When Lyndon Johnson was president he had many or all of his conversations taped and on those tapes was his conversations with his tailor about how he would like to increase the depth of his pants. Why this was recorded is beyond me but it is a great listen. However, it shows that we all can have crotch problems and they can be addressed.
The two measurements we need to have a perfect fit in the crotch area:
The Crotch Depth: The measurement is the distance from your waist to the bottom of your hips taken when you are sitting down.
The Crotch Length: the actual length of the crotch seam, taken between the legs, from the waist at the center front to the waist at center back. A good way to find the correct length in the front and the back is to measure the crotch length with a string and a set of keys. The keys need to move freely so they find the center of gravity. the string should be pulled snugly up to the front and back waist and the keys should settle. Now, step out of the loop and gently place the keys and the string on your table, measuring the front string which is your front crotch seam and the length behind the keys is your back crotch seam measurement. The keys are at your inseam or center of you body.
The measurement is a good indicator of whether or not you need any adjustments are needed in your waist and the top of your legs. Remember if alterations are needed you will have to alter the side seam and the crotch seam for pattern continuity. When the length of the crotch is altered either lengthening or shortened an additional change–an increase or decrease–must occur in the width of the pants leg at the top of the thigh.
A few rules apply:
The crotch length can be altered at the crotch point of the pattern which is the intersection of the crotch seam and the inseam, or it can be altered along the crotch seam.
You should use the crotch seam method of altering the crotch length if only your stomach or butt is the problem, thus insuring that the right amount is taken away or added exactly where it is needed.
When both the crotch depth and the crotch length alterations are needed, alter the crotch depth first and re-measure the crotch seam on the pattern before altering to fit your needed crotch length.
Altering the Crotch Depth: To increase the crotch depth cut the pattern and spread the full amount needed on the “lengthen or shorten here” line on the front and back of the pattern. To decrease the depth, tuck and fold at the “length and shorten here” line on both the front and back of the pattern. Only tuck half the needed length due to the doubling of the pattern in the tuck.
There are two methods for altering the crotch length:
The Crotch Point Method: Start by drawing a crotch line if it is not on the pattern already. start the line at the side seam and end it at the crotch point; it should be perpendicular to the grainline. To increase the crotch length extend that line at the crotch point the amount you need for the alteration. Draw new cutting lines at the inseam and crotch. To decrease, shorten the line at the crotch point as needed and redraw the lines at the inseam and the crotch.
The Crotch Seam Method: By using the Cut and Spread Method and the Tuck and Fold Method, cut the pattern at the alterations line to the seam line making sure to stop before you cut the pattern in two. To increase, spread as much as you need for the alteration, tapering the line toward the side seam. To decrease, tuck and fold on the alteration line the amount needed, taper the fold so that no change occurs in the line of the side seam.