Chapter 11

Trousers

Drawn for size Every number below follows the size you pick.

Trousers are a skirt split into two legs. The new part is the crotch: a curve that goes under the body and joins the legs.

You draw the front leg first: the waist, the seat line and the crotch line from the body rise, the fork that reaches between the legs, and the crease line down the middle of the leg, which is also the grain line. The back is drawn over the front, with a longer fork and a raised centre back for the seat.

What you need

Measurement	Where the tape goes	Size 50
Waist	Round the natural waist, where the body is narrowest, usually just above the navel.	88.0 cm
Seat	Round the fullest part of the seat, feet together.	102.0 cm
Outside leg	Down the side of the leg from the waist to the floor, without shoes.	105.5 cm
Body rise	Seated on a firm, flat chair: from the waist at the side straight down to the seat of the chair.	27.0 cm

Drafting, step by step

Each picture shows everything drawn so far; the new line of the step is in colour. The formulas show the names of the measurements first, then the numbers for size 50.

Front
Step 1
Side line
start at the waist
Trousers are drafted from the side: this vertical line is the outside of the leg, with the waist at the top. All the depths are measured down it.
Step 1–2
Crotch depth
Body rise + crotch depth ease
= 27.0 + 1.0 = 28.0 cm
Body rise is measured sitting, from the waist down to the chair. The ease adds a little so the seam does not cut in when you sit or bend.
Step 1–3
Seat line
(Body rise + crotch depth ease) × 0.68
= (27.0 + 1.0) × 0.68 = 19.0 cm
The seat is fullest about two thirds of the way down the rise, so the seat width is set out on this line.
Step 1–4
Trouser length
Outside leg − waistband height
= 105.5 − 4.0 = 101.5 cm
Outside leg is measured from the waist to the floor; the waistband sits on top of the trousers, so its height is taken off here.
Step 2–5
Knee line
crotch depth + (length − crotch depth) ÷ 2 − 4
= 28.0 + (101.5 − 28.0) ÷ 2 − 4 = 60.8 cm
The knee sits a little above halfway down the leg. The leg is shaped at this line, so it is placed before the widths.
Step 3–6
Front seat width
Seat ÷ 4 − 1 + seat ease ÷ 4
= 102.0 ÷ 4 − 1 + 6.0 ÷ 4 = 26.0 cm
Each front takes a quarter of the seat less 1 cm and the back gets 1 cm more, because the body is fuller behind. The centre front line goes up from here to the waist.
Step 6–7
Front fork
Seat ÷ 16 + 0.5
= 102.0 ÷ 16 + 0.5 = 6.9 cm
The fork carries the crotch seam between the legs. It is short at the front and much longer at the back, which has to wrap under the seat.
Step 8
Crease line
(seat width + fork) ÷ 2 − 0.5
= (26.0 + 6.9) ÷ 2 − 0.5 = 15.9 cm
The crease splits the leg in half at the crotch line. The knee and hem widths are set out equally either side of it so the leg hangs straight with the crease in the middle.
Step 9–12
Knee and hem widths
hem leg opening ÷ 2 − 1, knee = hem + 2 + extra knee width ÷ 2
hem 42.0 ÷ 2 − 1, knee = hem + 2 + 0.0 ÷ 2
The front leg is 2 cm narrower than the back at the knee and hem so the side seam and inseam sit straight on the leg.
Step 13–14
Front waist
Waist ÷ 4 + waist ease ÷ 4 − 0.5 + front dart
= 88.0 ÷ 4 + 2.0 ÷ 4 − 0.5 + 1.5 = 23.5 cm
The centre front comes in 1 cm at the top to shape over the stomach. The waist width includes the dart, which is sewn out again, and the side waist point lands where the width runs out.
Step 13–6–7
Front rise
straight to the seat line, then curved to the fork: 31.6 cm
The rise is straight down the front of the body and curves only below the seat line, where it turns under between the legs.
Step 7–10–12
Inseam and side seam
fork → knee → hem, waist → hip → knee → hem: 74.1 cm
The inseam curves gently in from the fork to the knee and then runs straight to the hem. The side seam goes from the waist over the hip and down through the knee.
Step 13
Outline of the front
The front sewing lines, with the dart, the fly and the pocket opening marked.
Back
Step 1
Back depth lines
same as the front
The back uses the same crotch, seat, knee and hem lines, so the seams of the two halves match in length.
Step 3–6
Back seat width
Seat ÷ 4 + 1 + seat ease ÷ 4
= 102.0 ÷ 4 + 1 + 6.0 ÷ 4 = 28.0 cm
The back takes 1 cm more than a quarter of the seat, the centimetre the front gave up.
Step 6–7
Back fork
Seat ÷ 16 + 4.5
= 102.0 ÷ 16 + 4.5 = 10.9 cm
The back fork is much longer than the front because it wraps under the seat. It drops 1 cm so the back inseam is a touch shorter and is stretched onto the front, which keeps the back leg from sagging.
Step 6–13
Centre back
in at the waist, up
3.5, 3
The centre back is tilted: raised 3 cm so there is length to sit and bend, and taken in at the top because the waist is smaller than the seat.
Step 8–12
Back crease, knee and hem
hem leg opening ÷ 2 + 1, knee = hem + 2 + extra knee width ÷ 2
hem 42.0 ÷ 2 + 1, knee = hem + 2 + 0.0 ÷ 2
The back crease halves the back leg, and the back knee and hem are 2 cm wider than the front.
Step 13–14
Back waist
Waist ÷ 4 + waist ease ÷ 4 + 0.5 + back dart
= 88.0 ÷ 4 + 2.0 ÷ 4 + 0.5 + 2.0 = 25.0 cm
The waist width is measured from the raised centre back to the side. It includes the back dart, which shapes the trousers over the seat.
Step 13–6–7
Back rise
along the tilted centre back, then round to the fork: 38.6 cm
The back rise follows the tilt of the centre back down to the seat line and curves round under the seat to the fork.
Step 7–10–12
Inseam and side seam
as on the front: 73.4 cm
Same course as the front. The fit checks compare the inseams and side seams of front and back.
Step 22
Outline of the back
The back sewing lines with the dart and the jetted pocket marked.

The finished pieces

Trousers, size 50. Front (2×), Back (2×), Waistband (1×). Seam allowance is added afterwards.

The two inseams. The back inseam is drafted slightly shorter than the front. When sewing, it is stretched between the crotch and the knee to meet the front, which shapes the back of the thigh. In wool it is often pressed into shape first.

Sewing it

Cut and mark. Cut every piece with the grain arrow parallel to the selvedge. Transfer the notches, the dart points and the marks with tailor's chalk or a short snip into the seam allowance.
Interfacing. Fuse interfacing to the collar, stand, cuffs, waistband, facings and front edges before sewing anything.
Darts. Sew each dart from the wide end to the point, the last stitches right on the fold. Tie the threads at the point, do not backstitch. Press waist darts towards the centre, bust darts downwards.
Pockets. Make the side pockets and the back pocket while the pieces are still flat.
Fly zip. Sew the front crotch seam up to the zip mark and set the fly zip.
Side seams. Sew the side seams, front to back, matching the notches at the seat and the knee. Press open.
Inside leg. Sew both inside leg seams. The back is a little shorter: stretch it between the crotch and the knee to meet the front.
Crotch seam. Sew the back crotch seam from the zip round to the centre back waist. Stitch the curve twice.
Waistband. Sew the waistband on, the overlap at the fly. Fold, stitch in the ditch, add a button or hook and the belt loops.
Hem. Try on, mark the length, press up and stitch the hems by hand.

Draft it to your measurements Watch it drawn in the editor Practise in the course

Trousers

What you need

Drafting, step by step

Side line

Crotch depth

Seat line

Trouser length

Knee line

Front seat width

Front fork

Crease line

Knee and hem widths

Front waist

Front rise

Inseam and side seam

Outline of the front

Back depth lines

Back seat width

Back fork

Centre back

Back crease, knee and hem

Back waist

Back rise

Inseam and side seam

Outline of the back

The finished pieces

Sewing it