How to Calculate Girth

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Standard measurements include length, width, volume, weight and mass. Girth, however, is equally as important as those standard measurement calculations in a variety of applications and fields.

Whether you're a scientist studying tree growth or trying to send your friend a package in the mail or a person looking for the right clothing size for your dog, you need to know what's a girth measurement and how to calculate it.

Girth Definition

"What's a girth?" you might be wondering. It's not really a thing at all; it's a type of measurement.

Girth measures the circumference around the widest point of a generally cylindrical shape or object. This could be anything from a poster package to an animal to a tree to a bottle of soda.

How to Calculate the Girth Measurement

Girth is most often calculated using string or a fabric ruler. Depending on what you're measuring, you usually try to find its widest point. This is often the middle of an animal or an inanimate object. For trees, a good rule of thumb is to measure five feet up from the group on the upwards side of any slope.

If you're using a fabric ruler, simply wrap the ruler around this point of the object/animal/person you're using and record the measurement. Make sure that the ruler is pulled tight enough that it isn't loose or
"falling" off of the object, but not too tight to make the measurement less than it actually is.

If you're using string, wrap the string around the object/animal/person. Mark the string with a marker or pen at the point where the string comes full circle around your subject and is touching the string where you started.

Then, you can use a ruler to measure that length of string from the end to the marked point to get the girth measurement. This type of measurement can be used in a variety of fields and applications.

Packages and Parcels

Perhaps the most common and widespread use of this measurement is for use in sending packages and parcels. Many shipping and mailing businesses will charge based on the parcel measurements including weight, size and girth.

In this case, it isn't always a cylindrical package. Packaging and shipping companies refer to girth with its more general definition as the measurement that measures around the entire object.

Tree Size and Growth

Besides height, girth of the tree trunk is one of the main ways for scientists to measure and track tree growth. Scientists usually measure 4.5 to 5 feet up the tree for the most accurate girth measurement.

According to the Tree Register website, young trees should be measured yearly while mature trees only need to be measured every five to 10 years.

Body Fat Percentage

Calculating body fat percentage can be an important indicator of health. It's also important for professional weightlifters and bodybuilders to keep track of. To calculate percent body fat, various girth measurements are taken along with height. Different measurements are taken based on gender.

Males require girth measurements of the neck and their abdomen. Females require girth measurements of the neck, waist and hips. Then you use the following equations based on the gender of the subject:

Male body fat percent = 86.010 x log10(abdomen girth - neck girth) - 70.041 x log10(height) + 36.76

Female body fat percent = 163.205 x log10(waist girth + hip girth - neck girth) - 97.684 x log10(height) - 78.387

Sports Applications

Girth is also relevant in sports such as fishing and hunting. Girth is an important measurement for sport fishing and hunting to measure the size of the catch. You can also use girth to measure sporting equipment like baseball bats.

References

About the Author

Elliot Walsh holds a B.S in Cell and Developmental Biology from the University of Rochester. He's worked in multiple research labs, as a TA for chemistry, and as a tutor in STEM subjects. He's currently working full-time as a content writer and editor for clients in niches including marketing, science, health, nutrition, and LGBTQ+ topics.

Photo Credits

  • Michael Blann/Digital Vision/Getty Images

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