The circle is, in my humble opinion, the Queen of the geometric shapes. Don't become me wrong; I like all those squares, rectangles, triangles, octagons, and whatnot; just the circumvolve is the coolest of the bunch: polish and pretty and incessantly useful. However, trying to draw a perfect circle without a pattern is a challenge, and figuring out the proper size of an opening into which a circle tin be inserted requires working with Pi (or π), which is not the delicious kind you can consume with a bit of ice cream. We're here today to help y'all with the steps you lot've forgotten since loftier school geometry class (or maybe never learned considering you lot were besides decorated passing notes with Susan Ellery!). Nosotros'll show you the parts of a circle, how broad to cutting material to fit a circle, and how to draw a circumvolve without a design. We've as well included a handy conversion from decimals to inches, which is necessary when working with Pi.

The parts of a circle

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

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

Diameter: the distance across a circumvolve through its center bespeak

Circumference: the distance around the outer border of a circle

π or Pi: the name given to the ratio of a circle'southward circumference to its diameter, expressed as the decimal 3.14

How wide to cut textile to fit a circle

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

The formula: 3.14 (π) ten bore = circumference

Example: Y'all want a finished 12″ bore base (a 12″ diameter circle) in a duffle pocketbook.

3.14 x 12 inches = 37.68 inches

(This works with the metric system equally well: three.14 x 30 cm = 94.2 cm)

An important stride many people miss at this point is forgetting to add extra (to both pieces) for the seam allowance. If you use a standard ½" seam allowance, you lot need to add i″ to the diameter of your circumvolve ( the bore increases by double the seam allowance)and i″ to the width of your cloth (½" for both sides of the seam allowance). In our instance, that means:

The circle should starting time every bit 13″ in diameter.

The cloth should be 38.68″ in width

The meridian of your fabric cutting is variable and dependent on your project. For example, a alpine duffle pocketbook might be 30″ in height whereas a shorter bucket might be only 10″.

Converting a Decimal to a Usa Ruler Measurement

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

For those of usa in the world of inches, you need to observe a yardage conversion.

In our example we have 38.68 inches. Harumph! The table beneath will give you a close-enough ruler match.

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

How to Describe a Circle

If y'all have a supply of big compasses, you're in luck, and can easily depict yourself all sizes of circles. But you can also hands make your own compass to draw a circumvolve.

To get-go, you need to know how big you desire your circle (the bore). For our ongoing example, we want a xiii″ bore circumvolve

To depict a circle you need to know its radius. As yous learned above in the first section, the radius is i half of the bore. In our case, one half of thirteen″ is 6½".

The full circumvolve method

  1. Employ a canvas of lightweight paper (graph or pattern paper works well) that is at least 1″ larger all around than the circle you want to draw.
  2. Cut a piece of cord most 4″ – 5″ longer than your radius. We used a 10″ length of string.
  3. Tie i end of the string to a short pencil.
  4. Place the betoken of the pencil toward the outer border of the newspaper with enough room from the edge to make a total sweep.
  5. Measure from where the betoken of the pencil touches the newspaper backwards past the length of the radius (in this case six½").
  6. Pin directly 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. Over again, start with a square of lightweight paper at least 1″ larger than the circle you want to draw.
  2. Fold the paper into quarters. Make sure your original square is even and truthful! Position the paper with its folded edges along the lesser and left side and the open edges along the top and right side.
  3. Identify a see-through ruler at the verbal center of the bottom left corner of your folded square. Swing the ruler from the summit to the bottom of the square, like a pendulum or compass, measuring and marking a dot at the six½" point in three to four spots. Yous are creating a semi-circle arc. Brand sure the end of the ruler at the corner signal doesn't shift position.
  4. Cut along the arc through all the layers and unfold the finished 13″ circle. You can now employ this newspaper pattern to cut your fabric circle.

With your spiffy new circle, you can now run up the side seam in the main material cutting. Then pin the base to the resulting tube and sew the tube to the circle using a ½" seam allowance. The event is a 12″ diameter finished base of operations.

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