Wool Felting Shrinkage Calculator
Calculate how much wool fabric or fiber you need before wet felting or fulling, accounting for shrinkage rates by fiber type and felting method.
Wool felting is the process of matting and compressing wool fibers using heat, moisture, and agitation. The fibers have microscopic scales that lock together when agitated in warm, soapy water — permanently shrinking the fabric.
Shrinkage rates by fiber and method:
| Fiber / Method | Width Shrinkage | Length Shrinkage |
|---|---|---|
| Merino (100%) — wet felt | 30–40% | 30–40% |
| Corriedale — wet felt | 25–35% | 25–35% |
| BFL (Blue-Faced Leicester) | 20–30% | 20–30% |
| Woven wool fabric — fulling | 15–25% | 15–25% |
| Knitted wool — felting | 25–40% | 35–45% |
| Roving (loose fiber) | 35–45% | 35–45% |
The formula:
If you want a finished piece of 30 × 40 cm and expect 30% shrinkage:
Starting size = Finished size ÷ (1 - shrinkage rate)
Starting width = 30 ÷ (1 - 0.30) = 30 ÷ 0.70 = 42.9 cm
Factors that increase shrinkage:
- Higher water temperature — hotter = more felting (up to boiling)
- More agitation — rubbing harder and longer shrinks more
- Longer felting time — more time = more shrinkage
- Higher percentage of merino — finer micron count felts more aggressively
- Acidic pH — vinegar rinses can increase felting speed
Factors that reduce shrinkage:
- Superwash treated wool — chemically treated to resist felting (will not felt at all)
- Acrylic or synthetic content — synthetics don’t felt, reducing overall shrinkage
- Gentle / cool washing — cool water with minimal agitation = minimal felting
- Wool batting vs roving — pre-processed batting shrinks more predictably
Testing before full project:
Always make a swatch first. Felt a 15×15 cm sample, measure after drying, and calculate your actual shrinkage rate. Every dye lot, every fleece, and every room temperature behaves differently.
Thickness change:
As the fabric shrinks in length and width, it gets thicker and denser. A piece that shrinks 35% in each direction may become 3–4× as thick as the original loose fiber layer. Plan for this when calculating how many fiber layers to lay out for your project.