If you've ever knit a pair of mittens and ended up with a thumb that pinches, gapes, or sits at an awkward angle, the fix almost always comes down to one thing: the gusset. A thumb gusset is the small wedge of extra stitches built into the hand of a mitten or glove that gives your thumb room to move without distorting the rest of the piece. It looks fussy in a pattern's instructions, but once you understand the logic behind it, a gusset is just three simple moves repeated in order: mark, increase, and set aside. This tutorial walks through exactly how that works, so you can knit a gusset confidently in any mitten or glove pattern that calls for one — even one you're improvising yourself.
What a Thumb Gusset Actually Does
A thumb sewn on flat, or a straight hole cut into the side of a mitten, forces your hand into an unnatural position. A gusset solves this by gradually growing a triangle of extra stitches out from a single point low on the palm side of the hand. Because the increase happens slowly, over several rounds, the fabric expands smoothly instead of jumping in width all at once. When the triangle is wide enough, those stitches get set aside rather than knit into the rest of the hand, leaving a shaped opening exactly where your thumb needs to come through.
This is different from an "afterthought thumb," where you knit straight through the thumb area and cut it open later for a shorter, straighter thumb with no shaping. A true gusset takes a little more attention but gives a better-fitting result, which is why most mitten and glove patterns beyond beginner level use one.
What You'll Need Before You Start
- A mitten or glove in progress, knit in the round, up to the point your pattern says to begin the thumb gusset (usually an inch or so above the ribbing)
- Removable stitch markers, or scraps of contrasting yarn tied in loops
- A short length of smooth waste yarn or cotton scrap yarn (avoid fuzzy yarn, which grips and is hard to remove later)
- A darning needle for weaving in ends later
If you're following a pattern, it will tell you exactly how many stitches to end up with in your gusset and how many rounds to knit between increases. If you're working out your own numbers, aim for a gusset that ends up roughly 12 to 18 stitches wide for an adult hand, worked over increase rounds spaced two to three rounds apart.
Step 1: Place Your Thumb Marker
Knit the hand of your mitten as usual until you reach the point where the thumb should begin — this is typically right after the ribbing, on the palm side of the hand. At that point, work to the stitch where the center of the gusset will sit, and place a marker before it and another marker right after it, so that single stitch sits between the two markers. That center stitch anchors the whole gusset; everything else grows outward from it.
Right and left mittens mirror each other, so marker placement flips between hands: place the gusset marker near the start of the round for one hand and near the end for the other, so the thumbs land on the correct sides when worn. Jot down which side you used for the first mitten so the second one matches.
Step 2: Increase on Either Side of the Marker
This is the heart of the gusset. On the first increase round, slip the first marker, work an increase, knit the stitch(es) in between, work another increase, then slip the second marker and continue around the rest of the hand as normal. That adds two stitches to the gusset — one on each side of the center stitch — without disturbing the pattern or shaping anywhere else on the mitten.
Choosing an increase
Not every increase looks the same, and a gusset is one place worth being deliberate about it. A left-leaning increase (M1L) on the first side and a right-leaning increase (M1R) on the second will angle neatly toward the center stitch, giving clean, symmetrical edges instead of a lumpy look. If your pattern doesn't specify, this paired approach is a safe default. Some knitters prefer lifted increases instead, since they sit flat and disappear into the fabric — either works well.
How often to repeat
After that first increase round, knit one or two plain rounds with no shaping, then repeat the increase round. Continue alternating plain rounds with increase rounds until you have the total gusset stitch count your pattern calls for, or until the gusset looks about as wide as the base of your own thumb. Each repeat adds two stitches, so if you need a 15-stitch gusset and you're starting from one center stitch, you'll repeat the increase round seven times.
Step 3: Move the Gusset Stitches to Waste Yarn
Once the gusset has reached its full width, you don't knit those stitches into the rest of the hand. Instead, on the next round, when you reach the first marker, remove it and slip all the gusset stitches purlwise onto a length of waste yarn (or a stitch holder, if you prefer). Tie the ends of the waste yarn loosely so the stitches can't slide off, then remove the second marker.
To keep the hand at the correct width, cast on a small number of new stitches — usually two to four — in the gap, typically using a simple backward-loop cast-on. This bridges the opening so you can keep knitting the hand in the round without a hole, and gives you a little extra fabric at the base of the thumb that helps avoid a hole later.
Step 4: Finish Knitting the Hand
With the gusset stitches safely parked and the gap bridged, continue knitting the hand exactly as your pattern directs — working any remaining length, then shaping and closing the top of the mitten as usual. The waste yarn just sits there holding those stitches, out of the way, until you're ready to come back for them.
Step 5: Pick Up and Knit the Thumb
Once the hand is finished, it's time to build the thumb from the stitches you set aside. Carefully slide the held stitches off the waste yarn and onto a double-pointed needle or the needles of your choice for small-circumference knitting, then remove the waste yarn entirely. Next, pick up and knit the stitches along the cast-on edge you added in Step 3 — this closes the gap and joins the thumb into one continuous round.
Closing any gap holes
It's common to end up with a small hole at each corner where the gusset stitches meet the picked-up stitches. Many knitters pick up one extra stitch at each corner beyond what the pattern calls for, then decrease it away on the very next round (knitting it together with its neighbor). This tidies up the corner completely and is much easier than trying to fix a hole after the fact.
From there, knit the thumb in the round — following your pattern, or simply knitting straight until it reaches just past the tip of your own thumb, then shaping the top with evenly spaced decreases every round or two until a few stitches remain, and cinching them closed.
Troubleshooting Common Gusset Issues
Gusset feels too tight or thumb hole is too small: Add one more increase repeat next time, or space increases closer together for a wider gusset over the same number of rounds.
Visible holes where the thumb meets the hand: Make sure you're picking up the corner stitches described above and decreasing them away on the first thumb round, and try picking up stitches through both loops rather than just the front loop for a firmer join.
Thumb sits crooked: Double check your marker placement matched your pattern's row/round count for right versus left hand — a gusset placed even a stitch or two off-center will pull the thumb toward one side.
Increases look messy or uneven: Switch to paired directional increases (M1L and M1R) if you aren't already using them; they're specifically designed to angle cleanly and disappear into the fabric.
A thumb gusset can look intimidating the first time you meet one in a pattern, but it really is just this repeating rhythm: mark the spot, grow it a little at a time, park it, and come back later. Once you've knit one, you'll recognize the pattern instantly in any mitten or glove design — and you'll have full-fingered gloves, half mitts, and mittens with genuinely comfortable, well-shaped thumbs.