Natural Dye Mordant Calculator

Free calculators for mordanting fiber before natural dyeing — alum, tannin, and iron doses by weight of fiber (WOF), for both protein fibers (wool, silk) and cellulose fibers (cotton, linen). Runs entirely in your browser.

Mordant calculator (alum + tannin)

Enter your fiber weight and type to get the alum dose, the required tannin + soda-ash pre-mordant steps for cellulose fibers, and water bath volumes.

Iron modifier calculator

Calculate the ferrous sulfate dose for saddening/darkening color after dyeing, with a fiber-damage risk warning above the conservative default.

Mordant reference chart

Sourced WOF% ranges and water ratios by fiber type and mordant, with citations.