How Big is Your Tree?

Tall tree

How Big Is Your Tree (Adapted lesson of Project Learning Tree): In this activity, students will measure trees in different ways and become familiar with the tree’s scale and structure. They will also learn the importance of standard units of measurement and measuring techniques. 


• Blank piece of paper
• Measuring tape or ruler or large ball of string
• Large sheet of paper
• Copy of student pages
• Ideal trees are in open spaces so students can measure the trees shadow

Doing the Activity:

  1. Have your students discuss why people measure things and in what ways do they measure them.
  2. Ask students why some people want to measure a tree (foresters measure trees to plan harvesting or to decide on other forest management practices)
  3. Take students outside and have them choose a tree that they will measure (if possible, have students pick a tree that will have a measurable shadow. If this is not available, that is okay, there is another way to measure the height of the tree). Ask them to estimate the circumference of the tree trunk (in inches or centimeters) and then have them measure it in arms spans (wrapping arms around the trunk) — if the tree is smaller, they can measure with their hands. Record measurements on your data sheet.
  4. Have students measure the circumference with either the string (which you can use as a way to measure) or the measuring tape. Record measurements on data sheet. Compare all three measurements (estimates, arm/hand spans, standard measurement).
  5. Explain that foresters always measure a tree at 4.5 feet off the ground, this is referred to as the DBH, or Diameter At Breast Height. To show why it is important to have a standard of measurement, ask students to measure the trunk of the tree at 1 ft from the ground, then 2ft, then 4.5 feet. Have a quick discussion as to why they think foresters measure all trees at 4.5 feet. What would happen if everyone measured the circumference of a tree at different heights?
  6. On a sunny day, have students determine the height of a tree by measuring the length of the shadow (see illustration 2 on student page. If the tree does not have a shadow, move on to step 7). First, students will measure their own height and the length of their shadow at the same time of day. Have students use this ratio comparison to determine the height of the tree:

Tree’s height = Students height x Tree’s shadow / Students shadow

If you have more than one student, have them compare their calculations. What might explain any differences?

  • If there are no shadows at the time of this activity, you can do a proportional method of measuring (see illustration 1 on student page). Have a student (or adult if there is only one student) stand at the base of the tree to be measured. Hold a ruler at arm’s length and walk backwards, keeping arm straight, until the top and bottom of the ruler line up with the top and bottom of the tree. Note where the top of the person’s head is in relation to the ruler (for example, 2 in. or 4 in. marker). Divide the length of the ruler by this figure (12 in ÷ 2 in = 6). Then, measure the students actual height, and multiply it by this figure (i.e., 6). For example, if the student is 55 inches tall, you would do 55 x 6 = 330 (27.5 feet).You have found how tall the tree is!
  • Back inside, your students can make graphs or diagrams to create a visual summary of the results.

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