Length Measurement
What Is Length Measurement?
Before buying a refrigerator, you need to know how much space you have in your kitchen, otherwise you might end up with one that doesn’t fit.
The oldest way to measure something is to place two objects side by side and compare them directly. In our case, that would mean bringing the refrigerator into the kitchen to check if it fits — clearly not the most practical option.
Luckily, there are easier ways. If you don’t have a measuring tape at hand, you can always improvise. Take a piece of string, mark the height of the fridge, and bring only the string with you. It’s much lighter than the fridge itself.
You could also use your hand. Spread your thumb and index finger apart and “walk” your hand down the fridge, counting how many hand spans tall it is. That’s how the first units of measurement appeared — feet (the length of a foot), inches (the width of a thumb), and so on.
But what if you’re already at the store and still not sure the fridge will fit? Asking your kid to measure the kitchen space with her hands won’t help — her hands are smaller than yours. But if you both use the same matchbox, one at home and one in your pocket, you can measure the two spaces in matchboxes and compare the results.
Of course, we don’t actually use matchboxes for measuring. Today we rely on standard units like centimeters, meters, inches, and feet. Measuring tapes may look a little different from country to country, but within each system they work the same way. That’s what makes it possible for people anywhere in the world to describe the size of a door, a table, or even a refrigerator using just a number.
Why Does It Matter for Kids?
The famous Swiss psychologist Jean Piaget showed in his classic studies that comparing objects by length isn’t as simple for young kids as it seems. Kids aged four to six can correctly compare two sticks when they’re placed side by side, but they often get confused when one stick is moved forward or backward. A kid might say, “This one is longer now because it sticks out more.” When measuring, kids sometimes leave gaps between the matchsticks they use or, on the contrary, overlap them. Even the idea that a piece of string stays the same length when you bend or straighten it takes time to develop. A kid may insist, “It’s longer when it’s straight and shorter when it’s bent.”
Modern research confirms that learning to measure in early childhood (understanding units, scales, starting points, and estimation) strengthens both spatial and numerical reasoning. Longitudinal studies show that the pace of spatial development between ages four and six strongly predicts success in math during elementary school and even into the teenage years.
Observations also highlight how important it is to use the right tools when introducing measurement. Early on, kids should work with rulers that clearly start at zero, show only whole-number marks, and don’t skip divisions. It’s equally important for teachers to talk with kids about why all the marks on a ruler are evenly spaced and why measurements start at zero rather than one.
How Do We Teach?
Even before they start school, kids naturally compare the sizes of things around them. They try to fit a large pot into a smaller one, check if a stick can stretch across a doorway, or look for two ribbons that are the same length for their braids. Words like bigger and smaller, taller, narrower, and the same length appear early in their speech.
We build on this natural curiosity by giving kids tasks that involve comparing and ordering objects in pictures or in real life.
Next comes the idea of units — a personal “measuring tool.” Kids might line up toy cubes along a caterpillar or stack boxes beside a washing machine. Later, we introduce standard tools such as rulers marked with familiar units like centimeters or inches.
We also explore how one unit can be expressed in terms of another through simple examples with small numbers. A kid might reason, “If the fridge is as tall as three stools, and each stool is as tall as two boxes, then the fridge is as tall as six boxes.”
Another key skill is estimation. Kids learn to judge length by eye: How many cubes might fit along this string — four, twenty, or sixty? These exercises strengthen spatial sense and help kids think about numbers as flexible, meaningful quantities, not just symbols on a page.
First Steps
Comparing Objects by Length
Young kids love playing in the kitchen, lining up pots and pans by size. Trying to fit a big pot into a smaller one, or the other way around, helps them explore the idea of comparing by size in the most natural way.
As they grow, kids start to compare objects by placing them end to end. For example, they might lay out two strings of sausages one below the other to see which is longer and by how many sausages it differs.
Comparing lengths
How many more?
Step by step, their language becomes more precise. They start using words like taller and shorter, wider and narrower, longer and shorter, and later the tallest or the narrowest. They line up pencils by height — and sometimes even line themselves up that way too.
Kids also learn to compare ribbons or strings just by looking. At first, they might think that if the ends of two ribbons line up, the lengths must be equal. Gradually, they discover what happens when you stretch one ribbon out a little farther and how that connects to the idea of length.
Order by length and height
Order by height
Measuring length
Order by size
Comparing lengths
Longer and shorter
Measurements
Comparing lengths
Deep Understanding
Measurement Units
At first, it’s easiest for kids to think of a unit of length as something real and touchable that can be lined up next to an object. For example, they might measure a caterpillar with toy cubes, placing them carefully from head to tail.
Measurements
Units of measurement
If there are enough identical boxes, kids can use them to measure the height of a washing machine, a lamp, or a refrigerator. They soon notice that all boxes need to stand on the same surface, just like when a ruler begins exactly at zero.
But what if things don’t line up perfectly? Imagine a toy person lying down so that their feet land in the middle of one cube and their head in the middle of another. The trick is to slide the figure mentally to the very edge before you start counting.
The same idea works with a number line. If a little worm rests with its tail at zero and stretches along the line, its length is the number where its head stops. But if the worm starts somewhere else, we can find its length by counting the distance between the starting and ending points — that is, by subtracting the starting point from the ending.
Lines drawn on graph paper make measurement even clearer. You just count the number of little squares a line passes through. These simple tasks quietly prepare kids for a big mathematical idea they’ll meet later — the perimeter, or the total length around a shape.
Measurements
Units of measurement
Measurements
Units of measurement
Measuring with a ruler
Measure length (up to 10)
Measurements
Longer and shorter
Confident Mastery
Indirect Measurement
Sometimes a task gives the height of an object in one kind of unit and asks for it in another.
Imagine a refrigerator that’s as tall as three stools, and each stool is as tall as two boxes. How tall is the fridge in boxes? Kids quickly figure it out: three stools, each made of two boxes, make six boxes in total. That’s their first taste of multiplication, counting groups instead of single items.
Measurements
Units of measurement
The same idea appears when kids use a ruler where not every mark is labeled. They learn to read between the lines, moving in equal steps of two or another fixed size.
Estimation games also grow more interesting. Kids picture what 4 cubes in a row might look like, then 8, then 14, and choose the answer that seems most realistic. It gets trickier when a single cube has a length of 3 instead of 1. Then they imagine what 4 such cubes, a total length of 12, would look like, and again pick the correct option from the choices given.
The hardest puzzles involve strings of beads made of two kinds. Suppose red beads have a length of 1 and yellow beads have a length of 2, and the goal is to make a necklace with a total length of 15. Here division comes to the rescue: one red and one yellow bead together make a block of 3, and to reach 15 you’ll need 5 such blocks.
Measuring with a ruler
Measure length (in 2s)
Units of measurement
Length estimation
Units of measurement
Length estimation
Units of measurement
Indirect measurements
Big Ideas
The idea of measurement lies at the heart of modern science. We measure not only simple things like length, volume, and temperature but also more complex ones such as force, acidity, magnetic fields, or sound levels.
Sometimes what we measure isn’t a physical property at all. A doctor might ask a patient to rate their pain on a scale from 1 to 10. This kind of “measurement” helps capture something subjective, a person’s feelings, and turn it into data that can be tracked and compared.
When we measure something many times, like monitoring heartbeats or daily temperatures, we start to notice how one quantity changes with another. This leads to the idea of a function, a relationship between two variables. Graphs make such relationships visible at a glance.
Converting one unit into another introduces the idea of proportion, which later helps kids understand maps, diagrams, and percentages. And the ability to estimate, to sense roughly how long, heavy, or far something is, remains invaluable even in the age of automation. It keeps our abstract calculations connected to real experience.
