Math in the Garden – Measuring Trees
Yesterday we measured the trees in our little food forest to record growth and to bring what we’re learning in our math curriculum out to our real world in the garden.
In this activity kids can practice measuring and can further understand terms like perimeter, circumference and diameter.
Of course, you don’t need your own garden or tree for this activity. Walk out your street or to the nearest park to find some tree friends to measure!
Why do we measure trees?
For us measuring trees might not have many real life uses, but it was a fun way to practice measuring circumferences. We are curious to see how the numbers change in one year and if that might allow us to predict their size over time. But in professional forests there are many reasons why measuring trees is important. Some of those reasons are that it allows them to estimate the tree’s age, determine how much fertilizer to use, and calculate the value of the wood before cutting it.
What you’ll need:
Measuring tape
String
Notepad and pencil
How are trees measured?
The standard way to measure a tree is by their diameter at “breast height”, often referred as DBH. The diameter is a straight line passing from side to side through the center of the trunk and breast height refers to finding this measurement at 4.5 ft above the ground.
In short, we’ll measure the circumference of a tree at 4.5 ft of height and then use that number to calculate the diameter.
To calculate the diameter of a tree, you will take the circumference of the circle and divide it by π.
Measure the circumference of the tree trunk at 4.5 F above the ground. Then take that measurement and divide it by Pi to get the diameter.
My second grade student isn’t calculating diameter yet, nor is she dividing or understanding Pi, so we measured the circumference and left it at that.
We laid the string on the ground to measure the tree’s circumference with a measuring tape.
Steps to measure a tree
Measure 4.5 ft above the ground, that’s where you’ll measure your circumference. If your tree is younger and/or branches out before reaching 4.5 ft. then you’ll want to find the smallest circumference just below the branches and measure there.
Wrap your string around the trunk and mark when it overlaps.
Measure the length of the string with your measuring tape and record the number to compare with next year’s numbers.
To find the diameter, use the formula D=C/π
