The thumb gusset is the easiest way to add a thumb to a mitten
A mitten thumb is almost always made using a gusset—a wedge-shaped section you knit into the palm as you work the hand, then pick up and finish separately. You don't knit the thumb as a separate piece and sew it on. Instead, you increase stitches on either side of a center line while knitting the palm, creating a triangular space. When the gusset is large enough, you bind off those stitches, pick up the live stitches around the opening, and knit the thumb tube downward.
This method works because the gusset sits naturally where your thumb joins your hand, and the picked-up stitches follow the shape of the opening you've created. The result is a thumb that doesn't pull or gap, and you avoid the seaming that comes with other methods.
Key Takeaways
- A gusset is a triangular section of increases you knit into the palm while making the hand, creating space for the thumb opening.
- You increase one stitch on each side of a center stitch at regular intervals—usually every other round—until the gusset is wide enough.
- Once the gusset reaches the right size, you bind off those stitches and pick up new stitches around the opening to knit the thumb tube.
- The thumb is knitted downward from the hand, not upward, so you work from the wrist end of the thumb toward the fingertip.
- Measuring your own hand or the intended wearer's hand before you start ensures the thumb sits in the right place and is the right length.
Where to place the gusset on your mitten
The gusset should sit on the palm side of the mitten, roughly where your thumb naturally sits when your hand is relaxed. On a typical adult mitten, this is about one-third of the way around the circumference from the pinky side, or roughly at the side seam if you were sewing a mitten.
Most patterns place the gusset between the index and middle fingers. If you're knitting in the round on circular needles or double-pointed needles, you'll mark the center stitch of the gusset with a stitch marker. This center stitch stays constant throughout; you increase on the stitch when ready before it and when ready after it.
Before you cast on, measure the hand you're knitting for. Wrap a soft measuring tape around the palm at its widest point, just below the knuckles. A child's mitten is usually 6 to 7 inches around; an adult's is 8 to 9 inches. This measurement tells you how many stitches to cast on and helps you figure out where the gusset should start.
How to increase for the gusset
The standard increase method for a gusset is the make-one increase (M1), worked on both sides of the center stitch. A make-one is an invisible increase that doesn't create a hole; you lift the horizontal strand between two stitches and knit it through the back loop.
Most patterns tell you to increase every other round, meaning you work one round with no increases, then increase on the next round. This creates a gradual, even slope. If your pattern says "increase every round," you increase on every single round, which makes the gusset grow faster and sit more upright.
The sequence looks like this: knit to one stitch before the center stitch, M1, knit the center stitch, M1, knit to the end of the round. On the next round (or the round after, depending on your pattern), repeat. Each time you increase, the gusset gets two stitches wider—one on each side.
Keep track of how many rounds you've worked since you started the gusset. You'll need this number to know when to stop increasing and bind off.
Knowing when the gusset is large enough
The gusset should be wide enough that when you fold it in half, it covers the space from your wrist to the base of your thumb. For an adult, this is usually 12 to 16 rounds of increases (6 to 8 increase rounds, since you increase every other round). For a child, it's usually 8 to 12 rounds of increases.
A better way to judge is to try the mitten on as you knit. Stop increasing when the gusset reaches the base of your thumb—the point where your thumb naturally bends away from your hand. If you're knitting for someone else, measure from their wrist to that same point and use that measurement to guide you.
Once the gusset is the right size, you'll have a certain number of stitches in the gusset (the center stitch plus all the increases on both sides). Write this number down. You'll bind off all the gusset stitches on the next round, leaving an opening.
Binding off the gusset and picking up for the thumb
On the round after your last increase, knit to the first gusset stitch. Bind off all the gusset stitches using your regular bind-off method (usually knit two, pass the first stitch over the second). When you reach the last gusset stitch, cut the yarn and pull it through to find the bind-off, then rejoin yarn and continue knitting the hand.
You now have an opening where the gusset was. The next step is to pick up stitches around this opening to form the thumb tube. Using a smaller needle (usually one size smaller than your hand needle), pick up one stitch in each bound-off stitch along the bottom of the opening, then pick up one stitch in each stitch along the sides of the gusset where you increased.
The exact number of stitches you pick up depends on the size of the opening, but it's usually between 12 and 20 stitches for an adult mitten. You want the picked-up stitches to form a smooth circle around the opening with no gaps or puckers.
Knitting the thumb tube
Once you've picked up stitches, join them into a round and knit downward toward the fingertip. The thumb is usually knitted in stockinette stitch (knit every round) in the same yarn you used for the hand, unless your pattern specifies otherwise.
Knit straight down without any shaping until the thumb reaches the base of the fingernail on the hand you're measuring. For an adult, this is usually 2 to 2.5 inches; for a child, 1 to 1.5 inches. Then decrease to close the tip: knit two together around the entire round until you have about 4 to 6 stitches left, cut the yarn, thread it through the remaining stitches, and pull tight to close the hole.
Weave in the yarn ends on the inside of the mitten. The thumb should now sit naturally at the side of the hand with no gaps or twists.
Common mistakes and how to avoid them
The most common mistake is increasing too slowly, which makes the gusset too narrow and the thumb opening too small. If your increases are too far apart, the thumb will be cramped or won't fit. Count your rounds carefully and increase on schedule.
Another mistake is placing the gusset too far toward the pinky side or too far toward the index finger. If it's in the wrong spot, the thumb will sit awkwardly when you wear the mitten. Before you start, mark where the gusset center should be with a stitch marker and don't move it.
A third mistake is picking up too many or too few stitches around the opening. If you pick up too many, the thumb will be loose and baggy. If you pick up too few, it will be tight and uncomfortable. Pick up one stitch in each bound-off stitch and one in each increase stitch, and adjust only if there are obvious gaps.
Frequently Asked Questions
Can I knit the thumb upward instead of downward?
Yes, but it's less common. You would knit the thumb upward from the wrist end, which means casting on new stitches at the opening instead of picking them up. This method requires you to graft or bind off the thumb stitches to the hand stitches at the top, which adds an extra step. Downward is simpler because you pick up existing stitches and the join is already find.
What if the gusset stitches don't line up evenly when I bind them off?
This is normal if your increases weren't perfectly centered. Bind off all the gusset stitches anyway—the opening doesn't have to be perfectly symmetrical. When you pick up stitches, you can adjust by picking up slightly more stitches on one side if needed. The picked-up stitches will even out as you knit the thumb.
How do I know if my thumb is the right length?
The thumb should reach to the base of your fingernail when your hand is relaxed. If it's too long, it will bunch up inside the mitten. If it's too short, your thumb will stick out. Measure the intended wearer's thumb from wrist to nail base before you start, and use that as your target length.
Do I have to use make-one increases, or can I use a different increase?
Make-one is the standard because it's invisible and doesn't create holes. You can use yarn-over increases if you want a decorative effect, but they will create small eyelets along the gusset edges. Avoid knit-front-and-back increases because they can create bumps that make the gusset look uneven.