Wool Dyeing Calculator: Calculate Mordant and Dye Quantities for Acid and Natural Dyeing

Dyeing wool is both science and art. Getting the colours you want consistently requires accurate quantities of mordant and dye relative to the weight of fibre — a ratio known as Weight of Fibre (WOF). The Wool Dyeing Calculator takes your fibre weight and target colour depth and calculates exact amounts of mordant and dye so you can work confidently and achieve repeatable results.

Two dyeing methods are supported. Acid dyeing uses synthetic acid dyes with alum or chrome mordanting for bright, wash-fast colours. Natural dyeing uses plant-based dyes — onion skin, weld, woad, madder — with alum or iron mordanting for more muted, earthy tones.

Mordant quantities are calculated as a percentage of WOF: typically 15–20% alum for acid dyeing and 10–15% for natural dyeing. Dye quantities are calculated separately for both light and medium shades. Water volume recommendations are included to ensure adequate dye liquor for even coverage.

Mordant and dye percentages follow Jenny Dean's Wild Colour and Jill Goodwin's A Dyer's Manual, which are the standard UK references for both natural and synthetic wool dyeing. Alum mordant rates follow the recommendation of 15% WOF for alum sulphate (potassium aluminium sulphate), which gives good colour take-up without felting the fibre.

Weigh your dry fibre before wetting. Enter the weight in grams. Select your dyeing method (acid or natural) and your mordant. Select your target shade (light, medium, or dark). The calculator returns mordant weight, dye weight, and water volume in litres for your dye bath. Always mordant the fibre before dyeing for best results, and use separate pots for mordanting and dyeing.