What Size Dirt Bike Does My Kid Need?
It's the first question every parent asks, and the honest answer is: it depends more on your kid than the number on the engine. Here's how to actually work it out.
Start with the ground, not the age chart
Age-based sizing charts are a rough guide at best. What actually matters is whether your rider can sit on the bike and touch the ground with the balls of their feet, so they can steady themselves at a stop without panicking. If they're flat-footed and still have bent knees, the bike's probably too small for long; if they're up on their toes stretching, it's too big.
A rough 50cc–125cc ladder
- 50cc — genuine first-timers, usually 4 to 7 years old, often automatic or single-speed so there's no clutch to learn alongside balance.
- 65cc — the step up once a 50 feels too slow, usually geared riders around 7 to 10.
- 85cc — a real junior motocross bike with genuine power. Best for young riders who've already got some seat time, not absolute beginners.
- 110cc–125cc — bigger or more experienced young riders, often the last step before a full-size bike.
These bands overlap a lot in practice. A tall, confident 8-year-old might be ready for an 85 while a smaller or more cautious 10-year-old might still be happiest on a 65.
Reach the controls, not just the ground
Sizing isn't only about leg length. Your rider also needs to comfortably reach the handlebars, work the clutch and brake levers, and see over the bars without craning their neck. If they're hunched or stretching to reach anything, it's affecting their control, not just their comfort.
Don't buy to "grow into"
It's tempting to size up so the bike lasts longer, but a bike that's too powerful or too tall can knock a young rider's confidence hard, sometimes permanently. Kids grow fast, and dirt bikes hold their value well — it's almost always better to buy the right size now and sell it on when they outgrow it than to start them on something that scares them off riding altogether.
What we have, and what happens when they outgrow it
We carry kids' and junior bikes most weeks, including the KTM 85 SX and Kawasaki KX85 — see our kids' dirt bikes page for what's in stock right now. Every bike goes through our own workshop before it's listed. When your rider's ready for the next size, we buy bikes back too — see Sell Us Your Bike for a sale value you can put straight towards the upgrade.
Frequently asked questions
What size dirt bike is right for a 6-year-old?
Most 6-year-olds starting out do well on a 50cc bike, but it really comes down to their height and confidence rather than age alone. They should be able to touch the ground with the balls of their feet.
Is an 85cc dirt bike too big for a beginner?
For a complete first-timer, usually yes — an 85cc junior motocross bike has real power and suits young riders who already have some experience on a smaller bike.
Should I buy a bigger bike so my child grows into it?
We'd generally say no. A bike that's too big or powerful can be intimidating and knock a young rider's confidence. It's better to buy the right size now and trade up as they grow.
Do you help with sizing in person?
Yes — tell us your rider's height, weight and experience and we'll point you at bikes in stock that suit, or let you know what to look for.