Worm Bin Calculator

How it works

bin floor area = 1 sq ft per lb of scraps a week (≈ 0.2 m² per kg) · worms = scraps per week ÷ 2 (at least 1 lb / 0.45 kg) · about 1,000 red wigglers per lb

Composting worms live in the top layer of bedding, so a worm bin is sized by its floor area, not its volume. NC State Extension and Mary Appelhof’s classic rule is one square foot of surface for each pound of food scraps produced per week (about 0.2 m² per kg), with a bin 8–20″ (20–45 cm) deep. One pound of red wigglers (Eisenia fetida, about 1,000 worms) eats up to two pounds of scraps a week, and the population doubles in a few months if conditions are good. Fill the bin with moist shredded paper or cardboard bedding — damp like a wrung-out sponge.

Worked example

A household making 3.5 kg (7.7 lb) of scraps a week needs 7.7 sq ft of bin floor, 0.72 m² — about 120 × 60 cm. Start with 3.5 ÷ 2 = 1.8 kg of red wigglers (about 3,858 worms) and fill the 30 cm deep bin with about 215 L of moist bedding; the first compost is ready in 3–4 months.

Sources: NC State Extension — Worms can recycle your garbage · UConn Soil Testing — Vermicomposting

Frequently asked questions