2.1 Block for stretch fabrics (horizontal and vertical reductions)

To calculate negative ease, you need the fabric you’ll be using (and a buddy helping you measure it):

1. identify a 20x20cm square on fabric (draw a square with chalk or pins with sides 20cm long – it should not be on the selvedge or on the cut edge)
2. see those little V on fabric? Keep them vertical and pull across them – so, pull in the crossgrain direction until you like the amount fabric stretches (this depends a lot on fabric and on your how tight you like garments to fit)
3. keep pulling and ask your buddy to measure the new square width
   e.g. 20cm became 28cm
   calculate 20/24 to get the coefficient k = how much you need to reduce horizontal measurements
   k = 20/28 = 0.7
4. then calculate the coefficient y for vertical reduction as well
   e.g. 20cm became 26cm
   calculate 20/26 to get the coefficient y = how much you need to reduce vertical measurements
   y = 20/26 = 0.77

Check here a video on how to measure this reduction. Grab a piece of 4-ways stretch fabric and start experimenting!

Draw a line on left part of your sheet: this is center back. At its upper part draw a perpendicular to the line, and mark the point where the two lines meet as a. Then, on center back line, find the following points:

a-w is back waist length multiplied by coefficient y
w-h is hip level multiplied by coefficient y
w-n is crotch level *y, crotch depth or level is the difference from the measurement waist to ground minus inseam (crotch to ground) 
n-f is (hip circumference/20 + 1.2cm) *y.

—> I use the symbol * instead of ‘multiplied by’

Square out towards the right from all of these points. This way you find waist line, hip line and crotch line.

a-b = 1/2 bust circumference *k
Square down from point b and draw a line parallel to center back. This line is center front.

Extend the perpendicular lines coming from w, h and n points and find the matching points w1, h1 and n1 on center front line.

Then find armhole level
a-c (armhole depth) = [(bust circumference/6) +8cm]*y

Square out from c until you meet center front and name the point c1.

Mark the midpoint between c and c1 as c4, and square down through all lines to find w2, h2, n2, f2.

For drawing shoulder and upper back area, draw

a-a1 = 1/2 across back (meas. n.15) *k
drop a perpendicular from a1 to find c2 on chest line
a-a2 = (chest circ/12) *k
a-a3 = difference between side back waist length and center back waist length

To find shoulder line and shoulder point a4 you have to draw two arches as follows, and mark their intersection:

• first arc is obtained by pointing on a2 and using as radius the shoulder top measurement (meas. n.14) *k. Draw a big arch towards right
• second arc is obtained by pointing on w and using back shoulder slope *y as radius (meas. n. 12). Draw an arc in direction to a1.

Where the two arches intersect, mark point a4. This is shoulder point.

Join a2 to a4 and draw shoulder line.

Divide segment a5-c2 in half and mark it as a6.
Draw the armhole a4-a6-c4.

w-w3 = (waist circ/4) *k + 2 to 3cm for dart, if needed for the style – not shown here

h-h3 = (hip circ/4) *k

f-f1 = 3 to 5cm (crotch width)
f-f2 = raise by 2cm and join to f1 with a curve

n-n3 = (hip circ/8) *k

Draw side seam c4-w3-h3, then draw leg opening h3-n3-f1.

Now let’s move to front.

First, measure from b towards the left
b-b1 = (front width/2) *k

Then, starting from point w1 measure upwards
w-b1′ = front waist length *y

To draw front neckline you need
b1′-b2 (on front) = a-a2 (on back)
b1′-b3 = (b1′-b2) +1cm

Draw the curve connecting b2 and b3.

Then draw bust position:
b1′-c5 = bust height *y
c5-c6 = 1/2 breast span *k

c5 point might sit above, below or exactly on top of c-c1 line: the position depends on vertical ease at armhole and personal measurements.
c6 point represents breast center, labeled as C in the lesson on how to take measurements, and it’s the reference point for darts and dart manipulation (we deepened this topic in lessons 6-7 of module 1).

Join points b2 to c6 with a straight line. This is first leg of the dart.
Calculate the measurements [(breast span/2) -1,5cm] *y and find point c7 along b2-c6 line, measuring upwards from c6. This point represents chest level.

To draw dart depth at chest level you need to calculate half of the difference between bust circ and chest circ
c7-c8 = [(bust circ – chest circ)/2] *k

Draw the second leg of the dart as a segment that starts from c6, passes through c8 and measures as much as c6-b2. Label c9 the point you find.

So dart legs are b2-c6 and c9-c6.

To find shoulder line on front, you should draw two arches as done on back and mark the point where they intersect:

• first measure the shoulder line on back as a2-a4, then use it as radius to draw an arc whose center is c9
• then, draw another arc starting from point c6 using front shoulder slope

Where arches meet mark the point b5. Join points c9 to b5 with a straight line: this is front shoulder line.

To draw front armhole we need to find some further reference points:

• starting from point c3 along line c3-b1 move upwards as [(c2-c3)/3]+1cm and mark the point as b6
• draw the line b6-b7 = c7-c8; this amount matches the volume lost with dart depth

To draw front armhole connect points b5-b7-c4 with a soft curve.

w-w4 = (waist circ/4) *k + 2 to 3cm for dart, if needed for the style – not shown here

h-h3 = (hip circ/4) *k

n1-o = (hip circ/10) *y
o-o1 = (n1-o)/2

o-o2 = as f-f1 on back = 3 to 5cm (crotch width)
o2-o3 = raise by 1cm, then join o3 to o with a curve

h1-h5 = hip circ/20 *k
find point h6 halfway between h4 and h5, then raise by 1 to 1.5cm to find point h7 (needed for drawing a soft curve for leg opening)

n1-n3 = (h1-h5) -2cm
o1-o4 = (h1-h5) -1.5cm

n-n3 = (hip circ/8) *k

Draw side seam c4-w4-h4, then draw leg opening o3-o4-n3-h5-h7-h4.

Trace a copy of back and front without construction lines, then smoothen side seam line and true the pattern by joining pieces in a temporary way:

• first at shoulder to check top armhole and neckline shapes
• then at side seam to check bottom armhole and leg opening shapes
• lastly at crotch to check crotch/leg opening shape.

Depending on what this basic pattern will be, you can change crotch line as shown in the image:

• option 1, as the construction. Back is shorter, front is longer: this is needed for all briefs, swimsuit…pieces without bottom opening. Then longer front ensures the seam to sit in a comfortable position
• option 2. If you want to make an underwear bodysuit with bottom opening (snaps, hook&eye..), then we recommend to merge part of the front (the part from o to n1) to back piece, so that front is shorter and back longer, and the closure is more comfortable.