Raglan Yoke & Sweater Ease Calculator
A raglan yoke asks for four things and can only give you three. The underarm cast-on is the slack that makes the sums work.
A raglan yoke asks for four things and can only give you three
A raglan has four seam lines and each increase round puts one increase either side of each, so the body gains 4 stitches a round and each sleeve gains 2 — 8 in all. Simple enough. The trouble is how many things have to come out right at the same time.
The neck has to fit a neck. The body has to reach the chest. The sleeve has to reach the upper arm. And the yoke has to be exactly as deep as the armhole — which fixes the number of increase rounds outright, before you have chosen anything else. That is four conditions and, once the depth has spoken, two free quantities: how the neck splits between body and sleeves.
So it generally does not solve, and the failure is not random. Across seven realistic adult sweaters the chest wanted more increase rounds than the armhole had room for in five, agreed within a round in two, and wanted fewer in none. A 44-inch chest at 5 stitches to the inch wants 33.7 increase rounds and the armhole has space for 29.8.
The underarm cast-on is the slack variable
Those stitches you cast on at each underarm when the sleeves come off join the body without ever having been increased into. That is what reconciles the sums, and it means their number is not a style choice — it is forced:
u = (chest + 2·arm + 4 − neck − 8r) / 4
Three things fall out of that, and they are the practical content of this page.
- Chest and neck pull in exactly opposite directions — the sensitivities are +¼ and −¼ stitch per stitch. Every inch of chest not matched by an inch of neck goes straight into the underarm. Necks barely change across a size run and chests change a lot, which is the arithmetic behind raglans fitting small sizes beautifully and large ones badly.
- Every extra increase round takes two stitches off each underarm. Exactly two. That is the knob to reach for when the number comes out silly.
- A negative answer is a real diagnosis, not an error. It means the yoke reached the chest before the armhole was deep enough, so you would have to cast off. The tool says so rather than clamping it to zero and pretending.
One consequence looks like a bug and is not: the underarm number sometimes drops as you widen the chest. The armhole only admits whole increase rounds, so when the depth crosses a threshold the round count ticks up and the underarm falls by two. The trend is upward; the teeth are the rounding.
Where the plain raglan simply stops working
I expected that grading the neck, arm and armhole sensibly alongside the chest would make every size come out. It does not, and the refutation is the more useful finding: a plain raglan at a constant increase rate has a working window, and under conventional grading at 5 stitches to the inch that window runs from about a 35-inch chest to about 54. It falls off both ends, for two different reasons with two different remedies.
| End | What fails | What to do |
|---|---|---|
| Too small | The yoke reaches the chest before the armhole is deep enough, so the underarm cast-on comes out negative. | Shorten the yoke, or increase less often — every third round instead of every other. |
| Too large | Body and sleeves are fed by the same neck, and the sleeve runs out of stitches to start from. | Widen the neck, deepen the armhole, or add body-only increases below the yoke. |
Across that window the underarm cast-on only ever grows and the sleeve's share of the neck only ever shrinks. That squeeze is the mechanism, and when the sleeve's share reaches zero the construction is finished — not badly fitted, but arithmetically unavailable.
Ease is the decision, not the size
| Ease | Over the bust | |
|---|---|---|
| Negative | -4″ to -1″ | Clings. Needs a stretchy fabric and no shame. |
| Zero | -1″ to +1″ | Follows the body. Unforgiving of gauge error. |
| Classic | +1″ to +3″ | The default for a fitted jumper. |
| Relaxed | +3″ to +6″ | Room for a shirt underneath. |
| Oversized | +6″ to +12″ | A deliberate silhouette, not a fitting error. |
And a reminder of why gauge is not negotiable here: at 5 stitches to the inch on a 40-inch sweater, being half a stitch per inch out moves the finished chest by about 3.6 inches. That is more than the entire gap between two of the bands above, arrived at by accident.
What this models, and what it does not
- A plain top-down raglan at a constant rate. Real patterns depart from this constantly — increasing every round for a while then every other, short rows to raise the back neck, sleeve shaping below the underarm. Those are all ways of buying back the same slack this page accounts for in one number.
- It is a straight-edge, not a pattern. Use it to understand why a pattern does what it does, or to sanity-check a plan before casting on 250 stitches.
- The neck is made exact and the chest absorbs the rounding. A neck a stitch out will not divide by four raglan lines; a chest a stitch out is a fifth of an inch nobody will ever find.
- Back and front are treated as one number. Many patterns give the back a few more stitches than the front. Split the body figure unevenly if yours does.
How to use
- Enter the finished neck, chest, upper arm and armhole depth.
- Add your gauge and how often the pattern increases.
- Read the neck cast-on, the increase rounds and the underarm stitches.
- Check the diagnosis — it says which of the four constraints is binding.
Frequently asked questions
How many stitches do I cast on for a top-down raglan?
The neck circumference times your stitch gauge, split into body, two sleeves and four raglan stitches. What is not obvious is that the split is not free: once the armhole depth has fixed the number of increase rounds, the split is determined by the chest and arm you are aiming at. This tool solves that rather than leaving it to guesswork.
Why does my raglan never come out right?
Because it is over-determined. Four things have to be true at once — neck, chest, arm and armhole depth — and once the depth fixes the increase rounds there are only two quantities left to choose. Across seven realistic adult sweaters the chest wanted more increase rounds than the armhole allowed in five, agreed in two, and wanted fewer in none.
What are the underarm cast-on stitches actually for?
They are the slack variable. Those stitches join the body without ever having been increased into, which is what reconciles the chest against the depth. Their number is forced rather than chosen: u = (chest + 2·arm + 4 − neck − 8r)/4.
Why do raglans fit small sizes better than large ones?
Because chest and neck pull the underarm cast-on in exactly opposite directions, at +¼ and −¼ of a stitch each. Necks barely change across a size run while chests change a lot, so every unmatched inch of chest goes into the underarm. Push it far enough and the sleeve runs out of neck stitches to start from and the construction stops being available at all.
Is there a size beyond which a plain raglan does not work?
Yes, and it surprised me. Even with the neck, arm and armhole all graded sensibly alongside the chest, a constant-rate raglan has a working window — around a 35 to 54 inch chest at 5 stitches to the inch. Below it the underarm cast-on goes negative; above it the sleeve runs out. Designers get past the top end with body-only increases below the yoke, a deeper armhole or a wider neck.
My underarm number went DOWN when I widened the chest. Is that a bug?
No, it is the rounding showing. The armhole only admits whole increase rounds, so when the depth crosses a threshold the round count ticks up by one — and each extra increase round takes exactly two stitches off each underarm. The trend is upward and the teeth are the integer rounding.
What does a negative underarm cast-on mean?
That the yoke reached the chest before the armhole was deep enough, so you would have to cast off rather than on. It is a real diagnosis, not an error: shorten the yoke, or work the increases less often. The tool says so rather than clamping it to zero and giving you a plan that cannot be knitted.
How much ease should a sweater have?
It depends entirely on the silhouette you want, which is why "size medium" means nothing on its own. Roughly: negative ease clings, zero follows the body, one to three inches is a classic fitted jumper, three to six is relaxed, and beyond six is a deliberate oversized look rather than a fitting error.
How much does a gauge error cost on a sweater?
At 5 stitches to the inch on a 40-inch chest, being half a stitch per inch out moves the finished garment by about 3.6 inches. That is more than the whole gap between two ease categories, arrived at by accident. Swatch, wash the swatch, and measure it dry.
Does this replace the pattern?
No. It models a plain top-down raglan increased at a constant rate at four seams. Real patterns depart from that constantly — increasing every round for a while, short rows to raise the back neck, sleeve shaping below the underarm — and all of those are ways of buying back the same slack this accounts for in one number. Use it to understand a pattern, or to sanity-check a plan before casting on 250 stitches.
Does this send anything anywhere?
No. Everything is calculated in your browser and nothing is stored or uploaded.
🔒 This tool runs entirely in your browser. Nothing you enter is uploaded, logged, or stored.