Kids’ bikes — Trek’s and Giant’s charts as printed

From Trek (as printed):

“Adult bikes are measured by frame size, but kids' bikes are measured by wheel diameter. Sizes range from 12" to 26".”

“Your child's age and height will help guide you to the right wheel size.”

“Once you have an idea of wheel size, consider measuring your child's inseam, too.”

“Size brackets are wide and tend to overlap, plus all bikes fit differently (even if they're the same wheel size), so head down to your local bike shop with your child for some fun test rides!”

“If your child is older than 12 and/or taller than 4' 8" you can start looking at adult bikes.”

From Giant (as printed):

“Youth bikes are often available with different wheel diameters for different heights. For example, Giant STP mountain bikes are available with 20", 24" and 26" wheel diameters to meet the needs of young riders between 110cm and 160cm tall. Choosing bike size by age is not recommended. A more precise way is to measure the inseam height and refer to our inseam height-size table to determine the correct size.”

“Ask your child to stand with his or her back to a wall, feet at shoulder width while wearing the shoes they will ride in.”

“Place a thick book between the child's legs, spine side up. Have them raise the book and hold it against the wall as if they were sitting on it like a saddle.”

“Mark the height of the book spine on the wall.”

“Use a tape measure to determine the distance between the floor and the mark on the wall. This is the inseam height.”

“Use our inseam height-size table to determine the correct size.”

“When this happens, parents often opt for the larger-sized bike so the child can "grow into it." However, as mentioned earlier, there are other factors to consider. If the child is forced to ride a bike that is too large, their comfort and control can be compromised. If you're unsure of the correct size, please visit an authorised Giant retailer for professional assistance.”

From Giant (as printed):

“The size of bike you choose should be based on the rider's inseam length, not according to their age alone, as every child is different.”

“Have your rider stand with their back and heels against the wall. Make sure their legs are straight.”

“Using their fingtertip, ask the rider to find their hipbone. Have them hold their finger on that spot. [sic]”

“Have the rider lift their knee to a 90-degree angle, while maintaining a finger on their hip joint. Slowly and repeatedly have them lift and lower their knee to confirm the location of their hip joint; this is the pivot location.”

“Once the spot is confirmed, have the rider place their finger on the pivot location, and lower their leg to the straight position.”

“Take the tape measure and measure from the middle of the rider's foot, up to their fingertip. Write this number down.”

“Use the Guide (Below) to find the right size bike for your rider!”