16 vs 20 Inch Kids Bike: Which Size by Age & Height?
Quick answer: A 16 inch kids bike suits most children aged about 4–6 (roughly 105–120 cm tall), while a 20 inch kids bike suits confident riders aged about 6–9 (roughly 120–140 cm). The overlap sits around age 6, so when your child is between sizes, measure their inside leg (inseam) and let that decide. As a rule, a 16" works for inside legs of about 45–55 cm and a 20" for about 60–74 cm. Not sure? Confirm the fit in seconds with our free Kids Bike Size Calculator.
16 inch vs 20 inch: quick answer
Choosing between a 16 inch and a 20 inch bike is the most common sizing decision Australian parents face, because it covers the years when kids move from training wheels to confident, geared riding. The short version: pick the 16" if your child is younger or still building balance, and the 20" if they are taller, more confident, and ready for gears and hand brakes.
The two sizes overlap right around age 6 and roughly 120 cm, which is exactly why age on its own is a weak guide. A small, cautious six year old is usually happier finishing off on a 16", while a tall, confident six year old will often be cramped on one and ride far better on a 20". The deciding factor is almost always inside leg length, not the number of candles on the birthday cake.
Here is the simplest way to think about it:
- Choose a 16 inch bike if your child is about 4–6, around 105–120 cm, with an inside leg of roughly 45–55 cm, and still gaining confidence (often with training wheels).
- Choose a 20 inch bike if your child is about 6–9, around 120–140 cm, with an inside leg of roughly 60–74 cm, can ride unassisted, and is ready for gears and hand brakes.
- Right on the line? If the inside leg falls in the 55–60 cm gap, weigh up confidence and leg length. Size down for an anxious rider; size up for a bold one with long legs.
16 inch vs 20 inch kids bike size by age and height
Use the chart below as your starting point. We have included the neighbouring sizes (14", 18" and 24") so you can see where the 16" and 20" sit in the wider range and rule them in or out at a glance. Wheel size is the label kids' bikes are sold by, so it is the quickest way to narrow your search before you check the finer fit details.
| Wheel size | Typical age | Child height | Inside leg (inseam) | Best for |
|---|---|---|---|---|
| 14" | 3–5 years | 95–110 cm | 40–50 cm | First pedal bike after a balance bike |
| 16" | 4–6 years | 105–120 cm | 45–55 cm | Learning to pedal, building confidence (training wheels) |
| 18" | 5–7 years | 115–128 cm | 55–63 cm | In-between size; less common in Australia |
| 20" | 6–9 years | 120–140 cm | 60–74 cm | Confident riding with gears & hand brakes |
| 24" | 8–11 years | 135–155 cm | 72–86 cm | Pre-teen riders ready for an adult-style bike |
These ranges are a guide. Children of the same age can vary by a full wheel size, so height and especially inside leg give a far more reliable fit than age alone. When your child sits between two sizes, size down for confidence and size up only when the legs and skill clearly support it.
What size bike for a 6, 7 or 8 year old?
This age band is exactly where the 16"/20" decision lives, so it is worth spelling out:
- What size bike for a 6 year old? Age 6 is the crossover point. A smaller or less confident six year old often suits a 16", while a taller, capable six year old is usually ready for a 20". Measure the inside leg to break the tie.
- What size bike for a 7 year old? Most seven year olds are comfortable on a 20 inch bike. Only smaller children with a shorter inside leg will still want a 16".
- What size bike for an 8 year old? A 20" suits the majority of eight year olds. Taller pre-teens may be approaching a 24", so check the inside leg against the chart above.
How to measure inside leg & when to size up
The single best predictor of the right bike is your child's inside leg (also called inseam). It tells you whether they can stand over the frame and stop safely, which matters far more than matching an age range.
To measure it at home:
- Have your child stand barefoot with their back against a wall, feet about shoulder-width apart.
- Pop a hardcover book between their legs, spine upward, and slide it up gently until it sits where a saddle would.
- Keep the book level and measure from the top of the spine straight down to the floor in centimetres.
That number is your child's inside leg. Match it to the table above: about 45–55 cm points to a 16", and about 60–74 cm points to a 20".
When to size up from a 16" to a 20"
It is time to move up to a 20 inch bike when you notice the tell-tale signs that a 16" has been outgrown:
- The saddle is already near the top of its adjustment range and the knees still rise high while pedalling.
- Your child looks cramped — elbows tucked in, body hunched over the bars.
- They ride confidently and unassisted, brake well, and want to go faster or further than the little bike allows.
- Their inside leg measures around 60 cm or more.
Don't size up too early. Buying a 20" "to grow into" before your child is ready usually backfires — an oversized bike is harder to start, stop and steer, so kids ride it less. A correctly fitted bike that gets used every week beats a big one that sits in the garage.
Gears, brakes & weight — what else matters at 20"
Moving from a 16" to a 20" is not just about bigger wheels. The 20" size is where bikes usually grow up, and a few features change the riding experience:
Gears
Most 16" bikes are single-speed, while many 20" bikes add gears. Gears let kids tackle hills and longer rides without exhausting their legs — a big step up in capability for confident riders.
Brakes
16" bikes often rely on a coaster (back-pedal) brake plus a hand brake. By 20", hand brakes — ideally disc brakes — do the work, so check your child's hands can reach and squeeze the levers comfortably.
Weight
A lighter bike is easier for a child to control, lift and pedal. Magnesium-alloy frames keep 20" bikes light, which makes the bigger wheel size far less intimidating for younger riders.
Standover & reach
Whichever size you choose, your child should clear the top tube with both feet flat and reach the bars with a slight bend in the elbows. Good standover clearance keeps stops calm and confident.
If your child is ready for the next step, our 20" Gear Force kids bike ticks these boxes with a lightweight magnesium-alloy frame, Shimano gears and disc brakes. You can also compare the full range of kids bikes by size to find the right fit.
Still unsure? Use the calculator
If your child sits right on the line, or you would rather double-check before buying, our interactive tool does the matching for you. Enter your child's age, height, or — best of all — their inside leg, and it returns the recommended wheel size and the closest Gear Force bike in seconds.
Open the free Kids Bike Size Calculator →
For more sizing help, safety tips and buying advice, browse the full Guides hub. And if your little one is not quite ready for a pedal bike yet, start with the right first ride: see our picks for the best toddler trikes in Australia or the best balance bikes in Australia to build balance first.
FAQ: 16 inch vs 20 inch kids bikes
What size bike for a 6, 7 or 8 year old?
A 6 year old is at the crossover — smaller or less confident kids suit a 16", taller or bolder ones a 20". Most 7 and 8 year olds fit a 20 inch bike, with only smaller seven year olds still on a 16". Always confirm with the inside-leg measurement: roughly 45–55 cm for a 16" and 60–74 cm for a 20".
Can a 5 year old ride a 20 inch bike?
Usually not comfortably. A 20" is built for an inside leg of about 60 cm or more, which most five year olds have not reached. Putting a 5 year old on a 20" tends to mean tiptoe stops, nervous starts and poor control. A 16" (or even a 14") is almost always the safer, more confidence-building choice at that age. If your five year old is unusually tall, measure the inside leg and check it against the chart before deciding.
16 or 20 inch — how do I decide when my child is between sizes?
Measure the inside leg first. If it falls in the 55–60 cm gap, weigh up confidence and leg length: size down to a 16" for a cautious rider who values easy stops, or size up to a 20" for a confident child with long legs who is ready for gears. When in doubt, sizing down protects confidence — you can always move up next season. Our Kids Bike Size Calculator makes the call for you in seconds.
Is a 20 inch bike harder for a child to ride than a 16"?
Only if it does not fit. For a child with the right inside leg, a well-fitted 20" actually rides better than an outgrown 16" — it is more stable at speed and easier to pedal. The extra features (gears and hand brakes) add capability without making it harder, provided your child can reach the brake levers and the bike is light enough to handle. A lightweight magnesium-alloy frame makes a big difference here.
The bottom line
Pick a 16 inch bike for a younger or still-learning child (about 4–6, 105–120 cm, inside leg 45–55 cm) and a 20 inch bike for a confident rider ready for gears and hand brakes (about 6–9, 120–140 cm, inside leg 60–74 cm). Around age 6 the two overlap, so let the inside-leg measurement — not age — make the final call, and size down rather than up whenever you are unsure.
When your child is ready to move up, the Gear Force 20" kids bike gives them a light magnesium frame, gears and disc brakes to grow with. Browse the full kids bikes range, and if you would like the fit confirmed before you buy, run the numbers through our free Kids Bike Size Calculator.
At Gear Force, we’re all about helping Aussie families create fun, functional, and inspiring spaces — from playtime adventures to everyday living. We started with ride-on toys, bikes, and gear for kids, and we’re continuing to grow into new categories that bring joy, comfort, and practicality to family life.
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