The circle is, in my apprehensive stance, the Queen of the geometric shapes. Don't go me wrong; I like all those squares, rectangles, triangles, octagons, and whatnot; but the circumvolve is the coolest of the bunch: smoothen and pretty and endlessly useful. Notwithstanding, trying to depict a perfect circle without a pattern is a challenge, and figuring out the proper size of an opening into which a circumvolve can exist inserted requires working with Pi (or π), which is not the delicious kind y'all tin can eat with a bit of ice foam. We're here today to help you with the steps y'all've forgotten since high schoolhouse geometry course (or maybe never learned because you were too busy passing notes with Susan Ellery!). We'll show you the parts of a circle, how wide to cut fabric to fit a circle, and how to describe a circle without a blueprint. Nosotros've besides included a handy conversion from decimals to inches, which is necessary when working with Pi.

The parts of a circumvolve

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

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

Bore: the distance across a circumvolve through its centre betoken

Circumference: the distance around the outer edge of a circle

π or Pi: the proper name given to the ratio of a circumvolve's circumference to its diameter, expressed as the decimal 3.xiv

How wide to cut material to fit a circle

If you know the diameter of your circle, you can utilize a standard formula to figure out the width of the cloth cut needed to make a tube. That width is the circumference of the circle that volition be inserted into the tube (nosotros accept a bang-up step-by-step tutorial on how to insert a circumvolve into a tube).

The formula: iii.14 (π) x diameter = circumference

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

3.14 x 12 inches = 37.68 inches

(This works with the metric system likewise: three.14 ten thirty cm = 94.2 cm)

An important step many people miss at this betoken is forgetting to add together extra (to both pieces) for the seam allowance. If yous use a standard ½" seam assart, y'all demand to add i″ to the diameter of your circle ( the diameter increases by double the seam allowance)and 1″ to the width of your textile (½" for both sides of the seam assart). In our example, that means:

The circumvolve should get-go equally 13″ in diameter.

The textile should be 38.68″ in width

The top of your textile cut is variable and dependent on your projection. For example, a tall duffle pocketbook might be 30″ in height whereas a shorter bucket might exist only 10″.

Converting a Decimal to a US Ruler Measurement

If you lot are using Pi, recall it always returns a decimal number. If you already deal with the metric system, you rock –  no conversion necessary.

For those of u.s.a. in the world of inches, y'all demand to notice a yardage conversion.

In our example nosotros have 38.68 inches. Harumph! The table below volition requite yous a close-enough ruler lucifer.

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

How to Draw a Circumvolve

If you accept a supply of large compasses, yous're in luck, and can easily draw yourself all sizes of circles. But you can also easily brand your ain compass to draw a circle.

To first, y'all demand to know how large you want your circumvolve (the bore). For our ongoing case, we want a 13″ diameter circle

To draw a circle y'all need to know its radius. As y'all learned higher up in the first section, the radius is one half of the diameter. In our case, one half of 13″ is six½".

The full circle method

  1. Utilise a sheet of lightweight paper (graph or blueprint paper works well) that is at to the lowest degree i″ larger all effectually than the circumvolve you want to depict.
  2. Cut a slice of string virtually 4″ – 5″ longer than your radius. We used a ten″ length of string.
  3. Tie 1 finish of the string to a short pencil.
  4. Identify the indicate of the pencil toward the outer edge of the paper with plenty room from the border to make a full sweep.
  5. Mensurate from where the point of the pencil touches the newspaper backwards by the length of the radius (in this example 6½").
  6. Pin directly through the string into the newspaper at that exact point.
  7. Keeping the string taut, depict a perfect circle using your homemade compass.

The folded quarters method

  1. Over again, commencement with a square of lightweight paper at to the lowest degree 1″ larger than the circle you lot want to describe.
  2. Fold the paper into quarters. Make sure your original foursquare is even and true! Position the paper with its folded edges along the bottom and left side and the open edges along the top and right side.
  3. Place a see-through ruler at the verbal middle of the bottom left corner of your folded square. Swing the ruler from the elevation to the bottom of the square, like a pendulum or compass, measuring and marking a dot at the 6½" point in three to four spots. You are creating a semi-circle arc. Brand sure the end of the ruler at the corner point doesn't shift position.
  4. Cut along the arc through all the layers and unfold the finished 13″ circumvolve. Yous can now use this paper pattern to cutting your fabric circle.

With your spiffy new circle, y'all can now run up the side seam in the main fabric cutting. So pin the base to the resulting tube and sew together the tube to the circle using a ½" seam assart. The result is a 12″ diameter finished base of operations.

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