How to Use an L-Square for Tailoring

Written by mercedes valladares
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One of the most indispensable tools used in pattern making is the tailor's square, referred to as the L-square. This pattern-drafting ruler has an L shape, generally measuring 14 inches by 24 inches. The ruler has a vertical long arm and horizontal short arm intersecting at one angle. Patternmakers use the measurement scales for grading patterns, which refers to increasing or decreasing size ranges. The long arm divides into 6ths and 12ths and the short arm in 8ths and 16ths. Use this invaluable tool to make half-scale patterns from your existing patterns.

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Things you need

  • Pattern paper
  • Drafting pencil
  • L-square ruler

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  1. 1

    Trace your existing pattern on pattern paper with a drafting pencil. Keep the original pattern for reference.

  2. 2

    Refer to the calibrated side measurements. The L-square has a built-in calibrated measurement system reducing the existing measurement to the half-scale. Certain L-square brands have the long arm calibrated into 24ths and the short arm into 32nds on one side and the reverse side is calibrated into 8ths. Choose the side of the ruler for half-scales.

  3. 3

    Position the L-square ruler along the vertical line of your pattern. For instance, if you are making the half scale for a side seam, align the long arm vertically on a 90-degree angle, along the side seam line.

  4. 4

    Position the angle where the long and short arm meets, referred to as the zero point, at the bottom of the seam line.

  5. 5

    Draw a line from the zero point to the desired measurement along the long arm. For example, if your measurement is 16 inches, draw the vertical line to the 16 measurement marking on the long arm. This produces a perfect 8-inch seam for the half-scale pattern.

  6. 6

    Repeat Steps 3-5 to alter the remaining vertical and horizontal seam lines of the pattern into half scales.

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