Sizing and Fitting Kids Bikes

Bike Sizes

Kids bikes are called by wheel sizes, the sizes below are for Trek kids bikes, Electra kids run just a tad bigger

12 in wheeled bikes generally fit kids 34-40 inches tall

16in, wheeled bikes generally fit kids 39-46 inches tall

20in, wheeled bikes generally fit kids 45-52 inches tall

24, wheeled bikes generally fit kids 50-63 inches tall

26, wheeled bikes generally fit kids 53-66 inches tall

As they move to adult bicycles, the bicycles are measured by frame size and as they get taller they also get longer, each manufacture gets to determine where these points are measured from, with Trek Bicycles, mtn bikes start at 13in and go to 23in tall.   Hybrid / fitness / dual sport bikes start at 13in and go to 25in. Road / Crossbikes start at 44cm and go to 64cm.

Each category of bicycles will fit a bit different depending on, design, geometry, tire size, intended posture positioning, etc, we are here to help you choose the right size

See our Kids Bike Trade Up Program 

Basic Kids Bike Fit

Basic 12in-24in Fitting

With younger kids who are still developing the necessary skills to ride a bicycle like balance, cognitive thinking, hand strength and that are fitting bicycles in the 12-24in wheel range, we generally recommend that they can stand over the bicycle flatfooted and not be feeling pressure from the top bar of the bicycle, kids often will be more comfortable with being able to get at least both toes  to touch the ground while setting on the seat.  Often once they have ridden the   awhile and are comfortable with the bike you can raise the seat a bit to give them more leg extension so they have a slight bend in knee at bottom of pedal stroke

We interact the bicycle on 5 contact points; Hands, feet and seat.

These are important to support the rider in a safe and comfortable position.

With kids, smaller hands need smaller grips to have control

The length of the crank arm is matched to the size of the bike and are portioned to the size of the rider  on the 12in and 16in bikes , on  most of Treks 20in and 24in models they have  crank arm that  have  adjustable length  to accommodate growth of the riders legs  while they are in that size .

 Saddle on a trek 20in Precaliber 

Sweet Ride Electra kids saddle 

Saddles kids saddles on the Trek & Electra bikes are designed for the smaller pelvic shapes of children the shape and padding are set for the size and approximate posture positioning.


NOTE:  See saddles in the advanced kids fit section for more information on kids saddle fit and pay attention if you have fast growing kids.


Advanced Kids Fitting

As a parent that specializes in Bicycle fitting, and having a store that happens to sell quite a number of children’s bikes I have a few thoughts on more advanced kids bike fit.

Kids are a bit unique from a fit sense, on the positive side their bodies are often more flexible , lighter and more balanced in muscle composition,  on the more challenging side they are growing , this means the muscular and skeletal structures are changing and sometimes very rapidly , this can cause, muscles,  ligaments and tendons to have a hard time keeping up with bone growth  resulting in flexibility imbalances , boney areas with less tissue covering them and sometimes joint pain , (see saddles below)

The distance and time in the saddle is directly proportional to how exact the bike fit needs to be.

General riding around the neighborhood for most kids if they can safely get on and off the bike and have their feet touching the ground to whatever degree they are comfortable with, they are fine.

For rides like from Pullman to Moscow and back generally if they are comfortable to have just their toes touch the ground when coming to a stop or can come forward off the saddle and put a foot down, the seat height should be high enough that they have a slight bend in the knee at the bottom of the pedal stroke.

For those kids whose parents are taking them on longer distance rides, their fit on the bike should set so they are supported like that of a well fitted adult bike.


This the a main contact point on a bike , if a child is complaining about seat comfort pay attention ,  due to their bodies changing quickly the fit on the bike may be incorrect   this can result in excess pressure on soft tissue on the front of the saddle , for example a child who adds multiple inches in a short period of time  especially if it in the lower body can end up with tight hamstrings due to the bones growing faster than the ligaments , tendons and muscles can keep up with , this can cause low back soreness and excess pressure on the front of the saddle  , by changing the fit on the bicycle and saddle shape we can aviate the discomfort .

Bodies are like snowflakes no two are alike and when it comes to pelvis structures being supported on the saddle there are lot of variables involved, bone shape and size, placement of nerves and artery’s, tissue shape and muscle composition, flexibility, femur head angle, etc.  these all affect the appropriate saddle shape and with kids it’s changing due to growth.  If your child is on the correct size of bike and experiencing saddle discomfort, we have many different saddle shapes in stock (167 at last count) if they can give us some idea of where the saddle hurting them by pointing on saddle where they are feeling pressure we can often pick a saddle that will be a better fit, most saddles we sell have comfort guaranty so if we guess wrong bring it back.

Cycling shorts have extra padding designed for cushioning and reducing fiction on the contact area between body and saddle

we do offer bicycle fitting services along a very advanced suite of cycling analysis tools including saddle pressure mapping technology that are available if the child is experiencing more complex saddle issues.

Solutions for fit problems