At what age do you switch from a 20-inch bike to a 24-inch one?
If your child has almost outgrown their current bike and you’re wondering when the right time is to move up to 24-inch wheels, you’re in the right place. The answer depends on age, height, and riding style—and in this guide, we’ll explain everything.
The quick answer
In general, children move from a 20" bike to a 24" bike between 7 and 10 years old, when they reach a height of around 135–145 cm. But age alone isn’t enough: build and leg length matter much more.
Approximate children’s bike size chart
| Age | Child’s height | Recommended wheel size |
|---|---|---|
| 3–5 years | 95–105 cm | 12" - 14" |
| 5–7 years | 105–120 cm | 16" |
| 7–10 years | 120–135 cm | 20" |
| 10–13 years | 135–145 cm | 24" |
| 13+ years | 150+ cm | 26" - 27.5" |
How can you tell if the 20" bike has become too small?
Here are the signs that it’s time for a change:
- Your child’s knees touch the handlebars while pedaling
- The seat is already at its maximum height and their legs are still too bent
- Your child feels uncomfortable or struggles to pedal smoothly
- The bike seems unstable because your child has grown too much for the frame
Why is the right size so important?
A bike that’s too small tires your child and can lead to poor posture. A bike that’s too large, on the other hand, is difficult to control and can be dangerous, especially when braking. The right size ensures safety, comfort, and enjoyment while riding.
How do you measure correctly?
The most reliable method is to measure inseam height: have your child stand upright while wearing shoes, then measure from the ankle to the groin. Multiply this measurement by 0.55 to calculate the ideal seat height in centimeters.
Alternatively, the simplest method is to have your child try the bike directly: they should be able to touch the ground with both feet (even just with their toes) and have their legs slightly bent at the bottom of the pedal stroke.
24" bike with gears or without?
For children between 7 and 9 years old who mainly ride in the city or on flat routes, a single-speed bike is easier to manage. For older children or those riding on hills and mixed terrain, a 24" MTB with gears (18 speeds) offers much greater versatility.
Come and try it at Cicli Sergio Bianchi in Florence
The best advice we can give you is to bring your child to the store and let them try the bike. At Cicli Sergio Bianchi in Florence, we’ve been helping families choose the right bike for every age and body type for four generations. Our team will guide you through the choice without rushing or pressure.
📍 Cicli Sergio Bianchi – Florence
Discover our selection of children’s bikes online, or come and visit us in store.