How do you measure bike size?

Depending on the type of bike, size is determined either by the size of its seat tube or top tube. To figure out the correct bike measurement, users must first determine if they are measuring a mountain/road bike or a BMX bike.

Mountain bikes and road bikes are measured in the exact same way: by determining the length of the bike's seat tube. This is the standard measurement for both types of bikes regardless of whether the tube is one continuous piece.

1. Identify the seat tube
Locate the top of the seat tube, namely the point where the seat's clamp holds the seat to the post. Next, locate the center of the bottom bracket, which is the point at which the pedals connect to the bike.
2. Measurement
Measure the distance between the two points in both centimeters and inches, rounded to the nearest half an inch for the latter. These numbers are the bike size.

BMX bikes, on the other hand, come in two frame styles: freestyle and racing. However, they are both measured in the same way, namely by determining the length of the top tube.

1. Find the top tube
The top tube is a long, cylindrical tube which sits between the head tube (handlebar) and the seat tube (saddle) of the bike.
2. Find the size
Measure the distance of the tube between those two points in both centimeters and inches, rounding to the nearest half an inch for the latter. This number is the bike size.