The circumvolve is, in my apprehensive opinion, the Queen of the geometric shapes. Don't go me incorrect; I like all those squares, rectangles, triangles, octagons, and whatnot; simply the circumvolve is the coolest of the bunch: shine and pretty and endlessly useful. However, trying to draw a perfect circumvolve without a pattern is a claiming, 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 you lot tin can eat with a chip of ice foam. We're here today to help you with the steps you've forgotten since high school geometry grade (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 circumvolve, and how to describe a circumvolve 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 circumvolve

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

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

Diameter: the distance across a circumvolve through its center betoken

Circumference: the distance effectually the outer edge of a circumvolve

π or Pi: the proper name given to the ratio of a circle'due south circumference to its bore, expressed as the decimal 3.14

How wide to cut fabric to fit a circle

If y'all know the bore of your circle, you tin utilise a standard formula to figure out the width of the fabric cutting needed to brand a tube. That width is the circumference of the circle that will be inserted into the tube (nosotros have a corking stride-by-step tutorial on how to insert a circle into a tube).

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

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

iii.14 x 12 inches = 37.68 inches

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

An important footstep many people miss at this point is forgetting to add extra (to both pieces) for the seam assart. If yous use a standard ½" seam assart, y'all need to add ane″ to the diameter of your circumvolve ( the diameter increases past double the seam assart)and 1″ to the width of your textile (½" for both sides of the seam allowance). In our case, that ways:

The circle should showtime as 13″ in diameter.

The fabric should be 38.68″ in width

The pinnacle of your fabric cut is variable and dependent on your project. For example, a tall duffle bag might exist thirty″ in height whereas a shorter bucket might exist only 10″.

Converting a Decimal to a The states Ruler Measurement

If you 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, yous demand to discover a yardage conversion.

In our example nosotros 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". We can use 38⅝" every bit the width of the textile piece yous are cut for your tube.

How to Draw a Circle

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

To start, yous need to know how large you lot want your circle (the diameter). For our ongoing example, we want a 13″ diameter circle

To depict a circumvolve yous demand to know its radius. Equally you lot learned above in the first department, the radius is one half of the diameter. In our example, 1 half of thirteen″ is half dozen½".

The full circle method

  1. Use a sheet of lightweight paper (graph or pattern paper works well) that is at least one″ larger all effectually than the circle yous want to draw.
  2. Cut a slice of cord about 4″ – 5″ longer than your radius. We used a 10″ length of string.
  3. Tie i finish of the string to a brusk pencil.
  4. Identify the bespeak of the pencil toward the outer edge of the newspaper with enough room from the edge to brand a full sweep.
  5. Mensurate from where the point of the pencil touches the paper backwards past the length of the radius (in this case 6½").
  6. Pivot directly through the string into the paper at that exact betoken.
  7. Keeping the cord taut, draw a perfect circle using your homemade compass.

The folded quarters method

  1. Again, start with a square of lightweight newspaper at least 1″ larger than the circle you want to draw.
  2. Fold the paper into quarters. Brand certain your original square is fifty-fifty and true! Position the newspaper with its folded edges along the bottom and left side and the open up edges along the top and right side.
  3. Place a see-through ruler at the exact heart of the bottom left corner of your folded foursquare. Swing the ruler from the top to the bottom of the foursquare, like a pendulum or compass, measuring and marking a dot at the 6½" point in three to iv spots. You are creating a semi-circumvolve arc. Make sure the end of the ruler at the corner indicate doesn't shift position.
  4. Cut forth the arc through all the layers and unfold the finished xiii″ circle. Yous tin now use this newspaper design to cutting your fabric circle.

With your spiffy new circle, 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 circumvolve using a ½" seam allowance. The consequence is a 12″ diameter finished base.

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