You need: a pencil (or a straight stick) and a friend.
STEP ONE: Stand far enough back to see the whole tree.
STEP TWO: Hold your arm straight out in front of you. Hold the pencil upright. Slide your thumb on the pencil until the pencil length between thumb and tip visually matches the tree height (thumb lines up with the base; pencil tip with the top).
STEP THREE: Keeping your thumb fixed, rotate your wrist so the pencil lies horizontal and the pencil's “height” now points along the ground towards the tree.
STEP FOUR: Ask a friend to walk to the spot where the pencil tip is.
STEP FIVE: Ask the friend to take large steps towards the tree. Count the number of steps until they get to the trunk.
STEP SIX: Use the number of steps to calculate the size of the tree. 1 big pace ≈ 0.75 metres. So if it is two steps, the tree height will be 1.5m. If you're struggling, use our height calculator.