Fabric Dye Calculator: Percent of Fabric Weight

Fabric dyeing by GSM

GSM (grams per square meter) is how fabric weight gets measured. A basic T-shirt lands around 140–180 GSM, a heavyweight tee runs 200–280 GSM, and the really thick premium stuff climbs past 320+ GSM. When you dye by immersion, you dose the dye against the dry weight of the fabric (DOS, or depth of shade). Medium shades usually want 1–3% of fabric weight; a deep black can take up to 6%. You also add salt or mordant fixative at 5–10% of the fabric weight, and you want a water volume of 20–30× the fabric weight so the cloth can move around freely. Say you have 300 g of fabric at 2% dye: that works out to 6 g of dye in 6–9 L of water.

Applications

This comes up in tie-dye, custom dye-on-demand work, the textile industry, fashion overdyeing, and sustainable dyeing with natural pigments like indigo, turmeric, hibiscus and avocado pits. It's handy for upcycling too, and for bringing faded garments back to life.

FAQ

Why use percentage of fabric weight? What the fiber actually absorbs depends on how much fiber there is, not on how much water you used. Working in percentages means the recipe holds up whether you're dyeing a single shirt or a whole batch.

Does it work the same on cotton, linen and polyester? No. Each fiber needs its own class of dye (reactive for cotton, disperse for polyester) and its own fixation conditions.

What is the salt for? Salt pushes the dye into the fiber, a process called exhaustion. With reactive dyes on cotton, soda ash goes in as well to act as the alkaline fixative.