Worms breathe through their skin, and that skin has to stay damp for oxygen to pass through. Too dry, and a worm can't breathe properly and will try to escape or burrow deep to find moisture elsewhere. Too wet, and the bin loses oxygen entirely, turning anaerobic, which is where bad smells and dying worms both come from.

Most people manage worm bedding moisture by feel, adding water a little at a time until it seems "about right." That works eventually, but it's slow and easy to overshoot. A moisture calculator gets you to the correct range on the first try instead of guessing your way there.

Even with an exact number, a final physical check helps. Grab a handful of bedding and squeeze it. Properly moistened bedding should feel like a wrung-out sponge: damp all the way through, with no water dripping out. If water runs between your fingers, it's too wet. If it feels dry or crumbly, it needs more.

This calculator assumes your starting bedding is completely dry. Most bagged coco coir already holds some residual moisture, so you may need slightly less water than shown. Add gradually and let the sponge test confirm you've hit the right level.

Weigh your dry bedding before adding water, and enter that number along with whether you're working in pounds or kilograms. Choose your target moisture percentage, or use 70% as the safe default. Hit calculate, and you'll get the exact amount of water to add, shown in both weight and volume.

Add the water gradually, mixing as you go. Bedding absorbs water at different rates depending on the material, and pouring it all in at once can leave dry pockets sitting right next to soggy ones.