How to work out the age of a living tree as a fun summer holiday activity
17th July 2021

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You can find giant historic trees all over the UK and many have been standing for hundreds and hundreds of years. If you’ve ever wondered exactly how old these towering trees are, there are a multitude of ways that you can find out.

No, it’s no old wives’ tale, you can in fact work out the age of a tree by counting its rings. Every year, each tree develops a light ring of new growth to its trunk during the spring and summer months when it is at its optimum growing time.

A darker, thinner ring is also developed in the autumn when the growing process slows. One year of the life of a tree will equal one light ring and one dark ring.

When the temperature is just right for the tree, as is the right level of rain, the tree will grow faster and therefore produce wider rings. If conditions are not ideal for growth, trees will grow to a slower pace and the rings will subsequently be thinner.

It’s a great one to get the kids involved with counting tree rings (also known as growth rings) if you ever stumble across a tree stump. However, make sure that you are only counting either the light rings or the dark rings, not both as otherwise you would be doubling up on the age of the tree.

In addition to dating them, scientists can gather data for both climate and atmospheric conditions during different periods in history, obtained from wood.

Scientists don’t even have to cut down trees in order to obtain these readings from trunks, they can instead use an increment borer to carve out a small chunk, no wider than a pencil, to view the findings. This won’t damage the tree.

If, like the majority of us, you don’t happen to have an increment borer lying around at home, you can calculate the age of a living tree using simple maths.

It may not give you an exact age of the tree, but it certainly will be a rather close measurement. You will be using a few mathematical terms for this endeavour, they are:

Circumference: The measurement of the outside of a circle
Diameter: The measurement of a circle’s width, or distance from edge to edge, measuring through the centre
Pi: In this particular instance, we are taking the value of Pi to be 3.14

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You will need to wrap a sewing tape measure around a tree trunk around 4.5ft off of the ground. In the absence of a tape measure, you can use string and use a ruler to determine how long the measured string is. Try to avoid any lumps and bumps in a trunk.

This measurement will be the tree’s circumference. 


Take the circumference measurement of the tree to find its diameter. The formula for finding diameter is the circumference divided by Pi (3.14).


You need to identify the type of tree that you are measuring. This is so that you can find the growth factor of the tree – different trees grow at very differing rates.

Below are a few examples of the average growth rates for typical trees that can be found in the UK:

Oak and beech 1.88cm

Pine and spruce 3.13cm

Sycamore 2.75cm

Once you find the average growth rate, you can determine the age of the tree by multiplying the diameter by the growth factor. And there you have it, it couldn’t be easier.

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