Set-In Sleeve Calculator

How this works

A set-in sleeve has two phases — and most calculators only do one of them. The taper goes from cuff to underarm: cast on at the cuff, then distribute increases up to the bicep. This calc uses the same smart-distribution math as the decrease distribution calculator to give you two clean cadences instead of "increase every 8.4 rows" — for 126 rows and 15 pairs of increases, that's "every 9 rows × 6, then every 8 rows × 9" which adds up exactly.

The cap is the distinctive set-in part — the curved top that sews into the body's armhole. We use an Elizabeth Zimmermann-style allocation: bind off 5% of the bicep stitches at each underarm, then distribute the remaining decreases across the cap height in a curved pattern — 1/4 of the decreases in the lower third of the cap (gentle start), 1/2 in the middle third (the steep middle that creates the curve), and 1/4 in the upper third (gentle finish). Bind off the last 2 inches' worth of stitches at the top.

Why Zimmermann's curve?

Equal distribution across the cap height would give a straight taper — a cone, not a curve. The curved shape comes from concentrating decreases in the middle, so the cap narrows fast through the middle zone and gently at the edges. This matches the shape of a typical body armhole, which has a sharper inward curve where it meets the shoulder.

The 1/4 + 1/2 + 1/4 allocation is a defensible average. Patterns with very deep necklines, drop shoulders, or unusual armhole curves may benefit from cap adjustment by hand — knit a few inches and check that the cap shape matches the armhole's curve at the same row count, and adjust the decrease cadence in the middle zone if not.

Bottom-up only — for now

This calculator assumes bottom-up construction: cast on at the cuff, work up. Top-down set-in sleeves are structurally different (the cap is picked up around the armhole and decreased down to the cuff), and that's a separate calc we'll add if demand surfaces. Most published set-in sleeve patterns are bottom-up.

Tips

• Swatch in the round in your project's main stitch (or flat if you'll seam). Wash and block the swatch — both stitch and row gauge can change after blocking.
• Measure the body's armhole on the actual body piece — flat, after blocking the body. The cap height must match this exactly or the sleeve won't set in cleanly.
• The 5% underarm bind-off is conservative. For a snugger fit, bind off 1 inch's worth of stitches each side instead (about 6–8% of bicep on most sizes).
• If the calc throws "Cannot fit N pairs in M rows," your gauge or armhole depth doesn't leave room for the required decreases. Increase the armhole depth by 0.5 inches or knit a slightly looser gauge — or revisit your bicep measurement, which may be too generous.
• For raglan sleeves (no cap), use the raglan calculator instead — the construction math is completely different.