Women's One Piece Block

Absolutely Everything Starts Here

Note: This technique suits bust sizes between 80cm and 94cm only. Larger sizes will be covered separately


The process for drafting the Women’s One Piece Block is fairly straight forward if handled in bite size steps. Using either a CAD package or drafting paper, simply follow the drafting instructions. At the end of each step your drawing should match the illustration. If it doesn't go back to the start of that step and work your way through again. This example block has been drafted for a size 10B/C using 12% horizontal negative ease and 0% vertical ease. Of course, you can substitute my values for your own measurements. The way to write this on the block is '88/100' meaning the block is 88% of the natural horizontal and 100% of the natural vertical. This is usually referred to by industry as the reduction ratio. I still prefer to call it negative ease as opposed to reduction, because sometimes you may have both positive and negative ease in the same garment … it’s up to you!

Step One

1-2: Square down nape to waist measurement. Square across the page from points 1 and 2.
2-3: Square down waist to crotch. Square across the page from 3.
1-4: Square down 2cm to point 4. Square across the page from 4.
3-5: Square down half gusset measurement to point 5. Square across 7cm to point 6 +/- 3mm per size from size 10.
3-7: 1/4 natural hip. Square up to point 8. The hip measurement is not reduced by 12% as the swimsuit does not wrap around the leg.
3-9: 1/8th natural hip plus 1cm.
2-10: 1/4 waist measurement x 0.88 (reduction of 12%). Join point 7 to point 10. Mark point 11 halfway along this line. Create a curve to connect points 6 to 9 and 11.

Step Two

7-12: 1/4 natural hip (same as 3-7). Square up to points 13 and 14.
12-15: Square across 3.5cm from point 12 to 15 +/- 1.7mm per size from size 10.
12-16: Square down 9.5cm from point 12 to 16. +/- 3.5mm per size from size 10
16-17: Square across 7cm from point 16 to 17 +/- 3mm per size from size 10.
14-18: 1/4 waist measurement x 0.88 (reduction of 12%). Join point 7 to point 18. Mark point 19 halfway along this line.
19-20: Square across from point 19. Mark point 20 at 1/3rd along this line. Create a curve to connect Points 17, 15, 20 and 19. Once the block is cut out, the leg curves can be trued up. Leg curves are purely a style choice and can be moved once you know what you’re doing.

Step Three

13-21: 1/4 bust x 0.88 + 1.5cm. Square down to waist line. The 1.5cm is added to the front block and removed from the back block to move the side seam more toward its natural position. If you are designing for a larger cup size on the block you may want to move the side seam back a little more. 1.5cm is about right for a 10B/C.
1-22: 1/4 bust x 0.88 - 1.5cm. Square down to waist line.
14-23: Waist to bust. Square across from point 23 to point 24. Join point 18 to point 24.
23-BP: ½ Bust separation x 0.88. Draw a line from Bust Point to point 25 which is square to line 18-24. This is the bust dart position.
24-26: Mark point 26 3cm up from point 24. Square across block and mark in point 27. Join point 10 to point 27.

Step Four

13-28: 1/6th neck measurement.
13-29: 1/6th neck measurement. Draw in front neck curve. Joint point 29 to BP.
1-32: 1/6th neck measurement. Draw in back neck curve. Draw a line shoulder width x 0.88 to meet the line squared across from point 4. Mark the intersection as point 33. Draw down a line square to line 32-33 from point 33.
29-30: Draw a line shoulder width x 0.88 to meet a line squared across from point 33. Mark the intersection as Point 30. Trace the line shown in red onto a new sheet of paper.
29-31: Draw in point 31 the Dart Width from point 29.

Step Five

Rotate the traced section as shown. Draw down a line square to line 31-30 from point 30. Draw in armhole curves as shown. The armholes curves can be trued up after the block is cut out. Draw in side seams as smooth curves.

Step Six

Rotate the front shoulder section shown in red back to the neckline so as to re-open the bust dart at the side seam. The rotation should be centred on the bust point. Mark in the bust line position on the back block by measuring up from the waist line, along the side seam to the bottom of the bust dart. If you're wondering why the front and back armholes have ended up a different length take a look at the section on Making the Sleeve Block.

Step Seven

Remove unnecessary guidelines, points and numbers. If you drafted the block on paper, cut out or retrace the front and back blocks and true up all curves. Make sure you clearly label your block with a title, panel name, size, date, author’s name and version number. Do not add seam allowance to the block! 

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