How to Measure Tree Size
Trees can range from small saplings to giant redwoods that reach over 300 ft (91 m) high. You might think measuring trees is a hard job, but it’s actually pretty simple and only requires some basic tools. With only measuring tape, you can calculate the circumference and diameter of any tree. With a few extra steps, you can measure the average crown spread, or the extent of the branches and leaves. You can also estimate the height of a tree with a few different methods. Whether you're planning construction on your property, working in forestry, or just looking for a fun activity, then grab some measuring tape and get started!
Calculating Circumference and Diameter on Standard Trees

Measure 4.5 ft (1.4 m) straight up from the ground level. This height is the standard for measuring trees. Place a ruler or measuring tape at the tree’s ground level. Then extend it up until you reach 4.5 ft (1.4 m) up the tree trunk. Mark this spot with a thumb tack or piece of tape.
 When you calculate the diameter at this level, it’s called diameter at breast height (DBH). This is the standard measurement for tree size.
 If the tree has any growths or abnormalities that will increase its diameter at breast height, then measure just below the growth.

Wrap measuring tape around the trunk at the 4.5 ft (1.4 m) mark. Hold the measuring tape level against the trunk. Then hold the end of the tape in place with one hand and wrap the rest of it around the trunk. Pull the tape tight and record the measurement where the tape overlaps. This gives you the simple circumference of the trunk.
 Make sure the tape stays level around the tree. If it shifts, your measurement will be too big.
 If the tree is very large, work with a partner to hold the tape while you wrap it around. If you’re alone, try taping or thumbtacking the end of the measuring tape in place while you wrap it around.
 You can use a string or twine if you don’t have measuring tape. Wrap it around the tree as if you had measuring tape and mark on the rope where it overlaps its tip. Then use a ruler to measure the length of that section to get the circumference.

Divide the measurement by pi (3.14) to get the diameter measurement. The tree trunk measurement is a simple circumference. You can use this measurement to figure out the trunk diameter. Simply divide that measurement by pi (3.14) and the result is the diameter.
 For example, if you measured the trunk at 24 in (61 cm), then the calculation is 24/3.14. The result is 7.6, meaning that the diameter is 7.6 in (19 cm).
Measuring the Circumference on Irregular Tree Trunks

Find the thinnest point below a split if the tree trunk divides. Some tree trunks split into 2 separate sections. If this happens below the 4.5 ft (1.4 m) mark, then find the thinnest trunk portion below the split. Take your circumference measurement here.
 The reason you have to find the thinnest portion is because trunks often start getting wider just below a split. If you measure directly below the split, your measurement might be too big.

Measure along the tree’s angle if it grows diagonally. Sometimes trees grow at an angle, so keeping the tape level around the trunk will make your measurement too big. First, measure along the tree trunk to find the 4.5 ft (1.4 m) mark instead of measuring straight up from the ground. Then, angle your tape along with the tree and wrap it around the trunk for an accurate measurement.
 Only measure at an angle if the tree itself is growing at an angle. If the ground is sloped but the tree is growing straight, then still take your measurement straight up the trunk.

Take a measurement from the widest trunk on multistemmed trees. Some trees split into multiple stems without leaving much of a trunk below to measure. In this case, pick the widest stem and take the circumference of that one at 4.5 ft (1.4 m) high. Use this measurement to calculate the diameter.
 Sometimes separate trees can fuse together, meaning that the different trunks are actually different trees. It’s tough to tell whether a multistemmed growth is a single tree or multiple trees, so you'll have to make a judgement call. The bark may look like it fused together in some spots, indicating that this is multiple trees.
 If it is multiple trees, then take a measurement of every stem individually instead.
Figuring Out the Average Crown Spread

Mark the spot where the crown extends the furthest from the tree trunk. Walk around the tree and find the spot where the tree’s branch spread is the furthest. Stand directly under that point and place a marker there.
 The marker you use doesn’t matter. It could be a rock or stick. You could also hammer some stakes into the ground so the markers are easier to see.
 Don’t use anything that will blow away as your marker. A piece of paper won’t work.
 The crown of a tree is its branches and leaves. The crown spread is the average horizontal width of the crown.

Place a marker where the crown ends on the other side of the tree. Walk straight across the tree from your first marker and find the spot where the crown ends. Place a marker there as well.
 Make sure your second marker is directly across from the first one, otherwise your measurements will be off.
 If you have a partner, you can make this easier by standing in one spot holding the measuring tape while your partner walks to the other side. That way, you’ll get the measurements immediately without having to use markers.

Put 2 more markers 90 degrees from the first ones to make a square. Once you’ve placed the first 2 markers, then rotate 90 degrees to the other side of the tree. Find the spot where the crown ends and place a marker at that point. Finally, walk directly to the other side of the tree and find where the crown ends. Place a final marker at this point.
 Remember to make sure the markers are all straight across from each other.

Measure the axis between the markers. First, take the distance between the first 2 markers you placed down. Then measure the distance between the second set of markers. Record both measurements so you don’t forget them.
 Unless the tree is very small, it’s best to use feet or meters for these measurements. Inches and centimeters are too small.
 A vinyl tape roll is best for this task since you’ll be measuring longer distances.

Add up the measurements and divide the total by 2. Once you have your 2 axis distances, then finding the average crown spread is easy. Simply add the 2 measurements together and divide by 2.
 For example, your axis measurements may have been 20 feet (6.1 m) and 15 feet (4.6 m). Add those measurements to get 35 feet (11 m), then divide by 2 to get 17.5 feet (5.3 m). This is the tree’s average crown spread.
Tips
 Almost all of these tasks are easier with a partner. Bring someone along to make the job go by much faster.
Warnings
 Stay away from trees that look rotten or dead. These are weak and could fall over.
Things You’ll Need
 Measuring tape
 Bright tape or ribbon
 Stakes or rocks for markers
 Paper and pencil for calculations
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