The circle 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 circle is the coolest of the bunch: smooth and pretty and endlessly useful. Notwithstanding, 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 can be inserted requires working with Pi (or π), which is not the delicious kind you can eat with a flake of ice cream. Nosotros're here today to help you with the steps you've forgotten since high schoolhouse geometry form (or peradventure never learned because you were too busy passing notes with Susan Ellery!). We'll bear witness you lot the parts of a circle, how wide to cutting fabric to fit a circle, and how to draw a circle without a blueprint. We've also included a handy conversion from decimals to inches, which is necessary when working with Pi.

The parts of a circle

Allow's kickoff 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 circle to the exterior edge

Diameter: the altitude beyond a circle through its center point

Circumference: the distance effectually the outer edge of a circle

π or Pi: the proper name given to the ratio of a circle's circumference to its diameter, expressed every bit the decimal 3.14

How broad to cut fabric to fit a circle

If you know the bore of your circle, yous tin 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 circle that will be inserted into the tube (we take a cracking step-by-pace tutorial on how to insert a circle into a tube).

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

Example: You want a finished 12″ diameter base of operations (a 12″ bore circle) in a duffle purse.

3.14 x 12 inches = 37.68 inches

(This works with the metric system likewise: iii.14 ten 30 cm = 94.two cm)

An important step 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 need to add together 1″ to the diameter of your circle ( the diameter increases by double the seam allowance)and 1″ to the width of your cloth (½" for both sides of the seam assart). In our example, that ways:

The circle should showtime equally 13″ in diameter.

The cloth should exist 38.68″ in width

The height of your material cutting is variable and dependent on your project. For example, a tall duffle bag might be thirty″ in height whereas a shorter saucepan might be but 10″.

Converting a Decimal to a United states Ruler Measurement

If you are using Pi, retrieve it ever returns a decimal number. If you already bargain with the metric arrangement, you rock –  no conversion necessary.

For those of us in the earth of inches, you need to observe a yardage conversion.

In our case we accept 38.68 inches. Harumph! The table below will give y'all a close-plenty ruler friction match.

The decimal .68 is closest to .63 or ⅝". We can use 38⅝" as the width of the textile piece y'all are cut for your tube.

How to Depict a Circle

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

To commencement, you lot need to know how large y'all want your circle (the diameter). For our ongoing example, nosotros desire a 13″ diameter circle

To depict a circle you need to know its radius. Every bit you learned above in the first section, the radius is one half of the diameter. In our example, 1 one-half of thirteen″ is 6½".

The total circle method

  1. Apply a sheet of lightweight paper (graph or pattern paper works well) that is at to the lowest degree 1″ larger all effectually than the circle you want to draw.
  2. Cutting a slice of string almost iv″ – 5″ longer than your radius. We used a x″ length of cord.
  3. Tie one end of the string to a short pencil.
  4. Identify the indicate of the pencil toward the outer border of the paper with plenty room from the edge to make a total sweep.
  5. Measure out from where the betoken of the pencil touches the paper backwards by the length of the radius (in this instance 6½").
  6. Pin straight through the string into the paper at that verbal point.
  7. Keeping the string taut, draw a perfect circle using your homemade compass.

The folded quarters method

  1. Again, commencement with a square of lightweight paper at least 1″ larger than the circle you lot desire to describe.
  2. Fold the paper into quarters. Make certain your original square is even and true! Position the paper with its folded edges forth the bottom and left side and the open edges along the top and right side.
  3. Place a meet-through ruler at the exact centre of the bottom left corner of your folded foursquare. Swing the ruler from the top to the bottom of the square, like a pendulum or compass, measuring and marker a dot at the 6½" betoken in iii to four spots. You are creating a semi-circumvolve arc. Brand certain the cease of the ruler at the corner point doesn't shift position.
  4. Cut along the arc through all the layers and unfold the finished thirteen″ circumvolve. You can now utilise this newspaper pattern to cut your textile circle.

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

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