Let’s draft some pants with these Trousers Pattern Instructions. I’m bringing you a step by step tutorial on how to draft your first pair of trousers. Before we start, let’s make something clear! Trousers are very difficult to get right, so expect around 5-10 prototypes before you get the perfect fit! It’s okay to get frustrated but I can promise you that all the work will be worth it!
Measurements
Let’s look at what measurements we’re going to need first. Remember to wear underwear that is not too restrictive and that you would wear below your trousers. Also, when you take the measurements, don’t press on the measuring tape too much. Finally, it’s okay if the measurements are not precise, you’ll be able to fix that in the prototypes.
WAIST CIRCUMFERENCE
Measure the circumference of the thinest part of your torso, below the rib cage. I’ll show you how to modify the pattern for high-waisted and low-waisted pants later on.
HIP CIRCUMFERENCE
Measure the circumference of the widest part of your lower body. This is normally the hips but your widest part can sit lower. If you want more precision, you can always measure the front and back hip arches separately (from side to side).
TROUSERS LENGTH
Measure the vertical line from the waist to how long you want your trousers to be. Best results are when you measure until your ankle bone. They can be made longer or shorter later on.
HIP DEPTH
The hip depth is measured from where you measured your waist to where you measured your hips, on the side of your body.
CROTCH DEPTH
To take this measurement you have to sit on a flat surface and measure from your natural waist (or where you measured it) to the flat surface. Measure it on the side of your body.
CROTCH LENGTH
Measure from the front to back waist, going in between the legs following the crotch shape. This measurement is optional to check the pattern before prototyping.
With that we have all the required measurements, but there’s a couple of optional ones that will be handy:
- Upper thigh circumference: This measurement is used to check the allowance around your upper thigh. Measure around the top part of your thigh just below the crotch
- Knee circumference: This measurement is used to check for ease around the knee. You need enough ease to allow for mobility. Measure around your knee while bended.
- Ankle circumference: This measurement is used to make sure the trousers will fit your foot. Measure around your foot and heel.
Instructions
Step 1 – Structure
Step number one is to build the structure of our trouser foundation. We start at the top left and mark 0.
- 0 – 1: Trousers length measurement
- 1 – 2: Half the hip circumference plus 1.25cm
- Finish drawing the rectangle
- Divide the structure: From the line 0-1 half way to 1-2 plus 1cm. The front is on the right and the back is on the left.
Step 2 – Main Lines
Once the main structure is ready, let’s draw the main lines that will define the shape of the trousers
- The line 0 – 3 is the Waist Line
- 0 – 4: Waist to hip measurement. This is the Hip Line. Mark 4,7 and 10
- 0 – 5: Crotch depth + 2cm. This is the Crotch Line. Mark 5, 8 and 11
- The line 1 – 2 is the Ankle Line
- 1 – 6: Half the distance between the crotch line and ankle line + 2.5cm. This is the Knee Line. Mark 6, 9 and 12.
Step 3 – Crotch Curve
Let’s start drawing the actual trousers. We’re going to start by shaping the crotch curve.
- 5 – 13: Half of the distance between 5 and 8. This is the back crotch extension.
- 11 – 14: One quarter of the distance between 8 and 11. This is the front crotch extension
- 0 – 15: Draw a line half way between the waist line and the crotch line. Mark where this line crosses the main rectangle.
- 0 – 17: 2cm
- 3 – 18: 0.5cm
- Back curve: Draw a curve from 13 that goes 5cm outside of 5, through 15 and to 17.
- Front curve: Draw a curve from 14 that goes 3.75cm outside of 11, through 10 and to 18.
Step 4 – Waist
Next step is to draw the Waist. For that we’ll need to make some assumptions about darts.
- 17 – 19: 1/4 of the waist circumference + total dart measurement + 0.5 cm ease
- 3 – 20: 1/4 of the waist circumference + total dart measurement + 0.5 cm ease
Darts are our way to create rounder shapes in the pattern. Every body will need different measurements. The rules are:
- Darts should be maximum 3 cm wide. After that they should be divided by 2.
- 2 darts are used for larger hips/small waist and 1 dart for more rectangular bodies.
- The same stands for the belly
As a standard dart measurement you can use:
- Front: 2 darts of 1cm each. This is a total of 2cm.
- Back: 2 darts of 2cm each. This is a total of 4cm.
Step 5 – Darts
As explained before, darts will depend on your body. This is the standard way of drawing them but use the ones that suit you best.
- On the back side (left on the drawing) we’ll draw 2 darts of 2cm each. The first one is placed at 7.5cm from 17 and the second one is 3cm away from the first dart.
- On the front side (right on the drawing) we’ll draw 2 darts of 1cm each. The first one is placed 7.5cm away from 3 and the second one is 3cm away from the first dart.
The darts on the back are 11cm long and the ones on the front are 7.5cm long.
Step 6 – Leg lines
To define the leg lines, we need to find the crease line. That is the line that divides the trouser legs in the middle.
- 8 – back crease-line: Half the distance 8 – 13 plus 0.5cm
- 8 – front crease-line: Half the distance 8 – 14 plus 0.5cm
Draw a line perpendicular to the crotch line. From there we can draw the width of the trouser hem:
- Back: 11cm on each side
- Front: 10cm on each side
These measurements are standard and can variate depending on the desired width. Normally the back width is wider than the front one.
Step 7 – The Trousers
Now you have all the points to draft the trousers.
- Back: Draw a curve from 19 to 7 and then to your ankle width. For the inside of the leg draw a line from 13 with an inward curve to the ankle width.
- Front: Draw a curve from 20 to 7 and then to your ankle width. For the inside of the leg draw a line from 14 with an inward curve to the ankle width.
And this is it, you have your Trouser foundation Pattern ready! Before prototyping I’d advice you to check a couple of things just in case:
- Make sure there’s enough ease around the upper thigh, knee and ankle compared to the optional measurements you took earlier.
- The crotch length in your pattern should be the same or longer than the one measured on your body.
- The side seams of front and back should be the same length, otherwise change them to be the same.
To modify the pattern into other designs, more information on how to do it here.
If you want a video explanation, here you have it (Be aware that the correct numbers are ALWAYS the ones on this article and not the ones on the video, as it is difficult to correct errors once published):