The basic pants pattern is one of the pillars in flat pattern drafting. There are great benefits for both home sewers and clothing designers to know how to draft. But all those numbers and steps to follow are so frustrating, right?
Well, they don’t have to be. Drafting a pattern from measurements doesn’t have to be difficult and intimidating.
You might be thinking:
Why do I need to learn flat pattern drafting and especially how to draft the basic pant sloper? I am not going to lie – flat pattern drafting can be boring and there is simple math involved. This is simply a process of following some monotonous steps of drafting and connecting dots. But it is necessary for any clothing designer. The reason is – it will make your designing efforts easier, not harder.
What is basic pants/trousers flat pattern making?
This is the process of building up an actual sewing pattern that fits certain body measurements. The basic pants sloper is usually used for woven fabrics and has a classic silhouette. There are ways to modify it into various styles according to your designer vision.
this article is about drafting a pattern from custom measurements, not altering a pattern. There is a difference between those two terms. Altering the pattern is a subject we are going to deal with in some of the following tutorials.
Ways to approach drafting the pattern.
There are different approaches to drafting the pattern – some chose to build the front panel first. Then, on top of it to build up the back panel. I prefer to use a method according to which both front and back panels of the pants pattern are drafted simultaneously. This way the pattern is much easier to modify once it is drafted.
You might find another technique more appealing, so feel free to use the one that works best for you. There is no right and wrong here. Also, this is a tutorial on the basics of drafting the pattern. If you would like to get a deeper into the subject and follow up with muslin adjustments and refining the fit, you might find this Patternmaking + Design: The Pants Sloper course useful.
Taking the body measurements.
Taking the body measurements is the first step in the process. It is very important to take the accurate measurements. If
they are not accurate, it might influence the final result significantly.
Measurements and calculations for drafting a flat pants pattern:
- ¼ Waist
Measure the waist at the smallest. Or, if you prefer the pants standing lower on the hips, measure that circumference. Divide it by 4, because we are going to work with 1/4 of the pants details.
- ¼ Hips
Measure at the widest part of the hips. Again, divide this number by 4.
- Crotch depth/rise
You can get this measurement by sitting on a chair and holding a ruler next to your hips. Measure from the chair up to where you want those pants to stand.
- Hip depth
This is the distance between the waist and the hips you just measured.
- The magic formula. To draw the crotch curve, we will need to know how far we should extend it on both the front and the back pattern detail. There is a simple formula to help us with that.
Front crotch extension formula: Back crotch extension formula:
15% of ¼ hip 45% of ¼ hip
Or, once you’ve calculated the front crotch using the formula above, just multiply it by 3 to get the back crotch.
Measure the overall length of the pants on the outer leg. Start from the waist (or a bit lower if you prefer lower rise) and measure down as long as you want the pants to be.
2. Building the pants/trousers sloper.
2.1 Outline the pattern.
The first step to take when drafting the pattern is to outline it. We are going to do that by drafting a rectangle as follows:
- From point A to B, use a half of the hips measurement (or 2 times 1/4 hips). From B to C and from A to D, use the overall length.
- Divide the rectangle in half so that you get two 1/4 hip wide panels. Mark the points that cross the horizontal lines as 1 and 2. We work with a quarter hip because we are going to draft a front and a back panel. We use each of them twice to cut two fronts and two back pieces of the pants (FIGURE 1). That gives us a total of four details to work with.
- The next step would be to apply the hip depth. Starting from A and B, apply the hip depth and mark points E and F. Connect them with a dotted line. Mark point 3 where the new line crosses the vertical line in the middle.
- Again, starting from A and B down, apply the rise and mark points G and H. Connect them with a dotted line. Mark point 4 where the new line crosses the vertical line in the middle.
- Start from the bottom line and apply the knee level, marking points I and J. Mark point 5 where the new line crosses the vertical line in the middle.
Now that we have the pattern outlined, let’s start
2.2. Drafting the front panel of the pants pattern.
- start with measuring 1 inch (2.5 cm) down from point A to point D and mark point K.
- From point K, measure an inch (2.5 cm) towards the middle and mark it as point L.
- From point L, apply 1/4 waist measurement and draw a line that connects with the horizontal line of the rectangle. Mark point M.
- Connect M with 3, and 3 with 4.
- From point G, extend the line as long as we calculated the front crotch (using the formula above) and mark as point N.
- from point G, draw a ⅗ inch (1.5 cm) long line at 45-degree angle and mark point O.
- connect points N and L, passing trough the new point O and E to create the crotch curve.
- measure 1.2 inches (3 cm) from points 5 and 2 in (on both knee and hemline) and mark points P and Q.
- connect N–I–D and 4–P–Q to form the leg shape.
- connect D and Q to finish the front panel at the hemline.
The last thing we need to do here is to make the lines more natural and smooth as we are used to seeing them on patterns.
We are going to do this in the final step. For now, let’s begin
2.3. Drafting the back panel of the pants pattern
- Start by measuring 1 inch (2.5 cm) from B towards A and mark point R. From point R, measure another inch (2.5 cm) straight up and mark point S.
- From point S, apply 1/4 waist measurement plus 1 inch (for the dart) and draw a line that connects with the horizontal line of the rectangle. Mark point T. We are going to draft the dart later. Connect T with 3, and 3 with 4.
- from point K, extend the line as long as we calculated the back crotch and mark as point V.
- starting at point K, draw a 1 ¾ inch long line (4.5 cm) at a 45-degree angle.
- from point F towards B, measure an inch (2.5 cm) and mark point U.
- connect points S and V, passing trough the end of the 45-degree angle line and the new point U to create the back crotch curve.
- extend from point M out ¾ inches (2 cm)and mark point W.
- do the same from point C out and mark point X.
- starting at points 5 and 2, measure 1/2 inch (1 cm) in and mark points Y and Z.
- connect V–W–X and 4–Y–Z to form the leg.
- connect Z and X to finish the back panel at the hemline.
1.3. Final adjustments.
- when we drafted the back panel of the pants sloper, we left an inch (2.5 cm) for a dart. To make it, measure and mark the middle between points T and S. Apply half an inch in both directions. Draw a 2 inch (5 cm) long perpendicular line. Connect the end of that line with both sides of the dart. This will result in a dart that is 1-inch deep.
- now, let’s make the curves of the pattern a bit more natural. Draw a perpendicular line 1/5 inch (0.5 cm) right in the middle of lines O–3 and T–3. Redraw those lines, making a small curve that passes trough the end of that 1/5 inch (0.5 cm)- long line.
- do the same with the inner leg lines Q-L and V-W. Instead of drawing the curves out, draw them inwards to make the curves.
- make sure that the inner leg of the front pattern piece matches the back’s inner leg. If there is a slight difference, just move point V accordingly up or down a little and redraw the back crotch curve.
These were the final steps in drafting a pants/trouser pattern. Please, have in mind that this is the very basic sloper that can be modified in various ways.
You can modify the length and width of the legs, add a zipper fly and pockets, change the depth of the darts, etc. You can also tailor it once you’ve drafted it.
For example, you can remove wrinkles on the crotch or bottom, lengthen or shorten it in the hips area, etc. Here is a good course on that: One Pattern Many Looks
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