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Human Body Ratios

Author(s): Nancy Moreno, PhD, Barbara Tharp, MS, and Sonia Rahmati Clayton, PhD.
Human Body Ratios

© Nikita Vishneveckiy.

  • Grades:
  • Length: Variable


Students practice estimating and measuring in metric units, and investigate the concepts of ratio and proportion as they relate to features of the human body. 

As part of this activity, students visit the PowerPlay exhibit at the Children's Museum of Houston. This lesson is best conducted after after going to the Museum.

This activity is from the PowerPlay Teacher's Guide. Although it is most appropriate for use with students in grades 3-7, the lessons are easily adaptable for other grade levels.

The PowerPlay project is a partnership between Baylor College of Medicine and the Children's Museum of Houston.

Teacher Background

Measuring, an essential skill for all students, is the focus of this Children’s Museum of Houston’s PowerPlay station (, which allows individuals to measure their height and weight. In addition to completing the station, students are encouraged to track changes in their height and weight over time by logging into their own private, web-based PowerPlay accounts (

Have you ever heard the sayings, “Once around the waist, twice around the neck,” or “Once around the neck, twice around the wrist?” In this activity, students will investigate simple proportional relationships among the measurements of various body parts. For example, consider the following correlations for an average adult (may vary somewhat for children).

  • Total height is equivalent to 7 to 7.5 heads tall

  • Nose length is equivalent to first two digits of index/pointer finger

  • Head is approximately four to five eyes wide

  • Length of face is equal to length of hand

  • Eyes are separated by one eye’s width

  • Bottom of nose to outside corner of eye is equal to length of ear

  • Length of foot is equal to length of forearm

  • Waist to neck ratio is 1 to 2 (waist is twice the circumference of the neck)

  • Neck to wrist ratio is 1 to 2 (neck is twice the circumference of the wrist)

Objectives and Standards

Texas Essential Knowledge and Skills (TEKS) Objectives


3.2.A-F; 4.2.A-F; 5.2.A-F

  • Student uses scientific inquiry methods during laboratory and outdoor investigations.

3.4.A-B; 4.4.A-B; 5.4.A-B

  • Students know how to use a variety of tools, materials, equipment, and models to conduct science inquiry.

3.2.B; 4.2.B; 5.2.B

  • Students collect data by observing and measuring using the metric system and recognize differences between observed and measured data.

Materials and Setup

Materials per Student

  • Flexible metric tape measure

  • Small mirror

  • Student worksheets

Procedure and Extensions


One or two 45-minute class periods


  1. Ask students, How long is your foot? Did you know there is a way to estimate this length without even looking at your foot? Does anyone know the secret?

  2. Call a volunteer student to the front of the room. Measure the length of that student’s forearm. Then instruct each student measure his/her own forearm in the same way. Have students compare their forearm measurements to the heal-to-toe length of one of their feet. The two measurements should be very close.

  3. Ask students if they think other body parts might have similar sizes, or if there might be other predictable ratios between the sizes of different body parts. Mention that students will investigate a number of body measurements and determine some possible relationships among them.


  1. Before beginning, review with the class how to use a tape measure.

  2. Distribute the “Estimates and Measures” student sheet. Have each student estimate his or her height in centimeters and record that number on the first line in the “Estimate” column. Next, instruct students use a tape measure to measure their height accurately and record that number on the appropriate line in the “Actual” column.

  3. Have students estimate, then measure the next body dimension (arm span) listed on the student data sheet. Students should continue in this manner until are measurements are completed.

  4. Direct students to look for patterns and relationships among their measurements. For instance, ask, How does the length of your nose compare with the width of the first two digits of your pointer finger?


  1. Ask, Did the estimates you recorded for the size of each body part become more accurate as you continued making measurements? Why might this be the case?

  2. Ask students if any of their measurements are equal, half, double, or 1.5 times the length of any of the other measurements. (For example, the length of most people’s foot is equal to the length of their forearm.) If so, what are they?

  3. Have the class form student groups of 4. Have each group calculate and record the average measurement of each body part for their group in the “Group Average” column and then compare the team average to individual measurements.


  1. Distribute the “Human Body Ratios” student sheet. Have students use information from the “Actual” column in the “Estimates and Measures” student sheet to complete column one.

  2. Ask students if they notice measurement patterns and relationships that are common to all groups.


  1. At 2.72 meters (8 ft, 11 in.) in height, Robert Pershing Wadlow was the tallest man in recorded history. Ask students, Based on the relationship of one body part to another on your completed “Human Body Ratios” sheet, what would his estimated arm span and head size be?

  2. Ask students if they ever have heard the old saying, “Once around the waist, twice around the neck; once around the neck, twice around the wrist.” Have them determine if this statement is true for themselves and other members of their groups.

Handouts and Downloads


Science Education Partnership Award, NIH

Science Education Partnership Award, NIH

Grant Number: R25RR022697