An 8-year-old needs a 20-inch bike if they're shorter than about 4 ft 4 in (133 cm), and a 24" if they're taller. The average height at this age is about 4 ft 2 in (127 cm), so most are still on a 20".
- Typical height
- 4′2″ 127 cm; range 3′10″–4′6″ (116–138 cm)
- Their bike
- 20" or 24-inch
- Bike weight
- < 16.5 lb 7.5 kg: 30% of about 55 lb (25 kg)
Calculate with their exact height
How tall is a 8-year-old?
According to the World Health Organization (WHO), half of 8-year-old boys are taller than 50.1 in (127.3 cm) and half of girls are taller than 49.8 in (126.6 cm). Between the 3rd and 97th percentiles (94% of kids) the range is wide: from 3′10″ to 4′6″ (116-138 cm). In the US, the CDC growth charts give a median of 50.4 in (127.9 cm) for boys and 50.2 in (127.6 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 | 45.9 in (116.6 cm) | 50.1 in (127.3 cm) | 54.3 in (137.9 cm) |
| Girls | 45.6 in (115.7 cm) | 49.8 in (126.6 cm) | 54.1 in (137.5 cm) |
What size bike they need
24" bikes start at 4 ft 1 in-4 ft 5 in (125-135 cm) depending on the brand (Woom from 125 cm, Islabikes from 127 cm, Trek from 130 cm, Decathlon from 135 cm). If your child is 4 ft 3 in-4 ft 5 in (130-135 cm), they're in the zone where both work: the 20" will feel quicker and lighter, and the 24" will last until 11 or 12. Let the inseam decide: they need to reach the ground with their toes with the 24" bike's seat all the way down.
| 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. If they ride a 20" and the seatpost is pulled out nearly to the minimum insertion mark, they'll need a 24" soon. Check the handlebar too: if their knees hit it when turning, they've outgrown the bike.
Ideal bike weight
At 8, a child weighs about 55 lb (25 kg). 30% is 16.5 lb (7.5 kg): a good 20" comes close (Woom's 20" weighs 17.2 lb / 7.8 kg without pedals), but few 24" bikes get under 20 lb (9 kg). That's another reason not to jump to a 24" early if their height doesn't call for it.
Brakes: coaster brake or hand brakes
Two hand brakes, no exceptions. At this age they start going faster and riding in more places: disc brakes (hydraulic on higher-end models) give them more control on descents and in the rain. Check that the pads aren't worn: kids brake a lot, and hard.
Gears
Gears start to be really useful: 6-8 speeds with a single chainring are enough to climb hills without getting off. Teach them to shift before the hill, not halfway up, and not to cross-chain. Decathlon's 24" bikes (Btwin Original 500) have 6 gears; Woom's 24" bikes, 8.
Training wheels or a balance bike
Training wheels no longer make sense. If your child still can't ride at 8, that's fine: on a bike that fits, with the pedals off at first and in a quiet area, they'll learn fast. What's worth doing at this age is practicing skills: emergency stops, swerving, looking back without drifting.
What to look for when you buy
- Under 4 ft 3 in (130 cm), 20"; over 4 ft 5 in (135 cm), 24"; in between, the inseam decides.
- Weight: a 20" under 17.5 lb (8 kg) or a 24" under 22 lb (10 kg).
- Disc brakes if they'll ride trails or in the rain.
- One chainring and 6-8 cogs.
- Short cranks to match their legs (good brands size them to the bike).
Frequently asked questions
20 or 24 inch bike for an 8-year-old?
20" if they're shorter than 4 ft 3 in-4 ft 4 in (130-133 cm); 24" if they're taller than 4 ft 5 in (135 cm). In between, it comes down to whether they can touch the ground with their toes on the 24".
How tall is an 8-year-old?
The WHO median is about 4 ft 2 in (127 cm), with 3 ft 10 in to 4 ft 6 in (116-138 cm) between the 3rd and 97th percentiles. The CDC growth charts put the US median at about 4 ft 2 in (128 cm).
Does a bike for an 8-year-old need gears?
They help a lot if there are hills. 6-8 speeds with a single chainring are plenty.
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