A 9-year-old is right at the jump from 20 to 24 inches: the average height is about 4 ft 4 in (133 cm), the cutoff between the two. If they're taller than 4 ft 4 in-4 ft 5 in (133-135 cm), get a 24"; if they're shorter, a 20" will still fit them well.
- Typical height
- 4′4″ 133 cm; range 4′0″–4′9″ (121–144 cm)
- Their bike
- 24" or 20-inch
- Bike weight
- < 18.7 lb 8.5 kg: 30% of about 62 lb (28 kg)
Calculate with their exact height
How tall is a 9-year-old?
According to the World Health Organization (WHO), half of 9-year-old boys are taller than 52.2 in (132.6 cm) and half of girls are taller than 52.2 in (132.5 cm). Between the 3rd and 97th percentiles (94% of kids) the range is wide: from 4′0″ to 4′9″ (121-144 cm). In the US, the CDC growth charts give a median of 52.6 in (133.5 cm) for boys and 52.3 in (132.9 cm) for girls. That's why age is a guide, but height is what decides the bike: measure your child barefoot against a wall before you buy.
| 3rd percentile | Median | 97th percentile | |
|---|---|---|---|
| Boys | 47.8 in (121.3 cm) | 52.2 in (132.6 cm) | 56.7 in (143.9 cm) |
| Girls | 47.6 in (121.0 cm) | 52.2 in (132.5 cm) | 56.7 in (144.0 cm) |
What size bike they need
A 24" (4 ft 2 in-4 ft 11 in / 127-150 cm) will last them until 11 or 12, so if it's time, it's a good moment to buy one. If your child is on the small side (under 4 ft 2 in / 128 cm), keep the 20" until the seatpost reaches its max mark. If they're on the tall side (over 4 ft 8 in / 142 cm), also look at 26" or 27.5" bikes in size XS, which start at about 4 ft 7 in (140 cm).
| Size | Height | Inseam |
|---|---|---|
| 20-inch | 3′9″–4′5″ (115–135 cm) | 20–24 in (50–62 cm) |
| 24-inch | 4′2″–4′11″ (127–150 cm) | 23–28 in (58–70 cm) |
How to check the fit
Leg almost straight with the pedal at the bottom and toes on the ground when seated. On a 24", check that there's clearance between the crotch and the top tube when they stand over the bike: many 24" bikes have a high frame. The brake levers should be within two-finger reach.
Ideal bike weight
At 9, a child weighs about 62 lb (28 kg); 30% is about 18.5 lb (8.5 kg). A good lightweight 24" comes in around 20 lb (9 kg) (Woom's 24" weighs 19.8 lb / 9 kg without pedals).
Brakes: coaster brake or hand brakes
Two hand brakes, and discs if possible if they'll ride trails. Kids this age already descend fast; a good rear brake and a well-adjusted front brake are what keep them safe. Teach them to use the front brake more on straight sections, and smoothly.
Gears
On a 24", 6-9 gears with a single chainring. They can now understand when to shift and use the gears well on climbs. At this age, a trigger shifter (two levers) is more precise than a twist shifter.
Training wheels or a balance bike
No training wheels at all. What helps now is practicing skills and riding safely in traffic: hand signals, looking back, yielding at crosswalks. Many cycling clubs and community programs run classes for kids this age.
What to look for when you buy
- Size: 24" if they're taller than 4 ft 4 in-4 ft 5 in (133-135 cm); 20" if shorter.
- Weight: under 22 lb (10 kg) for a 24".
- Disc brakes if they ride trails.
- Short cranks to match their legs: adult cranks are far too long.
- If they're very tall, look at XS 26" or 27.5" bikes.
Frequently asked questions
What size bike for a 9-year-old?
24 inches if they're taller than about 4 ft 4 in (133 cm); if they're shorter, 20 inches.
What height is a 24-inch bike for?
For kids from about 4 ft 2 in to 4 ft 11 in (127-150 cm) tall, usually ages 8 to 12.
How much should a 24-inch bike weigh?
Ideally no more than 20-22 lb (9-10 kg). For a 62 lb (28 kg) child, 30% is 18.5 lb (8.5 kg).
Sources
- WHO: Height-for-age, boys 2 to 5 years (percentiles)
- WHO: Height-for-age, girls 2 to 5 years (percentiles)
- WHO: Height-for-age, boys 5 to 19 years (percentiles)
- WHO: Height-for-age, girls 5 to 19 years (percentiles)
- CDC: Growth charts data tables, stature-for-age, 2 to 20 years
- Woom: Compare woom bikes
- Islabikes: Size chart
- Trek: Precaliber kids’ bikes
- Decathlon: Btwin Original 100 20" manual
- Mercê C et al. (2022). Learning to Cycle: From Training Wheels to Balance Bike. IJERPH
- Two Wheeling Tots: Kids’ bike buying guide