How do you measure a child for a bike?

measuring child for kids bike

How do you size a child for a bike? What size bike do I need for my child? How to choose the right bike size? Let's start by measuring them correctly...


Measuring your child and getting the correct size of bike for them can be tricky. Some people use wheel size, age or inside leg measurement to work it out, but we find that your child’s height is the best way to calculate what bike will fit them correctly.

Why height?


Height is the most universally understood measurement. It’s simple. You get your child to stand against a wall, put a book or similar on their head at ninety degrees to the wall and mark it off. Then measure from the ground to the mark and you have their height. Dead easy, and a very accurate method. We tell people to make the measurement with their child wearing shoes, because no one rides a bike barefooted… do they!?

This measurement then allows you to match a bike to your child’s height. Our design team have access to lot's of ergonomic and anthropometric data for children's sizing and many key dimensions such as leg and arm length can be calculated by knowing the child's age and height. This has all been taken into account when designing and sizing our bikes - so of you get the right bike for your child's height, the key dimensions for reach, wheelbase and standover etc will all be right. Each bike can then be individually 'tweaked' for the child, by adjusting bar height and moving the saddle back or forward (and or course up and down). Then with our PINTO and SKØG bikes the frames and gearing grow proportionally as the child grows.

Age and height can vary wildly


If there is one thing that we have learned it is that age and height can often be totally unrelated. You can have a really tall three year old and a really short six year old that fit on the same bike. Even twins can vary hugely in size and height. There are so many factors that can effect this, from gender, genetics, environment, etc. Basically age is a really bad way to calculate what size of bike (or clothes, or shoes, etc.) your child will need. Of course there are charts with average height and ages on (it’s all percentage percentiles and stuff like that), but in the real world these are often useless.

If there is such thing as an ‘average’ height you also have to factor in the different ways that boys and girls grow and develop, especially as they get older. You’ll often see quite tall pre-teenage girls dwarfing their male classmates or friends. Fast forward five or six years and the boys tend to overtake them. So growth patterns are complicated things.

Why not inside leg?


Measuring your child’s inside leg is seen by many as the best way to ‘size’ a child for a bike. In our experience it is problematic. Why? Because it’s hard to get right. The idea is to get your child to stand against against a wall, then carefully put a book between their legs up to their crotch. You then get them to step away, mark the top of the book and then measure the distance from the mark to the floor.

We tested this method on numerous friends and members of our families with their children and the variation in measurements was shockingly funny! Often the same child would come out with two totally different measurements depending on who was attempting to measure them (even between mums and dads of the same child!).

Sometimes this was down to a wriggling child, but more often than not it was baggy or low–slung trousers. The low-slung trousers aren’t a fashion statement, it is just the nature of young children’s clothes. They tend to hang low, proportionately they have lots of stitching in the crotch for the area it covers, which often gets in the way when measuring.

This real world testing that we did clearly told us that the inside leg measurement is not the easiest thing to get, not with any real accuracy any way. It seems simple enough to do, but in reality it is not the case.

Standover


The only time that we do think that the inside leg measurement is vitally important is when you need to double-check the standover height of the bike (the distance from the floor to the top of the top-tube). This is an important measurement because it lets you know if your child can stand over the bike with their feet on the ground. Our bikes are designed with this 'pre-calculated' based on the rider's height, but if your child is very close to the minimum height for a bike, inside leg can then be a really helpful deciding factor - but it must be taken really accurately.

Proportions


We all know that as children grow they go through a lot of changes. We sometimes think that children’s bodies change proportionately, but growth affects different parts of their bodies at different rates. A child grows the most in its first 12 months of its life, and after that it slows down until around 16–18 years of age when it stops altogether. Oddly a child’s head reaches almost full size by the age of one, that is why babies and toddlers often seem top heavy.

By the age of three most children become slimmer, losing their ‘puppy fat’ and rounded tummy. Their rate of leg and arm growth varies also by age, then as they grow and mature there are many external factors that can affect their size. There's a lot to consider, but we've taken this all into account in the design of our bikes. From our extensive research and data-driven design, followed by tonnes of real-world testing, using riders of all ages, shapes and sizes.