How to Sew Denim from Start to Finish

I’ve made a number of trousers in the past using different types of denim. It’s a versatile fabric that can be turned into shirts, dresses, skirts, jeans, jackets, overalls, aprons, and various accessories like bags and hats. It’s also a great option for home textiles like upholstery projects, curtains, and pillows. In this article, I’ll guide you through how to sew denim from start to finish.

Quick summary:

• Denim is prone to shrinking, so make sure you prewash it once or twice to avoid any unfortunate fitting surprises later. 
• Medium to heavy weight denim can easily become too bulky at the seams. You can use a hammer to flatten the extra bulky sections before sewing them.
• Use “Jeans” needles because they’re stronger than “Universal” ones and less likely to snap. Try a size 80/12 for medium weight denim and a 100/16 for heavy weight denim.
• Denim comes in different thicknesses (light, medium and heavy weight) and different fiber contents (stretch denim vs. non-stretch or rigid denim). These properties will greatly affect your sewing project.

Contents list:

• Is denim hard to sew?
• Tips for bulky seams
• Supplies
• Step 1: How to pretreat denim
• Step 2: How to layout pattern pieces and mark denim
• Step 3: How to cut denim fabric
• Step 4: How to sew denim projects
• Step 5: How to hem denim
• Tips for sewing buttonholes on denim
• Can you sew denim by hand? And how
• Does denim need interfacing?
• Does denim grow with use?

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Is denim hard to sew?

Denim is a stable fabric that’s easy to cut, mark, sew and press, which makes denim sewing projects a joy to work on. The main challenge is sewing through thick layers of denim. Your machine may struggle with the bulk. If you’re sewing stretch denim, avoid stretched-out wavy seams by reducing the presser foot pressure, not pulling or pushing the fabric as it goes through the sewing machine, and steaming the seams with an iron afterward.

Denim fabric comes in different weights, ranging from 4 oz per yard to 18 oz. There are some denim fabrics that are lighter and heavier than these weights, but you’ll most often encounter these ones. We can roughly categorize them as follows:

• 4 – 10 oz / 136 – 338 gsm: lightweight denim (think shirts, dresses, blazers, summer trousers)
• 11 – 13 oz / 373 – 441 gsm: medium weight denim (think mid-weight jeans and jackets)
• 14 – 19 oz / 475 – 644 gsm: heavyweight denim (think heavy, rigid jeans and jackets)

The heavier the weight, the more you’ll need to think about bulk reduction. Many domestic sewing machines (especially cheaper and lighter ones) can have a hard time sewing through multiple layers of thick denim.

As it is a twill weave fabric, denim can fray easily. It’s important to correctly finish your seams to ensure the longevity and durability of your finished project. Medium to heavy weight denims have a unique property: After they go through a washing and drying cycle the frayed edges will mat and lock together, preventing too much further fraying from occurring. Lightweight denims can however be prone to more fraying, so extra care is needed when finishing the seams.

Another characteristic to be mindful of is the fiber content of the denim fabric. While non-stretch denim will be made out of 100% cotton, stretch denims can have a small percentage of lycra or elastane in them. Stretch denim fabrics are usually thinner and softer, making them easier to work with. They do, however, require some extra care: Make sure not to pull or stretch your fabric as it is going through the sewing machine, or else you will end up with distorted, stretched-out seams. If you can, reduce the presser foot pressure so your machine doesn’t push down too hard on the fabric and stretch it out. If your seam ends up a little wavy, you can hover your steam iron over it to shrink the elastic back into its original tightness.

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How to deal with bulky / thick seams:

Use a hump jumper

One of the main challenges you’ll face is sewing through uneven thicknesses created by seams, hems, and edges. Imagine your sewing machine going from sewing 2 layers of fabric to 8 layers – that transition point will often cause issues as the presser foot will not be touching the fabric evenly.

To help with this problem, a small tool is needed that will raise the presser foot to be parallel to the thickest part of the fabric. There are designated Hump Jumper tools (sometimes sold under the brand name Jean-A-Ma-Jig) that can help with this issue, but you can also use a sewing machine needle case or even some folded-up paper if you don’t have a Hump Jumper at hand. 

Use a sturdier sewing machine needle

It’s essential to use an appropriate sewing machine needle. Needles that are not strong enough for layers of denim will break. Try a “Jeans” needle in size 80/12 for medium weight denim and a 100/16 for heavy weight denim.

Hammer your seams

Another useful trick is to use a hammer (yes, a regular hammer) to flatten the especially bulky parts of your sewing project. Simply baste the seam into place, give it some strong taps with a hammer to flatten the layers together, and run it through your sewing machine as usual.

Sew slowly when crossing thick bumps

Finally, remember to go slowly over the particularly thick areas. You can also manually turn the hand wheel on harder spots. 

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Supplies needed:

Sewing machine needles:

While you can get away with using “Universal” needles in a medium size range for lightweight denims, when you start using medium to heavy weight denims you’ll want “Jeans” needles. Sewing multiple layers of thick denim on your sewing machine can be dangerous if you’re using the wrong type of needles, as thin needles will violently break off and fly out.

Jeans needles have a much stronger shank than Universal ones, and a sharper point – these properties allow them to pierce through densely woven twills like denim without breaking off in the face of six layers of 12 oz denim. Just like Universal needles, Jeans needles also come in different sizes: try a 80/12 for medium weight denims and a 100/16 for heavy weight denims.

You may also want to look into getting a topstitching needle if you’re planning to use topstitching thread with your denim project. These needles have larger eyes that allow for the thick topstitching thread to go through easily.

Hump Jumper:

As mentioned above, your sewing machine can struggle with sewing over varying thicknesses of fabric. Raising the back of the presser feet to be level with the thickest parts is a great way to achieve more even stitches. A Hump Jumper is used just for that purpose, but you can also use some folded-up paper in its absence. 

Hardware:

Adding some additional hardware on your denim projects is a great way to make them look more polished and professional. Try using a metal jeans zipper instead of a plastic one, experiment with rivets, and go for a metal jeans button instead of a regular sewn button. 

Thread for sewing with denim:

I like to use all-purpose polyester thread for the construction seams on my denim projects, I find it strong enough while being really easy to sew with.

The topstitching, however, requires some more thought. A single strand of all-purpose sewing thread doesn’t stand out on thick denim fabric. You can either double up your regular thread, use regular thread with a lightning / stretch stitch, use a topstitching weight thread, or – my personal favorite – use a heavy-duty thread. I love using Gütermann’s Extra Strong line for topstitching purposes because it’s much easier on my sewing machine than regular topstitching thread, while still being thick enough to create beautiful, strong stitches on my denim fabric. Gütermann’s Denim thread is another great option for both construction and decorative stitches. 

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Step 1: How to pretreat denim

• Denim fabric is prone to shrinking in the wash, so it is absolutely necessary to prewash it before cutting it. I like to wash my denim fabrics in 40C / 104F water with detergent and softener to simulate how the finished garment will be washed.
• You can also consider prewashing your denim twice to make sure you get all the shrinkage out of the way before cutting your fabric.
• Make sure you press your fabric to remove any creases before placing your pattern pieces down and cutting.
• Denim is also prone to fading in the wash and with wear. I personally like a worn-in, faded look to my denim garments, so I encourage the process of fading by washing my denim fabric and garments in hot water. If you want to keep your denim in its true color for longer, consider washing it at a cooler temperature.

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Step 2: How to layout pattern pieces and mark denim

• For non-stretch denim, simply place your pattern pieces so that the grainline is running parallel to the selvage (or the finished edge) of the denim. 
• For stretch denim, make sure that the direction of greatest stretch (DOGS for short) goes perpendicular to the grainline of the pattern pieces. This means that the garment should stretch horizontally on your body so that you can properly benefit from the stretchy properties of the fabric.  
• I like to mark my denim using some tailor’s soap because it leaves really clear lines on darker-coloured denim. I recommend using chalk or soap based marking tools for darker denim fabric, and using ink-based marking tools for light washes. 

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Step 3: How to cut denim fabric

• I prefer to use my fabric shears to cut denim fabric. It’s important to use sharp, strong shears when cutting denim on the heavier side. 
• You can also use a rotary cutter with a fresh sharp blade if you prefer using them over shears.  

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Step 4: How to sew denim projects

Machine stitching denim: 

Tension:

You may need to adjust the tension settings of your machine when sewing denim, especially denim that’s on the heavier side. Both for all-purpose and topstitching thread, a higher tension may be needed in order to get your stitches looking right on both sides. This will differ by machine, but start with a 5 and sew test stitches on a scrap of your project fabric (4 is generally the standard tension, so 5 is a little higher). If the stitches don’t look straight and defined on the front and back, keep increasing the tension.

Stitch lengths:

I use a stitch length of 2.5 mm for light and medium weight denims, and a length of 3 mm for heavy weight denims. For the decorative top stitching, I use a length of 3.5 to 4 mm as it allows the stitches to pop on the fabric.

Tip for contrast stitching:

I discovered a neat little trick for achieving beautiful, high-contrast topstitching on denims and other heavy twills and canvases a while ago: I match my bobbin thread (which is loaded with regular all-purpose thread) to the color of my fabric, and use a contrasting color thread in a heavier weight on the top. You may need to make your tension a little higher, but once you get the balance right this results in stitches that almost look like handsewn saddle stitches.

Seam types and finishes: 

Flat felled seams:

Flat felled seams are sewn by:

1. Sewing the two pieces of fabric with a 1.6cm / ⅝” seam allowance,
2. trimming one side to half its width,
3. wrapping the other side of the seam allowance around the trimmed side,
4. and topstitching it into place.

It’s extremely durable and only 3 layers thick, making it ideal for all weights of denim. It works especially well for medium to heavy weight denims as it’s flat, strong, and not too bulky. You will often find flat felled seams in your jeans and denim jackets.

Serging / Overlocking:

Using a serger (aka. overlocker) is another great option for finishing your seams. You can choose to serge the pieces separately and press them open after sewing them (= less bulk), or sew the seam first and serge the sewn layers together (= faster, neater). This is another technique you will often see in ready-to-wear denim garments, as it’s a quick and easy method that produces minimal bulk. If you don’t have access to a serger, you can also try running a zigzag stitch along the cut edge of your fabric to reduce the fraying. 

Faux flat felled seams:

You can combine the previous two methods to create a hybrid seam finish called faux flat felled seams. To accomplish this, simply:

1. Sew your pieces with the right sides facing each other,
2. serge the edge,
3. press it to one side,
4. and topstitch it into place.

This method produces less bulk than a true flat felled seam while maintaining its aesthetics and comfort. I love using it on my workwear-inspired trousers and jeans.

Bias bound & Hong-Kong seams:

You can use bias tape to finish your seam allowances for a decorative look on the inside of your garment, and a really durable finish. Seam finishes that use binding are great for unlined garments or heavy-weight denim projects. I like using a light to medium weight cotton bias tape to achieve a really clean result on my denim projects.

French seams:

1. French seams are made by sewing the pieces wrong sides together,
2. trimming the seam allowance,
3. and sewing another line of stitches with the right sides facing.

While it creates a beautiful, strong, completely enclosed seam, it’s a bulky method that’s not ideal for medium or heavy weight denims. You can, however, use it successfully on really lightweight denims that are used for shirts and dresses. 

Pinking shears:

Pinking shears have zigzag shaped blades that reduce fraying. I haven’t had the best luck with using them on denim, but you may be able to use a sharp, high-quality pair on light to medium weight denims. The finish they create isn’t as durable as some of the other options we went through here, so they wouldn’t be my first recommendation. 

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Step 5: How to hem denim

Frayed / raw hem:

The simplest possible way to “hem” your denim project is to skip the hemming! Frayed and distressed hems have been really popular in the last few years, as they give the garment a relaxed, effortless look. Remember to sew a line of straight stitches 1 cm / ⅜” away from the cut edge of your fabric before tossing your finished piece in the washer and dryer. This line of stitching will prevent the fraying from climbing up too high on your garment.

Single turn hem:

Another simple way to hem your denim projects is to finish the cut edge with a serger (aka. overlocker), some zigzag stitches, or bias binding, then fold your hem allowance up and stitch it into place. It creates minimal bulk, so it’s a great option if you’re worried about your sewing machine’s strength. 

Double turn hem:

You can fold your hem allowance up and turn the cut edge under, creating a double-turn hem. This is a bulkier but classic technique that you will see in most of your ready-to-wear jeans. 

Pressing denim:

Denim fabric is really easy to press at all weights. It can handle pretty strong heat and steam, I personally use the cotton setting of my iron with lots of steam to press denim. Depending on the color and finish of your denim fabric, it can get shiny marks on its surface when pressed with a really hot iron, so you may want to use a pressing cloth when pressing it from the right side. 

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Tips for sewing buttonholes on denim:

A lot of domestic sewing machines have a hard time sewing buttonholes on thick denim due to the varying thicknesses of fabric going under the presser foot. If your machine has an automatic 1-step buttonhole function that’s struggling, try creating your buttonhole manually using a tight and short zigzag stitch. You can also try sewing them by hand for a beautiful, professional-looking finish.

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Can you sew denim by hand?

You can sew denim by hand if you don’t have access to a sewing machine. Keruk Jeans sews their jeans entirely by hand, so you know it’s possible.

How to sew denim by hand

It’s essential to have the right equipment so that you have a comfortable experience: use a really sharp needle that’s on the longer side, wear a thimble to protect your finger, and condition your thread so it’s as strong as possible. I like to run all-purpose polyester thread through some beeswax and then press it with a hot iron to melt the wax onto the thread, coating the thread in wax. You can also use some waxed linen thread, especially for the decorative top stitches. 

Even if you have a sewing machine, you may choose to sew certain parts by hand such as sewing on patches, hemming your jeans, or repairing holes. 

Sewing patches onto denim:

Sewing patches onto your denim garments is a fun way to cover up any stains or imperfections while customizing the piece. To do so, simply:

1. Baste the patch into place using some loose basting stitches or tack it on the fabric using some double-sided fusible interfacing.
2. Using a sharp long needle and a thimble, make some running stitches along the edge of your patch to secure it into place. You can also use a variety of decorative embroidery stitches to sew the patch on if you’re feeling more adventurous.

Hemming jeans by hand:

Hemming jeans by hand is a great option as it allows you to keep the original hem of the jeans.

1. Fold the hem up (right sides facing) in the desired amount
2. Do a back stitch or a running back stitch along the fold line of the original hem.
3. Tack the folded-up section along the inseam and the side seam and you’ll have a quick and easy hem that is true to the original. Here’s a video that shows this process in more detail.

Fixing holes:

If you have a hole in your denim garment, you can place a small patch of denim (or a fun contrasting fabric) under the hole and sew it into place using a decorative stitch and some embroidery thread. If you’re after a more subtle finish, try matching the color of the denim as closely as possible and sew it into place using all-purpose thread in a matching color. Sew short running stitches covering the surface area of the patch.

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Quick Q&A’s about denim:

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Does denim need interfacing?

This really depends on the weight of the denim and your personal preferences. Lightweight denims will greatly benefit from some interfacing, especially in areas like collars, cuffs, plackets, waistbands, belts, and so on. For medium to heavy weight denims, interfacing isn’t as crucial. I personally like to throw in some lightweight interfacing to the waistbands of my denim trousers for extra reinforcement, but if you prefer a softer finish to your garment you can also skip it. 

Does denim grow with use?

Rigid (non-stretch) denims tend to relax and grow as you wear them, but they return to their original tightness and size when washed in warm to hot water. If you want to make a close-fitting pair of jeans, I suggest being conservative with the amount of ease you add to the waist and the hips as these areas will loosen up after a few hours of wear.

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What to read next:

• How to Sew Linen from Start to Finish
• How to Sew Wool Fabric from Start to Finish
• How to Sew Silk: the Complete Guide

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This article was written by Nisan Aktürk and edited by Sara Maker.

Nisan Aktürk (author)
Nisan started her sewing journey in December 2019 and already has a fully handmade wardrobe. She’s made 50+ trousers, 20+ buttoned shirts, and a wide array of coats, jackets, t-shirts, and jeans. She’s currently studying for her Sociology Master’s degree and is writing a thesis about sewing. So she spends a lot of her time either sewing or thinking/writing about sewing! Read more…

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Sources:

• https://www.dalstonmillfabrics.co.uk/fabric-blog/denim-weight-conversion-oz-to-gsm
• https://denimhunters.com/denim-wiki/denim-explained/denim-weight/
• https://consumer.guetermann.com/en/products/extra-strong-m-782/
• https://consumer.guetermann.com/en/products/denim/
• https://www.instagram.com/kerukjeans/?hl=en
• https://www.youtube.com/watch?v=ALSay5Tke7g