Quick answer: As a rough guide, the K4 is the starter bike for first-timers from about three, the K7 Pro suits six to ten, the K10 Pro eight to fourteen and the K22 fourteen and over. But age only gets you to roughly the right bike — height is what decides it. Our Does It Fit tool takes twenty seconds, asks three questions and draws your child to scale next to the bike, and it is the single best thing you can do before ordering.
Age gets you close. Height gets you right.
Two eight-year-olds can be twenty centimetres apart. One of them is ready for a bigger bike and one of them isn't, and their birthday tells you nothing about which is which.
So use the age bands below to narrow it down to one or two bikes, then check the fit properly. Every section here ends with the same advice for that reason.
Not sure of the size? It's the question we get asked more than any other. Does It Fit answers it in three questions — age, height and how confident a rider they are — and shows your child drawn next to the bike so you can see it rather than guess it. Check the fit →
The question nobody asks until January
There's a second question hiding behind "which bike for a six-year-old", and it's the one that actually matters at Christmas.
Will it still fit them next Christmas?
Children grow roughly five or six centimetres a year. Buy a bike your child is already near the top of, and you'll have a brilliant Christmas and a frustrated child by the summer. Buy one they're at the bottom of and they can't get their feet down, which is worse — a bike that's too big is frightening, and a frightened child doesn't ride.
The sweet spot is the lower-middle of a bike's height range. That's where they can ride confidently now and still have years in it.
Each age band below says how much room you're buying.
Ages 3 to 5 — the Kubbi K4
This is the first-bike band, and the K4 is the only Kubbi that fits it.
A typical three-year-old sits near the bottom of the K4's 80–115cm range, which is exactly where you want them. Realistically you're buying about two years of riding before they're ready to move up — the K4 is a starter bike and it's meant to be outgrown.
By five, most children are moving on. Plenty are already around 110cm, close to the K4's ceiling, so you're buying one good year rather than two. If your five-year-old is average height or taller and has ridden something before, look at the next band instead.
Will it still fit next Christmas? For a three or four-year-old, yes. For a five-year-old, probably not for long after that.
If they're at the very young end, read Electric Bike for Toddlers: Is Your Child Ready? before you buy. Three is genuinely possible, but readiness isn't only about height.
Check the fit: Does It Fit
Ages 6 to 7 — K4 or K7 Pro
This is the band people get wrong most often, because both bikes are defensible and the right answer depends entirely on the child.
The K4 if they've never ridden anything with a throttle, or they're small for their age. Lighter, lower, less bike — and confidence matters more at six than power does.
The K7 Pro if they're average height or taller, or they've already ridden. Three speed settings instead of two, so there's somewhere to progress to, and its 100–145cm range means a six-year-old has four or five years in it.
The honest tiebreak: by six, most children are at or near the top of the K4. If they can ride a K7 Pro safely now, it's the better Christmas present — you'd otherwise be replacing the K4 within a year or so.
Will it still fit next Christmas? K4, only if they're small for their age. K7 Pro, easily.
Check the fit: Does It Fit — this band in particular, because "six" on its own genuinely doesn't answer it.
Ages 8 to 10 — K7 Pro or K10 Pro
The step up to a bike that feels serious.
The K7 Pro is still right for an eight or nine-year-old of average height, especially a first-time rider. Its range runs to 145cm, so most children have a couple of years left in it.
The K10 Pro is for a confident rider, or a tall one. 800W, three speed settings, dual suspension and a 90kg rider limit — which is the number that matters here. A ten-year-old on a K10 Pro is not going to outgrow it before they're a teenager.
If they've already had a smaller bike and they're asking for something faster, this is that present. There's a fuller guide at The Best Electric Scrambler for Kids.
Will it still fit next Christmas? Both yes. The K10 Pro will still fit in four.
Check the fit: Does It Fit
Ages 11 to 13 — the K10 Pro
For most children in this band the K10 Pro is the bike. Its 120–155cm range covers the great majority of eleven to thirteen-year-olds, and the 90kg rider limit means it's the last bike a lot of families buy before an adult-sized one.
The exception is a tall thirteen-year-old. If they're already over about 155cm, they've run out of K10 Pro before they've started, and the K22 is the honest answer even though the age band says otherwise. This is exactly the case where measuring beats the box.
Will it still fit next Christmas? For an eleven or twelve-year-old, yes. For a thirteen-year-old mid-growth-spurt, measure first.
Check the fit: Does It Fit
Ages 14 and over — the K22
A full-size machine. 2000W, hydraulic brakes, around 50km of range, and 55km/h at the top setting — with parental speed controls still there, so you decide what they can actually reach.
The K22 fits riders from 128cm to 179cm and takes a 100kg rider, which means it isn't outgrown — it's the bike they keep. For a teenager who's been riding for years, this is the present that lands.
Will it still fit next Christmas? And the one after that, and probably the one after that.
Check the fit: Does It Fit
How much room you're buying
| Bike | Rider height | Seat height | Max rider | Age at bottom of range | Years of room |
|---|---|---|---|---|---|
| K4 | 80–115cm | 45cm | 40kg | 3 | About 2 — a starter bike |
| K7 Pro | 100–145cm | 58cm | 60kg | 5–6 | 4–5 |
| K10 Pro | 120–155cm | 67cm | 90kg | 8 | 4–5 |
| K22 | 128–179cm | 78cm | 100kg | 12–14 | 5+ |
Heights are a guide — children vary enormously at the same age. Run the real numbers through Does It Fit rather than working from the table.
Buying for a child you don't see every week
Grandparents, aunts, uncles, godparents — this one's for you.
Buying a bike for a child whose current height you're guessing at is the hardest version of this problem, and it's very common at Christmas.
The best option is to ask. A parent can measure a child in ten seconds, and "how tall is she at the minute?" is a much less suspicious question than it feels.
If you can't ask, go by what you know. A child you last saw in the summer has grown since. Err towards the bike with the most room above them rather than the one that fits perfectly today — as long as they can still get their feet down.
If you're genuinely stuck between two, get in touch before you order rather than after. Sizing is the thing we're asked about most and we'd far rather have the conversation in November.
Check the fit: Does It Fit
Frequently asked questions
What age can a child start riding an electric dirt bike?
From around three, if they're tall enough to get their feet down on the K4. Height and confidence matter more than the birthday — there's a full breakdown in our UK age and size guide.
My child is between two sizes. Which do I get?
Usually the smaller one, if they're a first-time rider — confidence comes before power. The bigger one if they've ridden before and can get their feet down on it. Does It Fit will tell you which side of the line they're on, and if it's genuinely borderline, ask us.
How do I measure my child properly?
Height against a wall in the shoes they'd ride in, and inside leg from the floor to the top of the inner thigh. The inside leg is the one that matters, because it decides whether they can get their feet down on the seat.
Will they outgrow it in a year?
Not if you buy at the lower-middle of a bike's height range. The K4 is the exception and it's deliberate — it's a starter bike, and most children move up from it around five or six. From the K7 Pro upwards you're looking at three or four years a bike. The table above shows how much room each one gives you.
Is a bike too big a present for a young child?
For a three or four-year-old it's usually the main gift rather than one of several. If you're weighing that up, our Christmas gift guide goes through it, and Screen-Free Christmas Gifts That Actually Get Used makes the case for why a bike keeps being used when other presents don't.
What if I get the size wrong?
Talk to us before you order and you probably won't. If it does arrive and it's clearly the wrong size, get in touch — see our returns policy.
The bottom line
Age narrows it to one or two bikes. Height picks between them. And the question worth asking before you order is not just "does this fit now" but "will it still fit next Christmas" — because the bike that fits perfectly on Christmas morning is often the one that's too small by the summer.
Twenty seconds on Does It Fit will settle it.