Circumference Calculator - Circles
Calculate the circumference of a circle, which is the perimeter going all the way around the object. Circular shapes abound in pottery, plates and bowls among the most popular. Knowing the circumference helps when hand building slabs, so you roll out slabs or make coils long enough to ideally encircle the piece without joins.
Circumference Calculator - Entry Fields
Measure Length - Enter the length of either the diameter or radius, in your selected Unit of Measure.
Circle Measure - Indicate if the Measure Length entered represents the circle's diameter or radius. Diameter is the distance measured from one side of the circular object to the other, passing through the center. Radius is half of that, measuring from the center to object's circumference edge.
Unit of Measure - Indicate unit of measure for the radius or diameter length you've entered.
What is the Circumference of a Circle?
If you could completely unwind a circle, such that you formed a straight line, the length of that line from the starting point to the end point is its circumference.
Put another way, a circle's circumference is the length of the perimeter going all the way around it, from a specific starting point going completely around it (i.e. all 360 degrees).
Circular objects are everywhere in our everyday. A coin is round has a circumference. Many food cans are round and have a circumference. A car's steering wheel has a circumfernce. And many pottery shapes are circular: A round ceramic plate, a round ceramic bowl, a round ceramic vase.
Most round pottery likely has multiple circumferences. For example, if the diameter of a bowl's bottom and top differ, which is usually the case, it has at least 2 circumferences, more if it tapers.
What is the Formula for Circumference of a Circle?
Circumference = 2 * r * π
where r=radius
To calculate circumference, multiply the radius by 2 (which is the diameter), and then multiply by Pi which is approximately 3.14.
An alternate way to calculate is:
Circumference = d * π
where d = diameter.
This calculator lets you choose if you want to calculate with radius or diameter. Often, it is easier to measure the diameter of a pottery piece than the radius.
Find out more about π (pi) below.
Why Calculate Circumference of Round Pottery Pieces?
Knowing the circumference of round pottery can be extremely helpful, particularly when hand-building:
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Knowing Length of Slab to Roll
If you are hand-building with slabs, knowing the circumference of the base of the pottery piece enables you to know how much clay to roll out, especially if you prefer to avoid additional joins on the sidewall.
For example, if you are hand-building a bowl and have cut out the circular base, calculate its circumference, which will tell you how long the slab for the side needs to be. If your slab is at least as long as the circumference, you'll only have 1 join.
Even if you will use multiple slabs for the sidewalls, scoring each together, knowing the circumference will let you know how much clay to roll out. As we all know, running short on slab pieces can be a hassle, especially since you have to quickly roll out more clay, and your pieces are then in different plasticity/workability stages.
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Knowing Length of Coils to Roll
If you're making a pottery bowl, or other round piece, with coils, knowing the circumference will help determine how long the coil needs to be for the next section.
As with clay slabs, if you prefer not to have multiple joins in a given coil row, the circumference informs you of the minimum length the coil should be. Of course, if you are expanding outward as you coil up the piece, you need to roll out the circumference length plus an added amount; if contracting inward, you'd need a bit less.
If your coiled pottery piece will have a uniform diameter from base to top, circumference is very handy, so you will know the length of each coil you roll out or extrude.
What is Pi π and what's the Pi connection to circles?
Who doesn't love a good piece of Pi, especially pecan or apple a la mode?!
Pi, whose mathematical symbol is π, has been around for about 4,000 years, and is an important constant used in geometry pertaining to circles and ellipses.
Most often it is seen as the constant 3.14 or 3.14159, but it's an irrational (never-ending, non-repeating) number. In 2024, it took a super computer 75 days to calculate Pi out to 105 trillion digits!
Pi and Circles
Here's a fascinating fact about circles: if you measure the circumference of a circle and divide it by its diameter, you will end up with a number approximately equal to 3.14!
It doesn't matter how large or small the circle is:
π ≅ C/d
where:
C = Circumference, d = Diameter
Keep in mind that using π yields an approximation, albeit a very close once, since an abbreviated form is used as the constant.
Pi is used everywhere, essential to our understanding of our world as well as outer space.
No two ways about it - Pi is a cool number. So much so that March 14th is Pi Day, started in 1988 by physicist Larry Shaw.
Why March 14th? March is Month 3: 3.14 !