Why and how
Why pattern alterations are made
Patterns are altered primarily for two reasons: either to improve the fit of the garment or to alter its appearance. With both, the objective is to make the clothing fit the wearer as well as possible, and to ensure they enjoy wearing it.
The aim of fit alterations is to make a piece of clothing into something that is adapted to and suits the wearer’s individual body. Both ready-made clothes and sewing patterns are usually designed for a ‘neutral’ body type, since it is impossible to create a pattern for clothes that will fit everyone with no need for alteration. This is why we often have to refine patterns slightly.
A well-fitting garment looks good and flattering, as its proportions are right and the individual details are at the right points, with no straining wrinkles or excess ease. A well-fitting garment also feels pleasant to wear, does not restrict movement or have to be adjusted from time to time in order for the garment to look and feel good.
Determining the necessity and amount of alterations
The necessity and extent of any pattern alteration depends on the difference between your own measurements and those of the size chart, as well as on the type of the garment. The need for alterations and the number of alterations relate directly to how loose the garment is – the more tailored the fit, the more adjustments may need to be made to the pattern and the bigger the adjustments may need to be. The fit of looser or stretchy garments will not necessarily need to be altered in any other way than the length, and the amount of the alteration for a loose garment may also be smaller than for a tailored piece.
Compare your own measurements to those in the size chart in order to determine how much to remove from or add to the pattern. Never use the finished measurements of the garment as a starting point for pattern alterations, unless you specifically want to alter the ease in the pattern! Instead, always preserve the pattern’s original ease (ease means the difference between the size chart and the finished measurement, and it can also be negative in garments that are made of stretch fabrics). See the detailed measuring instructions and size chart here.
You can also assess and measure where and how much the pattern needs to be altered by studying your toile. If the toile is strained, you can cut it open across the strains and allow the cut to open enough for the strain to loosen. Pin a piece of fabric under the cut, and measure the amount the piece has been opened by. Transfer this addition to your pattern. If the toile is saggy or too loose, the fabric can be sectioned and pinned off into a dart or a pleat, so that the sagginess or excess ease is removed. Afterwards, open the pleat, measure it, and remove the same amount from the pattern.
The 'slash & spread' method
We have used the so-called ‘slash and spread/overlap’ method, where alteration lines are drawn onto the pattern, cut open, with the pieces then slid on top or apart from each other. The alteration lines are drawn with a pink line in our diagrams. Sometimes the lines are cut open so that a small section is left at the end of the line, just a millimetre or so long, as a ‘hinge’, or ‘pivot point’. This pivot point stays in place when the other parts of the pattern move. A small pink dot marks the pivot point in the illustrations.
When moving the pieces, keep a large piece of pattern paper underneath them, to which you can tape pieces that are not moving, and only move those parts that need to be moved. Draw guide lines onto the pattern or the paper underneath it, to help you move the pieces and tape them at the right distances from each other. Once you’ve made the alterations, tape all the pieces carefully in place.
Remove the seam allowances from all the edges the pattern alteration will affect, and add them back in after the alterations. As pattern lines are not always straight, seam allowances do not generally correspond to the shape of the piece, and instead may distort it and complicate the alteration. All our patterns include a 1 cm (3/8”) seam allowance, unless otherwise indicated. Draw the seam allowances on the pattern 1 cm (3/8”) (or otherwise if stated in the pattern) inside the cut line. You can cut off a small section from the seam allowance at parts where the pattern is altered, usually where the slash or pivot point is at the edge of the pattern. Remember to also copy any notches onto the line and transfer them back to the new seam allowance afterwards.
Before you start
Go from the largest alterations to the smallest: First, alter the lengths of the pattern, then, if necessary, the width of the bust, waist, and hips. Sew together a toile/muslin to see whether any refinements to the pattern are still needed.
Bear in mind that if your garment is symmetrical, usually you will work on altering a half or, one fourth of its width. For example, the front pattern piece just represents half of the front, and its width will be doubled when cut out on double thickness. If, for example, you want to add 2 cm (3/4”) of ease at the bust, increase the front pattern piece by 1 cm (3/8”). Whilst if you add 2 cm (3/4”) to the waist circumference, you can add 0.5 cm (1/4”) to the front piece and another 0.5 cm (1/4”) to the back piece, because the alteration is now repeated four times.
Remember to always carry out changes to all pieces the pattern alteration affects, for example any pocket facings, pocket bags, waist bands or similar. If your garment features a lining, make sure to alter not just the shell but also the lining parts, so that all the pieces fit together. Also check whether the alteration affects the size or positioning of individual details and alter the size, shape and location of individual details as necessary, so that they look good, and so that, for example, the slits and zips are long enough to allow the garment to be put on and taken off. Also take into consideration that sometimes the measurements of the zip should be left unchanged so that you can use a standard-length zip without having to shorten it.
Lengthening and shortening
In order to determine how much you might need to alter the pattern lengths, compare your own length measurements to those of the size you have chosen. Lengthen or shorten the pattern only at the points where the length measurements differ, to correspond to the differences between the two sets of measurements at those points. Check out our size chart and learn to take your own measurements here.
Lengthening and shortening line
Start by drawing a lengthening or shortening line: Draw the line between the two body lines, perpendicular to the grain line. On the back piece of trousers, draw the line parallel to the hip line. Always draw the lines at the same height on the front and back pieces:
- Back length: Draw the line between the bust and waist (A). If the difference from the size chart measurement is more than 3 cm (1 1/4”), you can, if you wish, draw another line above the bust, above the armhole notches (B), and divide the alteration evenly between the lines. If you are doing this, remember to draw the line to the sleeve cap, if present in the pattern, at the same height.
- Waist-to-hip: Draw a line between the waist and hip lines (A). On the back piece of trousers, draw the line parallel to the hip line (B).
- Arm length: Draw two lines, one between the bicep and elbow lines, and the other between the elbow line and sleeve end. Distribute any difference in the arm length measurement evenly along these lines (A). If the sleeve is short, straight, or narrows or broadens evenly, you can draw just one line instead of two (B).
- Inseam: Draw two lines, one between the thigh and knee lines and one between the knee and leg end (A). Distribute any difference in the inner leg measurement evenly along these lines. If the leg is short, straight, or narrows or broadens evenly, you can draw just one line instead of two (B).
- Side length: Draw two lines, one below the hip line and the other between the first line and hem line (A). Distribute any difference in the side length evenly along these lines. If the skirt is short, straight, or narrows or broadens evenly, you can draw just one line instead of two (B).
Lengthening and shortening
Shorten or lengthen the pattern along the line you have drawn. Always move the patterns vertically up or down. To help, you can draw a guide line onto the pattern, perpendicular to the shortening or lengthening line, before cutting the pieces, ensuring that you make the alteration in the direction of the line.
- Cut the pattern into two pieces along the length alteration line. (A)
- When lengthening, tape the lower pattern piece to the backing paper. Draw a guideline onto the top of the piece, the required distance from the lower piece, and tape the higher piece to this line. (B)
- When shortening, tape the pieces correspondingly so that they are overlapping the necessary amount. (C)
- True the pattern edges by drawing them smooth and measuring that all matching edges are of equal length.
Truing the altered patterns
Altered patterns should always be finalised before adding in the seam allowances, in order to be sure that the pieces are smooth in shape and can still be sewn together.
Truing pattern edges
Draw the outer lines of the altered pattern neatly and smoothly, for example if openings or corners have been formed along these lines during the process.
If you altered the pattern at the dart, redraw the sides of the darts afresh, without any breaks in the dart (A). Neaten up the end of the dart and even out the sides: Tape a piece of paper under the pattern at the end of the dart (B). Fold the dart together along the centre line so that the sides meet, yhen fold the dart in the direction it will be ironed in in the finished piece (C). Hold the pattern tightly in place and draw the seam neatly and smooth at the end of the dart. (D) Cut along the line with a circular cutter, or draw along the line with a roller in order to copy it onto all layers and then open the dart and cut the edge neatly along the line with scissors. (E)
Measure to make sure that the altered seams match up with their opposite pieces and that the notches correspond. Measure the seams just in the altered area, for example from one edge to the other or to the nearest notch. Note that sometimes pieces, such as sleeve caps, feature easing, i.e. the piece is longer than the piece it's supposed to be sewn onto. Take this easing into account when measuring the pieces and ensure you retain the amount of ease stated. In our Post-2020 patterns any such easing and the amount used are always stated in the pattern.
If a piece has shortened or lengthened, first make sure that there are no errors in the pattern that would create differences. If there is a difference of 4 mm, for example, even out the seam by removing 2 mm from one piece and adding 2 mm to the other.
Check that any angles in the pattern are right angles, or otherwise line up with the pieces to be joined to them. If this is not the case, neaten up the angle.
Right angles: Draw the angle onto the piece again at 90 degrees with a ruler, and merge the line neatly with the original line. Place any pieces to be sewn together against each other and check that the line is smooth.
Other angles: Place the pieces to be sewn together against each other and draw a line neatly and smoothly, using a curve ruler, for example.
The markings indicating the locations of individual pattern details, such as pockets, may be moved when making alterations. Copy the new locations for the markings at your discretion, as far as is possible, placing them in the same positions as in the original pattern.
Adding seam allowances
When you have altered and trued your pattern pieces, add the seam allowances to them and move the notches to the edge of the seam allowance. It may be a smart idea to trace the entire finished pattern afresh onto pattern paper, and add the seam allowances then, so that your altered pattern is neat and easy to store for future use.