Saturday Simple Sewing Hint: Key+String Crotch Measuring Tool

The ‘Key’ (no pun intended) to a great pant fit is a thorough understanding of the Crotch Depth and the Crotch Length AND how to measure for each.  

 I learned and then have taught for years that one measures and alters for the Crotch DEPTH first, as seen below.  The one thing I see missing in this photo is a string or elastic around the ‘waist’ – or wherever one wants the top of the pant to rest.  That spot can NOT ‘float’ around.  It must be established and defined clearly for and throughout this process.  The way I like to explain the difference is that CROTCH DEPTH is more an indication of skeletal structure, and CROTCH LENGTH reveals the ‘fluff’ (derriere and tummy).

crotch depth

Measuring Crotch Depth

Altering Crotch Depth

Alter for Crotch Depth

Altering the CROTCH DEPTH is done first, because that 0bviously effects the CROTCH LENGTH.


The ‘Key’ that is being shared here is this TOOL for measuring CROTCH LENGTH.

  1. Again, with the ‘waist’ established on the body, take a TOOL like this (long string with a Key tied to the middle of it).
  2. Holding the Tool ‘string’ at the waist in back, bring it between the legs, placing the KEY at that point of your body where you want the inseams to intersect the crotch seam, then bring the string on up around to the waist in the front.
  3. Pinch the string at the waist points, step out of this ‘basket’ measurement, keeping Front and Back defined, and measure –
  •  from point on string in the BACK to the Key = Back Crotch Length
  •  from point on string in the FRONT to the Key = Front Crotch Length

crotch length measuring string

Can you see the ‘basket’ created by the Pant?  It’s the ‘basket’ into which your body must fit.  On most of us, the BACK CROTCH LENGTH will be the larger than the FRONT CROTCH LENGTH.  A ‘forward’ located inseam is what European (Burda) Pant patterns are known for.  Doing this creates a larger bias area under the derriere that gives a better fit – is the way I understand it.


Then, of course, their is WEARING Ease.  Unless we are talking about Leggings of knit fabric, there needs to be additional ‘wiggle room’ added to body measurements for wearing comfort.  Here is a chart I found from The Sewing Workshop for what to add.

Crotch Length 1″ – If hips are less than 37″

1½” – If hips are 37″-40″

2″ – If hips are 40″ or more

In general, I always ascribe to the fact that if it is cut in, you can always take it out, but it is harder to go the other way.  Ease is a comfort issue and that cannot be defined by anyone but YOU in the garment WITH the undergarments worn that you will be wearing with the garment.  (A body wearing SPANX will measure and ‘wear’ differently than one NOT wearing SPANX.)


I believe it was Pati Palmer who said one should stitch and fit pants in their underwear and I agree!

The other thing I learned from Pati was to be sure to cut it plenty tall at the top ‘in case’.  Then, to FIT AS YOU SEW, (again with the proper undergarments worn), pull on the pants, and then place an elastic EXACTLY at the location where you want the top of the pants to be, adjusting for comfort and inseam location, etc.  MARK clearly all around the waist.  Doing this is the easiest way I found to adjust for a high hip, fabric ‘drape’, etc.

BITE THE BULLET and just get some basic pants FITTED!

Honestly, during my ‘retail storefront years’ I did so many pant fittings, I really HATE to do pant fittings now.  I long ago came up with my own pant patterns.  It’s worth it to me to keep my body the same so that I don’t need to do it all over again.  However, I’m finding in my Sunroom Sewing Studio classes, that those days are returning.   Since we all wear pants SO very much, it is an important thing to grasp and work through for yourself.   Hopefully this ‘TOOL’ for crotch length measuring will be helpful.

If you have a specific question regarding pant fitting, be sure to put it in the COMMENTS here.  I’ll answer just as soon as I am able.  Many great sewing products are waiting for you at my website:

Come and visit – I’m confident you’ll be glad you stopped by!

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30 Responses

  1. Great tips Londa! I discovered that Sandra Betzina’s patterns follow the Burda block for pants which is probably why they often fit me so well. Palmer/Pletsch also has a great pants pattern now on sale at McCalls that includes loads of instruction to help people through the fitting process (M7445).

  2. Robbie says:

    Thanks for posting this (much needed) information.You mentioned a ‘forward located inseam’. Years ago, I owned a pantsuit where the pants fit beautifully. They soon wore out so I cut them apart and saw the difference in crotch shape. As a newbie sewist, I could not duplicate that fit. In hindsight, the pants had a European cut. How can I adjust my pants sloper to this type of fit? You listed Burda patterns as having this type of inseam. I will be checking my archived patterns for Burda pants.

    • admin says:

      You can make this adjustment. Simply cut off the front pattern inseam and add to the back. Remember though, that seams that go together (lengthwise ones) need to have the same ‘shape’ to work together. Do that cut and move, then lay on top of each other to tweek the shape of the cutting line. MUSLIN or cheaper (but same drape/give) sewing time.

  3. Sandy says:

    Thank you for the help. l will definately try the key and string with the next pant l draft. l find my measurements are always short when l measure the crotch length after the drafting is complete.

    • admin says:

      I find that always adding an extra inch at the top of pants is a good idea, as I don’t like the ‘low riders’. One can always adjust where the waistline finishes from the top edge – at least that’s the way I do it. Good luck and glad this helps.

  4. Nuz says:

    I find that my back side seam is 0.5 inch longer than the front side seam in my pattern?

    Is this fine? Will the pant length not get alterd.


    • admin says:

      Be sure to sew with a taut technique as side seams are usually almost straight grain. However the length ends up at the hem, it will be OK – but make sure you allow for plenty of hem allowance. I do agree, a well-drafted pattern should have the side seams the same length and silhouette though.

  5. Lizzy says:

    Thanks this was helpful but what should be the crotch depth for a 43″ hips and 33″ waist.thanks

    • admin says:

      Thanks for asking, but there is NO way of knowing. You need to measure yourself.
      You asked using the term, Crotch DEPTHS. Crotch Depths generally run 9-12″, sitting on a chair and measuring from the natural waist down to the chair. This is all about how God made YOUR skeleton, imho.
      Crotch LENGTH is indication of the size of your crotch ‘basket’, of the ‘hole’ into which your tummy and derriere sit. I think it is VERY important. Also – where you want the ‘top’ of your pants to rest – on YOUR body, as few want their pant upper edge up at their natural waist these days. the larger the tummy and/or derriere – well bumps take more length to go over them, so the bigger bumps, the longer the crotch LENGTH.

      • Julia Alaniz says:

        You are correct. Crotch depths/“U”s are highly preference-based. Two (or any number of) people can have the exact same measurements, but very different preferences on how the crotch should fit – some like a tight fit, others a looser fit. For starters, as you point out, the position of the waistline – again dictated by personal preference – is crucial to finding the crotch depth. I developed a “Take 5! “ for my students, as a *starting point* to finding a crotch fit to one’s satisfaction.

  6. Derbe says:

    I made a mistake while making jumpsuit and my client complain of the crotch area too tight how do I retify this…

    • admin says:

      I’m sorry to tell you that from my experience, there is very little you can do to rectify this. You need more crotch length, and the height – the length of the fabric through the area between the waist and the crotch is not there. These are adjustments that must be made on the pattern before cutting – especially on a jumpsuit.

  7. Sue says:

    Hi Derbe
    I don’t want to highjack the discussion, but I have had some success solving this problem. I have fixed this by sewing the crotch seam (the u shaped seam) about one inch further down on the leg seam. Open up the seams at the old junction and try on. If good trim away the old seam line. If still too tight you might try sewing another seam a little further down the leg. I hope this helps.

    • admin says:

      From what I have learned and experienced, this won’t work – but anything is worth a try.

    • Julia Alaniz says:

      Sue, assuming that the only problem is being crotch-bound, your modification (increasing the “U” ) is correct. And your precautionary measure of releasing the existing seam, for a fitting approval – before cutting to make the “U” deeper – is a must.

      Crotch depths/“U”s alterations are like armscye alterations – you can make them deeper/larger/looser; however, once cut, sewn and trimmed, you can not make them shallower/smaller/tighter (other than letting out seam allowances, if there is anything to let out).

  8. Sue says:

    Hi Londa
    I love your string and key tool. What a great idea. The tin foil thing never worked well for me. Thank you for your wonderful blog. So much good information.

    • admin says:

      Happy it helped, and that you’ve found my Blog. We all need as much help with pant fitting as is possibly available, eh?
      I’m always happy to receive ideas for how-to’s, posts, etc.

  9. Enjoyed your article. Now wondering would you use the same theory for buying ladies panty underwear? Hard to find comfortable underwear and how to buy, when they usually come in a plastic bag & only hip measurements. Thanks Mary

    • admin says:

      That is exactly why ladies have such a fit when a brand/style they’ve found gets discontinued. I guess the only solution is to make your own – but I haven’t even ‘gone there’ as yet.

  10. Pratap Saini says:

    what is the standard front crotch length in m size

    • admin says:

      There is no way of telling you that – Medium can mean many different things! The ratio of the front crotch length to the back crotch length varies not only by your figure, but also by the design of the pattern. My best hint would be to find a pair of pants that fits you like you like it to – then measure the front from waist (top edge) down to the intersection of all the seams under the crotch. Record that. Do the same for the back crotch length. Then use those measurements to compare to patterns you are considering.

  11. Roseann Granger says:

    Hi Londa,
    I enjoyed your article very much and believe it will be helppful. I have been taking some online classes with Judy Kessinger of Fitnice Systems. In addition to getting the crotch “basket”, there are often still issues to not have pants bagging in the back. Whether we have “junk in our trunk” or flat behinds or sway backsd; these also make a difference. The junk in the trunk issue will be solved using your method; and the others I mentioned can well be solved with Judy’s method she calls “butt lifts”. They are done on the pattern…yet you need to have cut a practice pair of pants to determine where and how much to adjust. They both serve their purpose well, and we don’t all need one, or we may need one or the other; or both! and that’s okay.. just get us with a pants pattern that fits! Judy also uses the elastic method you refer to and is a firm believer that pants are a “personal fit”; as you say, you are not wearing them.. we are.. and we have to determine what “feels good” while “looking good” at the same time. Thank you for your wonderful help and well worded descriptions and explainations. Very truly yours, Roseann Granger

  12. Can you tell me how to work out the extension of my front and back crotch in easy terms. I have great difficulty in this Alma thanks

    • admin says:

      I’d be happy to try to answer your question but I need some more details. I can highly recommend this book: Pants for Real People by Palmer/Pletsch. I’m sure you can find it on Amazon. I’m confident you would be pleased with all the info you find there. Again though, I can try to answer but I need more details.

  13. Jojo Sewist says:

    Is there a specific point on the center front and center back seamlines that the “curve” of the crotch curve length begins? I hope this makes sense to you. I thought the curve began at the crotch depth line. But I noticed on the drawings that the crotch depth line was the termination point of the center front and center back seamlines/crotch curve length. Please what am I missing? I used to sew and lucky me most pants patterns fit me with little alterations needed. Fast forward 30 yrs. and no pants patterns fit my aged body. I am trying to alter a pants pattern so I can have one to sew by.
    This post was very helpful, especially the tip to draw the reference lines on the muslin. Thank you for sharing your talent.

  14. Lola says:

    Hello Everyone, I would appreciate some help here, what is the possible crotch length for a hip 49 (size 16) woman?

    • admin says:

      Honestly, it doesn’t matter. What matters is what YOUR body measures, and most importantly for FRONT Crotch Length and BACK Crotch Length. Even now, as the ‘waistlines’ of pants move back towards the actual waistline, those measurements will increase. Follow the video. You CAN do this!

  15. Dianne says:

    Your illustration with the string and key really shows you how differently each half of the pants crotch area needs to be. I have found that measuring the crotch length first and adding appropriate ease (about .75 of an inch for me) and then subtracting the total crotch depth from front and back helps me to get a good idea of how much I need for the extensions. example – if my estimated crotch depth is 10.” then I add an inch for ease (now 11.”). Since the depth is the same for front and back, the total is 22.”. If my crotch length is 27.5″ with the appropriate ease, then the difference would be 5.5″. I would then distribute that amount between front and back extensions – 2″ for the front and 3.5″ for the back. I also use the difference between the front crotch length (in your example the center front waist to the key) and back crotch length (from center back waist to key) to estimate the amount to add to the center back height at the back waist. If my difference was 1.25″, I would go up past the waist at the back by that amount. While my method may not be workable for everyone, it sure helps to find a good starting point when drafting patterns.

    • admin says:

      Does make sense. Thanks for sharing. If it works for you – GREAT! I applaud you for specific, reasonable application to achieve your desired results. Way to go!

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