Generally, a 20 inch bike can refer to both a wheel bike or a frame bike.

The wheel size is how the kids’ bikes are measured and sized, whereas the frame size is how the adult bikes are sized along with the wheel size.

So, if you are looking at how big of a size the bike can be for your kid, then you need to look at the size of the wheels.

However, just knowing the size of the wheels alone is not sufficient to get a grasp on how big the bicycle is going to be.

Below we touch upon all the aspects that you need to consider when trying to figure out how big a 20 inch bike is.

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How Big Is A 20 Inch Wheel Bike:

A 20 inch bike is a size that straddles an 18 inch bike on the lower end and a 24 inch bike on the top end.

A 20 inch wheel bike for kids has a wheel diameter of 20 inches, i.e., the wheels measure 20 inches across.

Its an ideal bike size for 6 year old and 7 year old kids.

But mentioning the wheel size alone would not give an adequate picture of how big the bike can be.

There are two specifications of the bike that you need to keep in mind when looking at how big the bike is in addition to the wheel size – the standover height and reach.

Standover Height: This is the height of the bike from the floor to a specific point on the top tube (top tube is the tube that connects the seat post to the handlebars) where the rider typically is at when standing over the bike when the bike is stationary.

The standover height can vary for the same wheel size depending on the type of the bike (mountain, BMX, road, cruiser, etc.) as well as for different brands and models.

Optimal standover height imparts confidence to the rider especially if they are during the learning phase or starting out with biking.

This would roughly be around 49 cm for a 20 inch bike.

Frame Reach And Stack: Roughly, this denotes how much space is there for the rider between the saddle, cranks, and handlebars.

To put it technically, this is roughly the measurement of the area between the bottom bracket (the part where cranks are fitted), the top tube, and the head tube (the part that connects the fork to the handlebars).

This also helps to position the rider properly on the saddle without having to overextend to the front of the bike by sitting way back on the saddle or having less-than-optimal space where the rider can feel cramped.

Optimal space is required for the rider to feel comfortable and at ease with the bike.

Adequate space helps with efficient pedaling and control of the bike too.

How Big Is A 20 Inch Bike Frame:

The frame sizing is a bit more complicated than the wheel sizing which is standard.

This is because different types of bikes (mountain, BMX, cruisers, road, etc.) are sized differently for the same frame size.

The adult’s bikes are sized anywhere between XX-Small to XX-Large.

For eg., a 20 inch frame on a mountain bike would be considered as a size Medium, whereas, on a road bike it would be categorized as a size Small.

The best way to get a good picture of this is by visiting the brand’s website and look at the different types and models and determine it for yourself.

The below frame size chart gives you a good idea of frame sizes for different types of bikes.

Frame Size (Mountain & Hybrid Bikes)

Frame Size

Frame Size (inches)

Frame Size Centimeters

X-Small (XS)

13″ – 14″

33 – 36

Small (S)

15″ – 16″

38 – 41

Medium (M)

17″ – 18″

43 – 46

Large (L)

19″ – 20″

48 – 51

X-Large (XL)

21″ – 22″

53 – 56

XX-Large (XXL)

23″ – 24″

58 – 61

Frame Size (Road Bike)

Frame Size

Frame Size (inches)

Centimeters

XX-Small (XXS)

~18.8″

47 – 48cm

X-Small (XS)

~19.6″

49 – 50cm

Small (S)

~20.8″

51 – 53cm

Medium (M)

~21.6″

54 – 55cm

Large (L)

~22.8″

56 – 58cm

X-Large (XL)

~23.6″

58 – 60cm

XX-Large (XXL)

~24.8″

61 – 63cm

How Big Is A 20 Inch BMX Bike:

BMX bikes are sized based on the wheel size as well as the top tube length – meaning you need to consider both these aspects before deciding on one.

Normally, when the inch size is mentioned for a BMX bike, it would denote the size of the wheels. So, a 20 inch BMX bike will have 20 inch wheels.

The 20 inch wheels are the measurement of the diameter of the wheels.

But, you also need to take into account the top tube length too depending on the age and height of the rider.

The top tube length for a 20 inch BMX bike can vary between 18 inches to 21 inches.

How Big Is A 20 Inch Mountain Bike:

A 20 inch mountain bike can refer to a kid’s bike or an adult bike depending on what the 20 inch entails.

A 20 inch kids mountain bike refers to the size of the wheels and is generally for kids between 6 and 7 years of age.

A 20 inch frame mountain bike however refers to the size of the frame and is categorized as a size Medium bike and is good for riders between 5’6” and 5’10” tall.

How Big Is A 20 Inch Bike In cm:

A 20 inch bike frame is sized Large for mountain and hybrid bikes and measures 50-52 centimeters.

For a road bike, a 20 inch frame would be sized Small and would be roughly 51-53 cm in length.

What Size Is A 20 Inch Bike:

The sizing of a 20 inch bike varies depending on the type of bike.

For example, road bikes require a different geometry compared to that of a mountain bike or BMX bike.

A road racing bike is more tailored for aerodynamics, whereas a mountain bike’s geometry is for good control of the bike that is required while maneuvering the obstacles on a trail.

A hybrid bike on the other hand will have geometry somewhere between that of a road and a mountain bike.

The below sizing is what is generally followed for 20 inch bike frames:

  • Mountain – Medium
  • Road – Small
  • Hybrid – Large

What Size Is A 20 Inch Mountain Bike Frame?

A 20 inch mountain bike frame is size Medium and is between 17 and 18 inches in length.

This size straddles a size Small on the lower end and a size Large on the top end.

Is A 20 Inch Bike Small?

A 20 inch frame bike is sized Small for a road bike; Medium for a mountain bike as well as for a Hybrid bike.

Check the below posts for additional information:

20 inch bikes

18 inch bikes

24 inch bikes

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