How to Do a Slash and Spread Adjustment

Want to add volume to just one area of a garment? Learn how to do a slash and spread adjustment to customise fit or change the style of your sewing patterns.

Slash and spread is one of the most versatile pattern adjustment techniques you can learn. It allows you to add volume to just one part of a garment—without affecting the rest. You can use it to improve fit (for example, adding room for your tummy or bum) or to change the style of a garment by making a specific area fuller.

The basic principle is simple: you cut (slash) into the pattern piece, then spread the sections apart to create extra width (or length) exactly where you need it. By using hinges—small uncut sections that keep everything connected—you can control precisely where the volume is added and where the pattern stays the same.

While it’s not so common, you can also use the same technique to reduce volume – slash and overlap, instead of slash and spread.

Before You Start

A couple of things to keep in mind:

• If you need extra room on both the front and back of a garment at the same point, consider grading between sizes instead. This makes the whole garment larger at that area, which is often simpler and gives a more balanced result.
• If you’re doing a large slash and spread adjustment on only the front or back, always make a muslin to check the garment still hangs on your body in a balanced way. Adding significant volume to just one side can sometimes throw things off.
• This technique alters the look of the garment. By adding more fullness all the way to the bottom of the pattern piece, this adjustment makes garments “swing-ier” with a longer hem. If you would prefer not to change the pattern in that way, a more traditional adjustment like a Full Tummy Adjustment or Full Bum Adjustment would be better.

The Basic Technique

Step 1: Identify where on your pattern piece you need extra volume, and draw a set of evenly spaced lines perpendicular to that area. These are your slash lines.

Step 2: Mark your seam allowances at the edges where your slash lines meet the pattern edges—this is where you’ll create hinges.

Step 3: Cut along your slash lines, stopping at the seam allowance. Then snip in from the other side to create a small hinge—a tiny bridge of paper that keeps the pieces connected.

Step 4: Spread the pieces apart by the amount you need to add, keeping your hinges intact. The hinges ensure that the volume is added only where you want it, while the edges of the pattern stay aligned.

Step 5: Trace your new pattern piece, smoothing any lines as needed.

Tip: Don’t panic if you accidentally cut through a hinge! Just tape it back together and snip a new hinge.

Example 1: Adding Tummy Room to a Top

This is a great adjustment if you need more room across your tummy on a top—and it also works brilliantly as a maternity adaptation.

Step 1: On your front pattern piece, draw a horizontal line below the bust line, marking the seam allowance at the side seam (this retains the bust fit, and means you are only adding volume below the bust). Then, add a series of vertical lines going from that line down to the hem.

Step 2: Cut along the horizontal line until you reach the seam allowance, and then snip in at the other side to create a hinge.

Step 3: Cut along the vertical lines from the hem upwards, stopping just before you hit the horizontal line, creating small hinges.

Step 4: This part is a bit tricky! Spread out the lower sections evenly, until you have the fullness you’re after. You may find using small pieces of restickable tape, or pinning the pieces to a board helps. As you spread the pieces, the entire bottom section will also move down a little as you keep the pattern pieces flat—this is good as it’s also adding a little more length for the fabric to go over your tummy.

Step 5: Trace your new pattern piece, evening it out at the hem.

As the side seam has remained the same, no changes are required to the back piece to fit.

Example 2: Adding Room for a Fuller Bum on a Skirt

This is a simplified slash and spread approach if you need a bit more room across your bum on a skirt—without doing a full bum adjustment. To assess if you need a full bum adjustment, review this tutorial.

In this case, the pattern has two back panel pieces, so we’re going to do the adjustment across them both so that the fullness is distributed evenly.

Step 1: Draw in seam allowance at waistline. Draw a series of evenly spaced vertical lines down from the waist to the skirt, roughly every 2 – 3 inches (5 – 7 cm). The lines should follow the overall shape of the piece: the easiest way is to do the first line connecting the middle of the waist to the middle of the hem, and then keep dividing each side until you have the lines done. Finally, draw in a line at the height of the fullest part of your bum.

Step 2: Cut up the vertical lines, stopping at the seam allowance. Snip into the seam allowance from the other side.

Step 3: This part is a bit tricky! Spread out the sections evenly, until you have the fullness or size you’re after at the relevant point – in this case, measure the gaps at the marking (shown in red) to ensure you’ve added enough, noting that it should be half the total you need as the pieces represent half the back skirt. You may find using small pieces of re-stickable tape, or pinning the pieces to a board helps.

Step 4: Trace your new pattern piece, smoothing the hem as needed.

This approach is adding width at the level of your bum, however it isn’t adding length, which you might need. If that is the case, you can instead lower the center back hem by the amount needed, and taper it to zero at the side seam.

Note, if your skirt has a hem facing, that will need to be altered to match the new shape. The easiest way to do this is to create new facings of the same depth, tracing over your new adjusted pattern pieces.

You Did It!

Once you’ve got the hang of slash and spread, you’ll find yourself using it all the time—whether you’re customising fit or just experimenting with different silhouettes. It’s an incredibly powerful technique that puts you in control of your patterns!

Want to dive deeper into fitting? This technique and many more adjustments are covered in detail in Ahead of the Curve, our best-selling book on fitting for curves. And if you’d like in-depth video tutorials that go much deeper, check out Cashmerette Club‘s library of fitting masterclasses.