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Correcting Back-leg Wrinkles on Pants

Threads #98, Dec/Jan 2001/2002

Correcting Back-leg wrinkles on pants

Most of my pants have long, diagonal lines in the back from the high-hip area to the inside thigh above the knee. I have a long torso and a flat derrière. How do I get my pants to fit wrinkle-free?

—Bertha Tribuno

The diagonal wrinkles you describe indicate that the fabric is hanging off-grain, says fitting expert Karen Howland, not because it’s cut off-grain, but because it’s being supported off-grain. Try this experiment: Hold a large rectangle of fabric, such as a bath towel, in front of you. When you hold the corners equidistant from the floor, the fabric hangs smoothly. Now lift the right side higher than the left. The sides of the towel still hang straight, but the top and bottom are at an angle. The fabric adapts to the change in support and hangs with a diagonal drape angling from the highest corner to the lowest one. In essence, this is also what’s happening to your pants, except they aren’t rectangular. The fabric grainline may exactly follow the mid-line of the pants leg, but the pants will only hang wrinkle-free if the upper support allows them to. 

Pants hang from the hip and high-hip area. When all’s well, the pant lengths at the side and center back are appropriate for the shape of this supporting area. Your diagonal wrinkles indicate that your pants are not long enough on the sides, because the wrinkles point directly there, toward the part of the support that’s too high. 

So, let’s take some measurements to see exactly what’s going on. I’ll assume that the front of the pants fit correctly, and concentrate on back-pattern adjustments. Wearing comfortable pants, use the bottom edge of the waistband interfacing to define the waistline for the following measurements. To find your side-seam length, measure from the waistline to the floor at both right and left sides, subtracting the distance you want from floor to hem. Determine your center-back length by measuring from the floor to the waist (following any desired dip under the derrière, as shown in the far left drawing below, also subtracting the distance you want from floor to hem. 

To measure and record the shape of the crotch curve and inseam, use a long flexible curve—mine’s 40 in. long. Mark the front- and back-waistline points and inseam location with rubber bands slipped over the curve and rolled into position. Measure the inseam with the flexible curve in place, using it to establish the top of the inseam. Find your crotch depth by subtracting the inseam length to the hem from the side-seam length, as shown in the drawing. Tilt the top of the flexible curve to the side and carefully step out of it. With a long torso and a flat derrière, your curve may look something like that below. 

Now let’s compare these measurements to your pattern. Check the crotch depth-first. Draw a line perpendicular to the grainline across the pattern from the top of the inseam to the side seam, as in the drawing below. Measure the crotch depth from this line at the side seam to the waist, lengthening (by slashing and spreading) or shortening (by tucking) the pattern as needed to correspond (adjust the front pattern to match, of course). Also, check the inseam measurement, and adjust the leg length as needed. Double-check the side-seam length. It should now be the desired length. 

To compare and correct the center-back length and the crotch curve, place the pattern’s upper half over another sheet of paper. Measure from the hem toward the waist the length you established for the center-back length. Draw a line parallel to the crotch line at this distance on the paper underneath. The waist at the center back should meet this line. If it is above this line, as in the drawing at left, the center-back length is too long, and is best corrected by adjusting the tilt of the upper pants: Slash the pattern from the center back at the hip level to the side seam at the crotch-depth position, as shown in the same drawing. Pivot to overlap the pattern where slashed until the center-back/waist point contacts the back length line. 

While adjusting the tilt, you need to maintain the desired crotch length and shape in the back. This was found with the flexible curve, on which you marked the inseam position and back waistline. Straighten out the curve above the hip level to match the shape of the center-back seamline, but allow the curve to hold its shape below the hip level. Position the curve on the pattern, matching the waist points, as shown in the drawing at left below. The differences will happen below the hip. The curve will probably dip below the crotch line and return to it to meet the inseam.

If you need still more length, slash and pivot the upper pants pattern from 4 in. below the crotch line at the side seam, adding the same amount at the inseam until the curve fits, and keeping the back waist on the back-length line, as in the drawing at left. For a flat derrière, leave your back darts unstitched until the first fitting, when you can pin in the needed darts. 

To measure center-back length

Include any contouring you want beneath the derrière by shaping your tape measure to follow that contouring, then subtract the floor-to-hem distance you want.

diagram how To measure center-back length

To find crotch depth 

diagram how To find crotch depth 

Use flexible curve to copy crotch shape

diagram of how to Use flexible curve to copy crotch shape

To correct center-back length

diagram To correct center-back length

To adjust for crotch curve

Straighten flexible curve to match CB above slash. Redraw the crotch to match the flexible curve. Spread at side seams and inseam if necessary for more crotch length without changing other dimensions.

To adjust for crotch curve

Here’s the place to get some answers to your fitting questions. If you have a better solution than the one we’ve given here, please write and tell us. Send your questions (include photos, if possible), comments, and solutions to: Threads Fitting, PO Box 5506, Newtown, CT 06470-5506 or via e-mail ([email protected]).

Previous: Alterations for Perfect Pant Legs Next: Fitting the Seated Figure


  1. user-7905714 | | #1

    At the step of correcting crotch depth, why does the image show the slash/spread happening on the crotch curve side rather than the side seam side of the leg?

    1. [email protected] | | #2

      That's an excellent question that I was wondering about myself. I think they are using the slash and spread to adjust back seam length to match the flexible shape ruler. It must be that. But I know I always have to do this.

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