Bicycle Sizes for Kids: How to Buy and Measure a Kids' Bike

Choosing the proper bicycle size reduces the risk of injury and gives your child the confidence to cruise on two wheels. Here, experts share how to measure a kids' bike properly.

An image of a mom riding bikes with her daughter.
Photo: Getty Images.

Learning to ride a bike is not only a rite of passage for kids, but a passport to worlds beyond the front lawn. It's a healthy pastime that promotes strength, balance, and overall fitness. But before embarking on neighborhood cruises, your child needs a bike that suits their physical needs and personal taste. Follow this bicycle buying guide to learn about sizing, measurements, and more.

Where to Buy Kids' Bikes

Kids' bikes start at around $100 at most bike shops, compared to $50 and up at discount department stores. Cheaper models, however, tend to be heavier and more prone to mechanical problems, says Jay Townley, executive director of the Bicycle Council, a Wisconsin-based biking-industry association. Townley also notes that bike shops have more personalized services than general department stores—and they usually offer a free 30-day "checkup" to ensure that everything is functioning properly.

Let your child choose the color and style of the bike, while you decide on more substantial matters, such as size and quality. It's important that a child likes their bike so they're more inclined to ride it, notes Peter Moe of Washington, D.C.-based National Center for Bicycling and Walking, a leading bike-advocacy organization.

How to Measure Bike Size for Kids

Determining the correct bicycle size is crucial to your child's safety, especially since both oversized and undersized bikes can be hazardous. Too-big bikes, for instance, can prevent a child's feet from touching the ground and their hands from reaching the hand brakes. Too-small bikes, on the other hand, force a child to awkwardly pedal with bent knees, leading to joint pain and tired legs. Here's everything you need to know:

What Should I Measure?

Child bike sizes are determined based on wheel diameter. They generally range from 12 to 26 inches; larger wheel size correlates with larger bike frames. That said, parents should not choose a bike based solely on the wheel diameter, because the fit can vary widely between companies.

The best way to determine bicycle size is actually measuring your child's inseam and comparing it to the bike seat height. (To find their inseam, have your child stand against the wall wearing shoes. Measure the length between the crotch seam of their pants to the floor, where their pants end). The child's height and age might also come into play. (To find their height, have them stand against the wall and measure from the top of their head to the floor).

Kids' Bike Size Guide

Use the chart below to narrow down the correct wheel size based on your child's inseam, height, and age. If their measurements correlate with multiple different wheel sizes, choose the larger option because it gives room for growth (and it's also more stable to boot).

Child's Inseam: About 14 to 17 inches
Child's Age: 2-3 years old
Child's Height: 2'10"–3'4"
Wheel Size: 12 inches

Child's Inseam: About 16 to 20 inches
Child's Age: 3–4 years old
Child's Height: 3'1"–3'7"
Wheel Size: 14 inches

Child's Inseam: About 18 to 22 inches
Child's Age: 4–5 years old
Child's Height: 3'7"–4'0"
Wheel Size: 16 inches

Child's Inseam: About 22 to 25 inches
Child's Age: 5–8 years old
Child's Height: 4'0"–4'5"
Wheel Size: 20 inches

Child's Inseam: About 24 to 28 inches
Child's Age: 8–11 years old
Child's Height: 4'5"–4'9"
Wheel Size: 24 inches

Child's Inseam: About 26 inches and over
Child's Age: 11+ years old
Child's Height: 4'9"+
Wheel Size: 26 inches

Note that bike size measurement guidelines differ by brand; look at the manufacturer's website or ask a consultant for more accurate sizing.

Comparing Types of Kids' Bikes

You also need to consider the type of bike your child needs when determining proper sizing. Here's a look at the different options:

Balance Bike: Made without pedals, balance bikes help your child build confidence for riding. Aim to have your child's knees slightly bent or mostly straight, with their feet flat on the ground, while seated. The seat height will be equivalent to—or slightly below—your child's inseam measurement.

Pedal Bike With Training Wheels: The training-wheels phase may last a couple of months or a couple of years, depending on the rate at which a child's coordination and strength develop. Since your little one will need some stability, their feet should be flat on the ground while seated—although confident kids might feel comfortable on slight tip toes.

First Pedal Bike Without Training Wheels: A child's first two-wheeler should be a one-speed with foot brakes. They won't be ready for hand brakes and gears until their hands grow and strengthen. When seated on the bike, the heels of your child's feet can be flat on the ground, or a maximum of 1 to 2 inches off the ground. The seat height will depend on their comfort level; just make sure they can easily brake with their feet.

Second Pedal Bike Without Training Wheels: Once your child is ready for a larger bike with gears and hand brakes, they can upgrade to a multi-speed pedal bike. Their heels should be 2 to 3 inches off the ground while seated. To achieve this tip-toe position, the bike seat height will be a few inches above your kid's inseam measurement.

Remember that the bike seat can be raised gradually as your child grows; therefore, it's best to choose a bicycle that works for your child at its minimum seat height.

Also make sure your little one can comfortably stand over the top tube (the piece of frame between the handlebars and seat) to prevent injury. Their crotch should be at least an inch or two away from the frame while standing.

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