One of the most important tools you will need is a “Flexible Ruler” to measure curved seams. Using a tape measure will not be accurate for bra making.

If you cannot get hold of a flexible ruler you can make one by photocopying a normal ruler (a ruler with black markings on white plastic works best) onto an clear acetate plastic sheet (make sure the acetate plastic sheet is the right type for a photocopier) and then cut out the ruler image.

“Flexi Curve” for drawing smooth free curves and for taking a “breast root trace”, and a set of “French Curves”

Taking a breast root trace using a Flexi curve (right)

If you have one or have access to one, a Technical Drawing Board, consisting of around an A2 (42 x 59cm or 16.5 x 23.4 in) size board, “T” Square, 45^o Set Square and 30^o/60^o Set Square.

Drawing parallel lines or lines at right angles to each other is so much quicker with a drawing board. But you can do all the drafting/drawing without one.

Pencils and sharpener. I was always told at university to use a mechanical “Clicky” Pencil but you can draw much finer lines with a properly sharpened ordinary pencil.

Spring Bow Compasses, one large and one small. (These are usually sold in a handy box set)

Metric Ruler.

Tracing wheel and Carbon Paper.

A3 size paper (lots of it - that's approx size 30x42cm or 12x17 in)

Step One

On a sheet of A3 paper in landscape, draw a horizontal straight line 12.85cm long near to the bottom edge of the paper.

With your compasses set at 8.72cm, draw an arc from one end of the line and another intersecting arc from the other end of the line.

Join up the points with straight lines, as in the diagram.

This will form the “Dart” of the cup. You can write “Point of Bust” or “PB” next to the intersection of the arcs.

Step Two

From the left end of the 12.85cm base line, set your compass to 9.4cm and draw an arc.

From the “Point of Bust”, set your compass to 10.26cm and draw an intersecting arc to the first arc.

From the right end of the 12.85cm base line, set your compass to 9.4cm and draw an arc.

From the “Point of Bust”, set your compass to 9.24cm and draw an intersecting arc to the first arc. Join up the points with straight lines, as in the diagram.

Step Three

Still using your compasses, draw arcs from the 12.85cm base line at 11.5cm and 10.45cm from Point of Bust on left (Underarm) side and 10.8cm and 9.25cm on right (Centre front) side.

Join up with lines from base line and point of bust.

Step Four

Next, to mark the “Cup Apex” (the point were the bra strap joins to the cup).

From point of bust, arc out a line 11.57cm, an arc 13.6cm (this line will become the “Neck Line Hem” of the bra cup) and an arc 7.13cm (this line will be curved to become the “underarm” hem of the cup) See diagram for start points of the arcs / lines.

Later this cup apex point can be moved to suit individual fit / styles.

Step Five

In woodwork we measure twice and cut once, so check the cup measurements.

You should now be ready to draw the curved lines (red lines in diagram) of the cup outline using a Flexi Curve or French Curve.

Try to make the curves smooth and flowing through the points.

Step Six

Next, extend the lines that “radiate” from the Point of Bust point to the edge of the cup and beyond, number the lines 1 to 7 clockwise starting at the “cup apex” as in the diagram.

We will use these lines to “Shift Grade” the cup to your size.

Lines 3 and 6 are very important. When you tape together a test paper bra cup, lines 3 and 6 should form a straight, horizontal line over the fullest part of your breast (we will not put the lines on the fabric! The lines will only be on the paper block/pattern). When we come to adapting the cup block for other styles we will use lines 3 and 6 to split the cup into panels.

CUP SIZE

GradingTable

OVER BREAST MEASUREMENT

(All Measurements in cm) grading step = 1.7cm

Grading Example: - Size 4 to Size 8 cup

Now use the cut out copy of the size 4 cup as a template to draw each “corner” of the new “your” size cup.

Align the size 4 cup to the lines and grade marks on your original draft and draw in the corner. Do not completely draw around the cup at each step, just draw the corner.

You can see this process in the diagrams below.

Now using your Flexi Curve / French Curve, smoothly join up the “corners” to give you the new cup outline.

Breast Root Trace

To take a breast root trace, use a Flexi Curve and a sheet of paper.

Put the Flexi Curve around your breast (right breast as we are drafting the right half of the bra or you can trace your left breast and flip the trace over on the paper) and make sure it is up against the point around where your breast tissue joins the chest wall. This is the same point around the breast where the underwire of a correctly fitting bra should sit, not on breast tissue (pain) and not away from the breast (poor fit).

Now mark on the Flexi curve, with chalk or thin tape, the point directly (vertically) below the nipple or fullest part of the breast.

Next, imagine a horizontal line across the fullest part of the breast and put two marks on the Flexi Curve ether side of the breast and about 2cm above the imaginary horizontal line.

You may need the help of a close friend to do this while you hold the Flexi curve against yourself.

Now CAREFULLY take the Flexi Curve away from your breast without moving its curve and place it on the sheet of paper. Again carefully draw around the edge of the flexi curve that was up against your breast and transfer the three marks to the curve on the paper.

You now have a curve to help you find the correct underwires for your size and to draft the correct cup to cradle seam. Hurrah!! You just may be on the way to a bra that actually fits you.

Now you need to get hold of two underwires for your bra that match your breast root trace. If you are obtaining your wires in person from a shop you can take your breast root trace with you and try their wires against it. If you are planning to get your wires from the internet see if the company has “to size” drawings or pictures of the wires they sell, so you can again match up your trace to the correct wires.

An Internet company I use for corset and bra bits is www.sewingchest.co.uk; they have a downloadable PDF document that shows all the underwire sizes that they sell. You could try to find “MS20” underwires in your size, the MS20 underwire is a good “day bra” shape and it is the wire shape that the largest UK underwear retailer (clue: give us an "M"; give us an "S") have as their standard.

One major point: the wire that is closest to the size and shape of your breast root trace will veer away from the trace curve at the underarm side (right).

This is because when the wires are in the bra and worn, the wires are “pulled open” or “Sprung” to the curve of your breasts by the elastic pull of the wings of the bra.

So do not worry if you cannot find underwires that exactly match the curve of your trace.

Another tip: choose a “Day wear” underwire. Steer clear of “Plunge” underwires and “Strapless” styles at this stage.

Here is the shape of a typical Daywear wire for a UK 34”B bra which will work with the Size 4 cup, for readers who do not have “client” to make a bra for. Print the picture off and use it to obtain two underwires.

When you have got your wires, you can continue with the pattern drafting, or you can use your Breast root trace if you want to have a go at making the bra without any underwires.

Step One

Finding the “balance point” of your underwire.

On a sheet of A3 paper in landscape mode, draw a horizontal line across the centre of the paper. Near to the right hand side of the paper draw a line at 90 degrees (vertically) to the first line.

Place one of your underwires on the two lines so that the inner edge of the centre front end of the wire touches the vertical line and the bottom of the wires curve (again inner edge) touches the horizontal line as in the diagram.

Now where the wire touches the horizontal line, put a mark on the paper. This is called the “Balance Point” of the wire. Next, lightly draw around the inner edge of the wire onto the paper and mark the end points of the wire.

On the paper, measure down 5mm from the centre front end of the wire's curved line and mark the point.

Place the wire back on the paper on its curve and then shift the wire around the curve so that the wire's CF end now aligns with the 5mm point on the paper.

Again, draw around the inner edge of the wire onto the paper and mark the end points of the wire.

This slight “tilting” of the wire helps for a better fit against the curvature of the chest wall.

Step Two

Now you need to “spring” the wire and redraw its curve. You may need the help of a friend to draw the sprung wire curve whilst you hold the wire open.

On the paper, at the underarm end of the wire curve, place a mark 1.5cm horizontally to the left of the wire curve. Now whilst holding the underwire on the paper so that the CF (centre front) end of the wire stays in position against the first vertical line / curve, pull open the underarm end of the wire to the 1.5cm mark and redraw the wire's curve.

Without an Underwire

For those of you who do not want to use underwires, copy your breast root trace onto a sheet of thin card and cut the card along the line of the trace. You can now use your trace as an underwire template. DO NOT try to “spring” your trace, as it is already the correct curve for your bra!

As with the wire drawing, place your trace template against the horizontal and vertical lines and do the 5mm “tilt” using the centre front mark you placed on the trace as the “CF end of the wire” and draw around the curve. Remember to copy the three marks (centre front, under bust and underarm side) on the trace on to the paper. Please remember that with the larger size cups, using the correct size underwires helps the shaping and support of the breasts.

Step Three

After you have drawn the curve of the wire in the “sprung” position, you need to add to each end of the curve 5mm for “Wire play” and 3mm for “Bar tack sinkage”. So that will be 8mm added to each end of the underwire curve. Extend the curve.

Step Four

Marking in the centre front line of the bra:

From the CF top point of the wire curve, draw a horizontal line 1.2cm long then draw down a vertical line at the end of this line. This is the CF (centre front) line of the bra.

Step Five

As the underwires will be in “wire casing” you need to add 3mm allowance to the inner edge of the wire curve.

This is not “seam allowance” - we will add that at the end.

Now that we have drafted the curve and length of the “cup to cradle seam” for the cradle, we need to transfer the length of the curve to the cup.

As the “Balance Point” marked on the paper is also the alignment mark for the “cup dart”, we must measure from this point up either edge of the cup and adjust the cup.

Use your “Flexible Ruler” to accurately measure Length “A” and Length “B” and transfer the lengths to the cup.

You may need to shorten or lengthen the cup curves to match the cradle curves and then redraw the Neckline hem and the underarm hem.

Step Seven

We will now draft the rest of the cradle and wing. Remember, we are drafting just one half of the bra (right side).

Measure down from the first horizontal line you put on the paper and mark four lines, at 6mm, 18mm, 28mm and 76mm respectively, horizontally across the paper.

Step Eight

From the top of the cradle / wire seam at CF, draw a horizontal line across the cradle to the underarm side.

Where this line intersects the underwire curve line, draw a line vertically down to the “28mm” line and mark the crossing point “A”.

Step Nine

Now for some Maths. If you have been following Cathy Hay’s Corset drafting article you may already understand how to calculate a measurement using a Percentage.

You will use your “Back Measurement”, taken from side breast root, around your back, horizontally to your other side breast root.

For example:

If I asked you to draw a line 32% of your back measurement the calculation would be:

Back measurement = 50cm,

Divide 50cm by 100 = 0.5,

Then multiply 0.5 by 32 = 16cm

So the length of your line would be 16cm.

Again if I asked you to draw a line 17.1% of your back measurement the calculation would be:

Back measurement = 50cm

Divide 50cm by 100 = 0.5

Then multiply 0.5 by 17.1 = 8.55cm

So the length of your line would be 8.55cm.

We will now draw in the Cradle to Wing side seam.

From point A on the 28mm line, measure alone the line 4.56% of your back measurement (BM) and place a mark.

Example, BM = 50cm, 50 / 100 = 0.5, 0.5 x 4.56 = 2.28cm

Follow the diagram to put in the other lines. From the new point on 28mm line, draw a line 17.1% BM (back measurement). From top of wire curve at underarm, 9.3% BM to intersect 17.1% line. This 17.1% line will be the Cradle Side Seam.

Step Ten

From the bottom of the 17.1% cradle seam line draw a line 32% BM long so that it intersects the 76mm horizontal line.

At this intersection point draw a line 2.5cm long at right angles to 32%BM line. This 2.5cm line will be the CB (Centre Back) of the bra and the point to sew on the hook & eye tape. 2.5cm should be wide enough for a two hook & eye wide fastening, although for the larger cup sizes you may need to go for a three hook & eye wide fastening. You can change this measurement when you have obtained your hook & eye tapes.

On the 32% line, put a mark 4.8cm from the 2.5cm hook & eye line then at right angles to the 32% line draw a line 6.6cm up from the line.

Step Eleven

Now that we have the main points of the cradle and wing marked out, we can join up the points with smooth curves.

Using your Flexi Curve or French Curves, draw the “underband hem”. Start on the 6mm line at right angles to the CF line, then take the curve through the 18mm line below the “Balance Point”, continue on through the 28mm line /side seam line intersection, curve up slightly above the 32% line and end at the bottom of the 2.5cm line.

For the “strap platform”, a simple curve from the top of the 2.5cm line to the top of the 6.6cm line. For the  “Underarm hem” start at the top of the 6.6cm line, go through the top of the side seam line and finish at the top of the cradle to cup seam line/curve.