The circle is, in my apprehensive opinion, the Queen of the geometric shapes. Don't get me wrong; I similar all those squares, rectangles, triangles, octagons, and whatnot; simply the circle is the coolest of the bunch: smooth and pretty and endlessly useful. However, trying to draw a perfect circle without a blueprint is a claiming, and figuring out the proper size of an opening into which a circumvolve tin can be inserted requires working with Pi (or π), which is not the delicious kind you can swallow with a bit of water ice cream. We're here today to help you with the steps you've forgotten since high school geometry class (or peradventure never learned because y'all were also busy passing notes with Susan Ellery!). We'll bear witness y'all the parts of a circumvolve, how broad to cut fabric to fit a circle, and how to draw a circle without a design. We've also included a handy conversion from decimals to inches, which is necessary when working with Pi.

The parts of a circle

Let'due south commencement with remembering what all the parts of a circle are called and how Pi (π) fits into the mix.

Radius: the distance from the center of the circle to the outside edge

Diameter: the distance across a circle through its centre bespeak

Circumference: the distance around the outer edge of a circle

π or Pi: the name given to the ratio of a circle's circumference to its diameter, expressed every bit the decimal 3.fourteen

How wide to cut textile to fit a circle

If you know the diameter of your circle, you can use a standard formula to figure out the width of the fabric cut needed to brand a tube. That width is the circumference of the circle that will be inserted into the tube (nosotros have a great pace-by-step tutorial on how to insert a circumvolve into a tube).

The formula: 3.14 (π) x diameter = circumference

Example: You desire a finished 12″ bore base (a 12″ diameter circle) in a duffle bag.

iii.xiv x 12 inches = 37.68 inches

(This works with the metric system besides: 3.14 x xxx cm = 94.2 cm)

An important stride many people miss at this indicate is forgetting to add extra (to both pieces) for the seam allowance. If you use a standard ½" seam assart, you need to add 1″ to the diameter of your circle ( the diameter increases past double the seam assart)and 1″ to the width of your fabric (½" for both sides of the seam allowance). In our example, that means:

The circle should start equally 13″ in diameter.

The textile should be 38.68″ in width

The height of your fabric cutting is variable and dependent on your project. For instance, a alpine duffle bag might be 30″ in height whereas a shorter bucket might exist just 10″.

Converting a Decimal to a US Ruler Measurement

If you are using Pi, remember it e'er returns a decimal number. If yous already deal with the metric organisation, yous stone –  no conversion necessary.

For those of usa in the globe of inches, yous need to find a yardage conversion.

In our instance nosotros have 38.68 inches. Harumph! The table below will requite y'all a close-enough ruler match.

The decimal .68 is closest to .63 or ⅝". We can use 38⅝" equally the width of the cloth piece you are cutting for your tube.

How to Draw a Circle

If you have a supply of large compasses, you're in luck, and tin can hands depict yourself all sizes of circles. Simply yous can besides easily make your ain compass to describe a circle.

To start, y'all need to know how big you lot want your circle (the diameter). For our ongoing example, we want a 13″ diameter circumvolve

To describe a circle you demand to know its radius. As you learned in a higher place in the kickoff section, the radius is one half of the diameter. In our example, ane one-half of thirteen″ is 6½".

The total circle method

  1. Use a sail of lightweight paper (graph or pattern paper works well) that is at least ane″ larger all around than the circle yous want to describe.
  2. Cut a slice of string nearly four″ – 5″ longer than your radius. Nosotros used a 10″ length of string.
  3. Tie one stop of the string to a short pencil.
  4. Place the point of the pencil toward the outer border of the newspaper with enough room from the border to make a full sweep.
  5. Measure from where the point of the pencil touches the newspaper backwards by the length of the radius (in this case half dozen½").
  6. Pin straight through the string into the paper at that exact point.
  7. Keeping the string taut, draw a perfect circumvolve using your homemade compass.

The folded quarters method

  1. Again, starting time with a square of lightweight paper at least 1″ larger than the circumvolve you desire to draw.
  2. Fold the paper into quarters. Make sure your original foursquare is fifty-fifty and true! Position the paper with its folded edges along the lesser and left side and the open edges forth the elevation and right side.
  3. Place a see-through ruler at the verbal eye of the lesser left corner of your folded foursquare. Swing the ruler from the top to the lesser of the foursquare, similar a pendulum or compass, measuring and marking a dot at the six½" bespeak in iii to four spots. You are creating a semi-circle arc. Make certain the end of the ruler at the corner signal doesn't shift position.
  4. Cutting along the arc through all the layers and unfold the finished 13″ circumvolve. Yous can now use this paper design to cut your fabric circle.

With your spiffy new circumvolve, you can now run up the side seam in the principal fabric cut. Then pin the base of operations to the resulting tube and sew the tube to the circle using a ½" seam assart. The result is a 12″ diameter finished base.

As mentioned to a higher place, for more on this technique, encounter our tutorial: How to Insert a Flat Circle Into a Tube.