The circumvolve is, in my humble opinion, the Queen of the geometric shapes. Don't go me wrong; I similar all those squares, rectangles, triangles, octagons, and whatnot; just the circle is the coolest of the agglomeration: smooth and pretty and endlessly useful. Even so, trying to draw a perfect circle without a pattern is a challenge, and figuring out the proper size of an opening into which a circumvolve can be inserted requires working with Pi (or π), which is not the delicious kind y'all can eat with a bit of ice foam. We're here today to assistance you with the steps you lot've forgotten since loftier schoolhouse geometry class (or maybe never learned because yous were also busy passing notes with Susan Ellery!). We'll show y'all the parts of a circle, how wide to cutting fabric to fit a circle, and how to draw a circle without a pattern. We've also included a handy conversion from decimals to inches, which is necessary when working with Pi.

The parts of a circle

Permit's get-go 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 circumvolve to the outside edge

Diameter: the distance across a circle through its eye point

Circumference: the distance around the outer edge of a circumvolve

π or Pi: the name given to the ratio of a circle'due south circumference to its diameter, expressed as the decimal three.xiv

How broad to cut fabric 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 make a tube. That width is the circumference of the circumvolve that will be inserted into the tube (nosotros have a bully step-by-step tutorial on how to insert a circle into a tube).

The formula: 3.14 (π) x diameter = circumference

Case: You want 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 as well: 3.14 x xxx cm = 94.2 cm)

An important stride many people miss at this point is forgetting to add together extra (to both pieces) for the seam assart. If y'all use a standard ½" seam allowance, you need to add together ane″ to the bore of your circle ( the bore increases by double the seam allowance)and i″ to the width of your fabric (½" for both sides of the seam allowance). In our example, that means:

The circle should beginning equally 13″ in diameter.

The fabric should exist 38.68″ in width

The height of your fabric cut is variable and dependent on your project. For example, a tall duffle bag might exist xxx″ in height whereas a shorter bucket might be only x″.

Converting a Decimal to a US Ruler Measurement

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

For those of us in the world of inches, you lot demand to detect a yardage conversion.

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

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

How to Draw a Circle

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

To first, you demand to know how big you want your circle (the diameter). For our ongoing example, nosotros want a xiii″ diameter circumvolve

To draw a circle you lot need to know its radius. As you learned in a higher place in the first section, the radius is one one-half of the diameter. In our case, 1 half of thirteen″ is vi½".

The total circle method

  1. Use a sheet of lightweight newspaper (graph or pattern newspaper works well) that is at to the lowest degree 1″ larger all effectually than the circumvolve you want to draw.
  2. Cut a piece of string about four″ – 5″ longer than your radius. We used a 10″ length of cord.
  3. Tie one end of the string to a short pencil.
  4. Identify the bespeak of the pencil toward the outer edge of the paper with enough room from the edge to make a full sweep.
  5. Measure out from where the signal of the pencil touches the paper backwards by the length of the radius (in this case 6½").
  6. Pin straight through the string into the paper at that exact point.
  7. Keeping the string taut, draw a perfect circle using your bootleg compass.

The folded quarters method

  1. Again, first with a foursquare of lightweight paper at least 1″ larger than the circle you want to depict.
  2. Fold the paper into quarters. Make sure your original foursquare is fifty-fifty and true! Position the newspaper with its folded edges along the lesser and left side and the open edges along the top and correct side.
  3. Place a see-through ruler at the exact heart of the bottom left corner of your folded square. Swing the ruler from the top to the lesser of the square, like a pendulum or compass, measuring and marker a dot at the 6½" point in 3 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. You can now utilize this paper pattern to cutting your textile circle.

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

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