Blocked vs Unblocked Calculator — Size Change After Blocking

On a flat wet block, superwash wool grows the most — descaling and the polymer coating let it stretch noticeably (around 8-15%). Untreated wool changes only a little, typically up to about 5-6%. Alpaca actually changes the least on a flat block, but because its fibres are smooth it keeps stretching under its own weight and will not shrink back, so an alpaca garment grows over wear and when dried hanging. Cotton and linen can shrink slightly. Acrylic barely changes with wet blocking but responds to steam. Always block your gauge swatch to know exactly how your specific yarn behaves.

Yes. If you know your yarn grows 10% after blocking, you should knit your piece to be about 10% smaller than the target finished size. Alternatively, match your gauge on a blocked swatch so the pattern measurements will work without further adjustment.

Wet blocking: soak in lukewarm water for 20 minutes, gently squeeze out water (never wring), roll in a towel, then pin to shape on blocking mats. Steam blocking: hold a steam iron above the fabric without touching it. Spray blocking: mist with water and pin to shape. Different fibres respond best to different methods.