Fitting The Iris Knickers

Fitting the Iris Knickers - Tilly and the Buttons

Making the Iris knickers and need a little extra help getting the fit just right? Well, you’ve come to the right place! This post will cover the most common fitting adjustments you might want to consider for your Iris undies. 

The Iris knickers, designed in collaboration with Hannah from Evie la Lùve, are a simple and versatile knickers pattern with a choice of low, mid and high leg openings and waistlines that you can mix and match to create your fave style of undies. This means there are 36 possible combinations of how to sew them. With so many to sew we best get cracking!

Fitting the Iris Knickers - Tilly and the Buttons


The wonderful thing about sewing is that we can alter our makes to fit the unique proportions of our bodies, getting a much better fit than anything we can buy on the high street. We all have preferences as to how our clothes fit – especially our undies! We sometimes suggest that you make a ‘toile’ aka a practice garment when making a new pattern to test the fit. As the Iris knickers are made from forgiving jersey and are quick and simple to make, you might want to treat the first pair you make as a practice fit pair. If they fit perfectly then that’s great! If they need a couple of tweaks then you can make some small adjustments for your next pair with one or some of the following adjustments 🙂

In this post we’re going to cover:

  • Choosing your size 
  • Lengthening or shortening pattern pieces
  • How to combine pattern sizes 
  • Adjusting the crotch width

Fitting the Iris Knickers - Tilly and the Buttons

Choosing Your Size

Taking accurate measurements is the first step in making sure that your knickers will fit. The two measurements you will need to determine your size are your waist measurement and your hip measurement. 

Using a flexible tape measure, find the circumference of your:

  • Waist – the narrowest point around your middle, where you bend at the side 
  • Hips – the fullest part of your bum (not around your hip bones, as the name suggests, which is higher up) 

Check the tape measure is sitting level with the floor all the way around. It can help to turn to the side and look in a mirror to check. Below are the body measurements for both UK 6-24 & UK 16-34 size bands:

Fitting the Iris Knickers - Tilly and the Buttons

Fitting the Iris Knickers - Tilly and the Buttons

Circle your measurements on the ‘Body Measurements’ chart in the pattern instructions. If your measurement falls between a size (for example, if your waist is 39in rather than 38in or 40in), it’s usually better to choose the larger size as you can take it in more easily than you can let it out.

If your measurements fall into one size on the body measurements chart, that is your size. Take a look at the size key on the pattern sheets and find the corresponding size line. Each size has its own solid or dashed line to make it easy to spot and help you follow it easily. 

If your waist and hip measurements fall into different sizes, do not fear! Sewing our own clothes means we can make gorgeous garments that fit our beautifully unique bodies. Yay! You can join up different size lines at the waist and hips to create a garment that fits your unique body measurements perfectly. See ‘How to combine pattern sizes’ below for more details.

If your measurements fit both size bands, choose the one where your waist and hip size are closer together. The 16-34 pattern has been drafted for proportions with a slightly fuller tummy than the 6-24 pattern, or less difference between the waist and hip measurements.

But first, before you combine pattern sizes you might want to consider…

Lengthening or shortening the pattern pieces

This is something you may have to do consistently in your dressmaking, but do you need to do this when making knickers? Usually, knickers cover a small area of the body and don’t need to be lengthened or shortened by any considerable amount, the exception being for a high waist style. 

If you know you have a particularly long or short torso you might want to adjust the length of your pattern pieces before you sew a single stitch, but mostly you won’t really know if the high waist style is the right height on you until you’ve made a tester pair. If you’re knickers fit fine around the hips but there are horizontal wrinkles across the body and they sit higher than your waist (the smallest part of your torso), then this indicates that they’re a bit too long in the body. On the other hand if your knickers keep sliding down and sit lower than your natural waist then you might want to lengthen the pattern pieces.  

Fitting the Iris Knickers - Tilly and the Buttons


How to lengthen the pattern pieces 

Work out how much additional height you want to add to your pattern pieces. Draw a horizontal line around halfway along the side seam of your front and back pattern pieces, at a 90 degree angle to the centre front/centre back arrow. Cut the pattern piece in half along this line. 

Fitting the Iris Knickers - Tilly and the Buttons

Grab a piece of paper a bit wider than your pattern piece, and draw a horizontal line in the middle. Next, draw a horizontal line below it, the distance between the two lines being the amount you want to lengthen the pattern pieces by. So, if you want to lengthen your knickers by 15mm (5/8in) draw two horizontal lines that distance apart. 

Stick the top part of the knickers pattern piece down on this bit of paper, matching up the bottom of the knickers with the top line. Using a ruler, continue the “place on fold” arrow on the new bit of paper to the top of the bottom line. 

Fitting the Iris Knickers - Tilly and the Buttons

Stick the bottom part of the knickers pattern piece on the bit of paper, lining the top of the pattern piece up with the bottom horizontal line, and match the “place on arrow” line up vertically with the line you just drew. 

Fitting the Iris Knickers - Tilly and the Buttons

Draw a new side seam from the top of the waist opening to the leg opening, keeping the same overall shape. 

Remember to make the same adjustment to the front and back pattern pieces, else you’ll have wonky undies! 

Fitting the Iris Knickers - Tilly and the Buttons


How to shorten 
the pattern pieces 

Work out how much length you want to remove from your pattern pieces. Draw a horizontal line around halfway along the side seam of your pattern piece, at a 90 degree angle to the centre front/centre back arrow. 

Draw a new line above it, with the distance between the two lines the amount you want to shorten the pattern pieces by. So, if you want to shorten your knickers by 15mm (5/8in) draw two horizontal lines that distance apart. Cut the pattern piece in half along the bottom line. 

Fitting the Iris Knickers - Tilly and the Buttons

Move the bottom part of the pattern piece up to the top line, lining up the “place on fold” arrows. 

Fitting the Iris Knickers - Tilly and the Buttons

Draw a new side seam from the top of the waist opening to the leg opening, keeping the same overall shape. 

Remember to make the same adjustment to the front and back pattern pieces, else you’ll have wonky undies! 

How to combine pattern sizes

Don’t be surprised if your waist and hip measurements fall across different sizes, mine do! If yours do too you can very easily combine sizes to create the perfect fit. 

Whether you need to combine sizes or not comes down to which waist height variation you are making. If you plan to make only the low rise waist variation, you can just cut and make the pattern according to your hip measurement. This is because the waistline of the knickers doesn’t reach high enough on your body to be affected by a smaller or larger waist measurement compared to the pattern size. 

If you’re sewing either the mid or high rise waist variations and your waist and hip measurements fall across different sizes, you can combine sizes for the perfect fit.

Fitting the Iris Knickers - Tilly and the Buttons

Whether your waist measurement is a size or two up or down from your hip measurement, the method to alter it is the same (wahey!). Draw in a new side seam, from your selected size at the waist to your selected size at the hip. Use a pattern master, French curve, or even draw the line by hand to get a smooth, curved line. 

Once you have drawn in a new side seam, make sure it is the same on the front and back pieces. The easiest way to do this is to use the first pattern piece you altered as a template and copy the same curve to your other pattern piece. Simple!

Fitting the Iris Knickers - Tilly and the Buttons


Adjusting the crotch width

This is an area that is super personal and one where we all have our own preferences on fit and coverage. You may feel the crotch area on the Iris knickers is too narrow and not giving you enough coverage, or you may feel it’s too wide and creating a bulky and uncomfortable fit. If you feel like you want to alter the crotch fit then fear not! This is a really simple adjustment that will go a long way in ensuring you have a comfy pair of knickers!

Fitting the Iris Knickers - Tilly and the Buttons

To do this adjustment it’s easiest to start with the crotch lining. If you’re adding width to the crotch area, stick your crotch lining piece to a slightly bigger piece of paper. Work out how much you want to increase the crotch by at the sides – the green lines in this diagram shows the crotch lining brought out by 1cm (3/8in) at the widest point. 

To do this, mark the amount you want to increase the crotch by – 1cm (3/8in) in this example – out from the narrowest bit of the crotch. Starting on one side, we want to draw a smooth, curved line from the top of the crotch to the bottom, whilst hitting the mark we just made. Each adjustment will look a bit different but it should look something like the green lines diagram above! 

If you want to reduce the width, it’s exactly the same process, except you draw your new line onto the crotch lining pattern piece instead. In the diagram above this is shown in pink. 

Once you’re happy with your new crotch line, fold the crotch piece vertically in the centre and trace this curve onto the other side of the pattern piece. This will ensure that the curves match on both sides of the crotch lining. Trim away the excess with scissors.

Fitting the Iris Knickers - Tilly and the Buttons

Now we need to transfer the new crotch curve onto the front pattern piece. Line up the right side of crotch lining with the bottom of the front piece, making sure the top of the crotch lines up with the notch on the leg opening. The front is cut on the fold where as the crotch lining is cut flat which is why only half of the crotch lining lines up with the front.

Pin the crotch lining to the front and draw the new crotch curve – and voila you’re done! 

Fitting the Iris Knickers - Tilly and the ButtonsFitting the Iris Knickers - Tilly and the Buttons

I hope this post has helped you decide if you need to do any fitting adjustments to your Iris knickers. Don’t get too carried away with fitting adjustments though – remember these are undies so won’t be seen by anyone! 

For LOTS more help with your knicker stitching adventures, sign up for our new online workshop:

LEARN TO SEW KNICKERS

We love seeing your finished makes and progress shots. Tag us on Instagram @TillyButtons using the hashtag #SewingIris to share your gorgeous undies with us!

*****

Authors: Hannah Bullivant, Abi Dyson and Nikki Hoar
Models: Averil de Souza and Andii Melody Mae
Photographer: Jane Looker
Hair and makeup: Julie Wong

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