Set-In Sleeve Calculator — Sleeve Cap Shaping

A standard set-in sleeve cap is approximately 60-70% of the armhole depth. For a 20cm armhole, the cap would be 12-14cm tall. A taller cap gives a fitted look; a shallower cap gives more ease of movement.

Bind off the same number of stitches as the body armhole at each side (the underarm bind-off). Then decrease 1 stitch each side in two phases — gently every other (RS) row up the lower cap, then more steeply every row approaching the top — so the decreases form a bell curve over the full cap height. Finally, bind off the remaining stitches straight across the top. The flat top should measure roughly a quarter of the upper arm width (upper arm ÷ 4 − 0.5cm), not a wide square shoulder.

The cap perimeter must match the armhole perimeter. If the cap is too big, decrease more aggressively. If too small, decrease more slowly. A small amount of ease (1-2cm extra) is normal.

Set-in sleeves have a shaped cap that fits into a curved armhole, giving a tailored look. Raglan sleeves use diagonal decrease lines from underarm to neck. Set-in sleeves require more shaping but give a classic, fitted shoulder.

Pin the cap into the armhole at shoulder, underarm, and midpoints. Ease any extra fullness evenly. A small amount of ease creates the rounded shoulder shape. Steam blocking helps settle the ease.