The circumvolve is, in my humble opinion, the Queen of the geometric shapes. Don't get me wrong; I like all those squares, rectangles, triangles, octagons, and whatnot; simply the circumvolve is the coolest of the bunch: polish and pretty and endlessly useful. However, trying to draw a perfect circle without a pattern is a claiming, and figuring out the proper size of an opening into which a circumvolve tin exist inserted requires working with Pi (or π), which is not the delicious kind you can swallow with a bit of ice cream. We're here today to assistance you with the steps you've forgotten since loftier school geometry class (or maybe never learned because yous were too busy passing notes with Susan Ellery!). We'll testify you the parts of a circle, how wide to cutting material to fit a circle, and how to describe a circle without a pattern. We've likewise included a handy conversion from decimals to inches, which is necessary when working with Pi.

The parts of a circle

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

Radius: the altitude from the centre of the circumvolve to the outside edge

Diameter: the altitude beyond a circle through its center signal

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 bore, expressed every bit the decimal 3.fourteen

How wide to cut cloth to fit a circle

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

The formula: iii.xiv (π) ten diameter = circumference

Case: You want a finished 12″ diameter base (a 12″ diameter circle) in a duffle purse.

3.fourteen x 12 inches = 37.68 inches

(This works with the metric organisation too: three.14 x 30 cm = 94.2 cm)

An important step many people miss at this signal is forgetting to add actress (to both pieces) for the seam allowance. If you use a standard ½" seam allowance, you demand to add one″ to the bore of your circle ( the diameter increases by double the seam assart)and 1″ to the width of your cloth (½" for both sides of the seam allowance). In our example, that means:

The circle should start as 13″ in diameter.

The fabric should be 38.68″ in width

The peak of your cloth cut is variable and dependent on your project. For instance, a alpine duffle pocketbook might be 30″ in height whereas a shorter bucket might be only 10″.

Converting a Decimal to a United states of america Ruler Measurement

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

For those of usa in the earth of inches, you demand to find a yardage conversion.

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

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

How to Describe a Circumvolve

If you lot accept a supply of large compasses, yous're in luck, and can easily draw yourself all sizes of circles. Merely you can also easily make your own compass to describe a circumvolve.

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

To describe a circumvolve you lot need to know its radius. As you learned higher up in the beginning section, the radius is 1 one-half of the bore. In our example, 1 one-half of 13″ is 6½".

The full circle method

  1. Use a sheet of lightweight paper (graph or pattern paper works well) that is at least 1″ larger all around than the circumvolve you desire to draw.
  2. Cut a piece of string about iv″ – v″ longer than your radius. We used a 10″ length of cord.
  3. Tie one end of the string to a brusk pencil.
  4. Place the point of the pencil toward the outer edge of the paper with plenty room from the edge to make a full sweep.
  5. Measure from where the bespeak of the pencil touches the paper backwards by the length of the radius (in this case half dozen½").
  6. Pin straight through the string into the paper at that verbal bespeak.
  7. Keeping the cord taut, draw a perfect circumvolve using your bootleg compass.

The folded quarters method

  1. Again, outset with a square of lightweight paper at least 1″ larger than the circle you want to depict.
  2. Fold the newspaper into quarters. Make sure your original square is even and true! Position the newspaper 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 exact centre of the lesser left corner of your folded square. Swing the ruler from the pinnacle to the lesser of the square, like a pendulum or compass, measuring and marking a dot at the six½" point in three to four spots. You are creating a semi-circle arc. Make certain the end of the ruler at the corner point doesn't shift position.
  4. Cutting along the arc through all the layers and unfold the finished xiii″ circle. You can now use this paper blueprint to cutting your fabric circle.

With your spiffy new circle, you can now sew the side seam in the master textile cut. Then pin the base to the resulting tube and sew together the tube to the circle using a ½" seam allowance. The result is a 12″ diameter finished base.

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