat tube, measured from the centre of the bottom bracket. That made sense when every road frame had a level top tube. It means less now.

• Effective top tube is the horizontal distance from the head tube to the seat post. It tells you more about how stretched out you’ll be than the seat tube does.
• Stack and reach are how makers compare frames today: stack is how high the front of the bike is, reach is how far forward. Two 54 cm bikes can differ by a couple of centimetres in reach, which you’ll feel on every ride.
• Sloping top tubes blur the numbers. Giant’s Revolt 2 in medium has a 470 mm seat tube, which reads as “47 cm” and looks like an extra small on an old chart, yet it’s made for riders 169 to 181 cm tall.

Trek has moved its road bikes from numbered sizes to letters, and many brands have done the same. So a 2015 listing may say “56 cm” and a 2023 listing for a similar rider may say “M/L”. When a listing gives both a letter and a number, trust the letter and the model’s chart. Hybrids and commuter bikes are sold in letters or inches as often as in centimetres.

Mountain bikes

Older mountain bikes were sold by seat-tube length in inches: 15, 17, 19, 21. Modern frames have short seat tubes (so dropper posts fit) and much longer reach, so most brands switched to letters.

That’s why a 2012 “17 inch” and a 2024 “M” can fit very differently. Giant’s Yukon E+ fat bike in medium has a 420 mm (16.5 in) seat tube, which an older inch chart would call a small, and it’s sized for riders 169 to 179 cm. Read the inch size in an older listing as a rough guide, and look up the geometry for the model and year when you can.

Kids’ bikes are sized by wheel

Children’s bikes go by wheel diameter, from about 12 inches to 24 inches, not by frame. Giant’s youth chart, for example, puts a 20-inch wheel at riders 115 to 130 cm tall and a 24-inch wheel at 125 to 145 cm, and advises against choosing by age. Measure the child’s inseam and height instead.

Don’t confuse wheel size with frame size in adult listings either. “29er” and “27.5” are wheel sizes, and so is “700c”. None of them tells you the frame size. Sift doesn’t read wheel sizes, handlebar widths or rider heights as frame sizes for the same reason.

Checking fit at the meetup

You can’t book a fitting for a used bike, but you can check the basics in five minutes.

1. Standover. Stand over the top tube with both feet flat. You want clearance, and more of it on a mountain bike.
2. Saddle height. With the saddle set so your leg is almost straight at the bottom of the pedal stroke, check the seatpost isn’t past its minimum insertion line. If it is, the frame is too small for you.
3. Reach. Sit on it with your hands on the bars or hoods. You should reach them with a slight bend in your elbows, without locking your arms or hunching.
4. Test ride. Ride for a few minutes, out of the saddle as well as in it. Toe overlap with the front wheel, sore wrists or a cramped feeling are signs to keep looking.

Some things are cheap to change: saddle height and position, a shorter or longer stem, spacers under the stem, bars and grips. The frame isn’t. If it’s more than one size off, no stem will fix it.

Ask the seller

A one-line message saves a trip:

Hi, what size is the frame, and what’s printed on it? What model and year is it, and how tall are you?

The size is often printed on the seat tube or on a sticker near the bottom bracket. The seller’s height is a quick sanity check: a 190 cm seller riding an XS is possible, but worth a question. Canadian Cycling Magazine suggests asking how tall the previous owner was for exactly this reason.

Search by size on Marketplace and Kijiji

Facebook Marketplace has no frame-size filter, and size is rarely in a structured field on either site. What works:

• Add a size to your search: 54cm, 54 cm, medium, 17", size L. Try two or three spellings.
• Search the model name, then open the listings and look for the size in the text or photos.
• On Kijiji, choose the Bikes subcategory (road, mountain, kids’, e-bikes and others) first, so size words aren’t competing with exercise bikes and helmets.

The catch is that many listings never mention a size, and many mention it in a way search doesn’t match.

Filter listings by size with Sift

On a computer, Sift, a free browser extension for Facebook Marketplace and Kijiji, reads the size from the listing title and text and does the sorting for you.

• Options › Filters › Bikes: pick your sizes from XS to XL chips, and choose whether bikes with no readable size are shown or hidden.
• Hidden bikes keep their reason, such as “Frame size L” or “Frame size unknown”, so you can peek at them.
• The details card shows the size it read, such as “Bike · size M (54 cm)”. Inch frames stay in inches: “size L (19 in)”.
• It reads the formats in this chart: centimetres, inches, letters, words and French (petit, moyen, grand). Wheel sizes and rider heights aren’t mistaken for frame sizes.
• Start a hunt › Bike saves a preset with the size filter switched on (pick your sizes once) and the parts pack, which hides “for parts” listings.
• New-listing alerts pass through the size filter too, so you only hear about bikes in your sizes.

It works on Facebook Marketplace and Kijiji in Chrome, Edge and Brave on a computer, not in the phone apps. Sift is independent and not affiliated with Meta, Kijiji or any bike brand named here.

For the rest of the checks, see the used bike checklist.