# Bicycle frames

What’s proper way to measure the size of a bicycle frame? ie. when they say a bike is 18", is that a height? a length? a cross-wise measurement like TVs?

That’s the measurement of the central, vertical tube, from the crank housing to the top opening.

If only life were that simple Davebear! Your answer is basically right, but there are plenty of people who meausure things a bit differently. According to Sheldon Brown

The next question is why do you need to know? Because thae answer to that makes a big difference if you are trying to get a bike to fit you.

I’m trying to figure out what size my old bike is so that I can
a) sell it with the correct info
b) buy a new, bigger bike that fits me better.

It’s a Minelli, bought in 1995, if that’s any help.

Racing frames usually have the size stamped at the bottom and it’s usually in metric. I would measure the seat tube, from the the center of the bottom bracket to where the top tube meets the seat tube. Often times bike sizes are described by the size of the wheels 26", 27" as opposed to the frame size.

Yeah, most often, bicycles, when desribed in terms of it’s size, are measured using their wheel diameters - 16", 20", 24", etc.

But if you’re just going by the frame, as asked in the OP, I’ve always heard it measured by the length of the top tube. So yeah, as Tapioca Dextrin mentioned, I guess it varies.

Er, I don’t think I’ve ever seen the length of the top tube used, so I assume vandal mistyped (the top tube is the one that is missing/lower on a “girl’s” bike). I’d advise just using the traditional method of measuring from the center of the bottom bracket to the opening of the seat tube, since (in my opinion) the measured frame height just gives you an idea of how big the bike is, and you have to actually get on the bike in order to find out if it’s the right size for you anyway (due to varying frame geometries).

It’s also wrong to say that bikes are mostly measured using their wheel diameters. It’s a common way of classifying them, but frame sizes vary so much within a given class that it’s not very useful to advertise that you’re selling a 26 inch mountain bike.

Depending on where you live, one thing to consider is trading in your old bike at a bike shop. They should give you a fair price, plus you can get a new bike that fits you properly.

If you really want to get technical on frame fit, try this site:

Bicycle Size/ Proportions Analysis

It’s not a bad site, but if you really want to get a frame that fits, nothing beats getting on a bike-sizing machine. The guy in the second B&W picture with hands on hips is the guy that fitted me. We got a good size after maybe an hour. The only reason it was this quick is that I had my old custom built frame with me to use as a guide.

The bike is fit for a God. It isn’t ridden by one, however.