How many worms for your worm bin?

How we calculate

• Waste (kg / week) = what you enter, otherwise number of people × 1.2 kg.
• Worms (kg) = waste × 2 ÷ 7 (worms eat about half their weight a day). Rounded to 0.01 kg below 0.3 kg, otherwise to 0.1 kg, at least 0.1 kg. Number of worms = kg × 2,000, rounded to the nearest 100, at least 100.
• To start = half the worms, rounded to 50 g, at least 250 g (never more than the total needed).
• Area (cm²) = waste × 2,050, rounded to 100 cm². Side of a square bin = √area rounded to 5 cm; 40 × 40 cm trays = area ÷ 1,600, rounded up.
• Compost per year (kg) = waste × 52 weeks × 0.3, rounded.
• Cold or heat: amount of waste to feed × 0.1 below 5 °C, × 0.3 from 5 to 10 °C, × 0.6 from 10 to 15 °C, × 1 from 15 to 28 °C, × 0.5 above 28 °C.

Example

2 people, waste not weighed, at 18 °C. Waste = 2 × 1.2 = ≈ 2.4 kg / week. Worms = 2.4 × 2 ÷ 7 = 0.69, so ≈ 0.7 kg (about 1,400 worms). To start: 350 g of worms. Area = 2.4 × 2,050 = ≈ 4,900 cm², for example a 70 × 70 cm bin or 4 trays of 40 × 40 cm. Compost: ≈ 37 kg a year.

Sources: ADEME – Agir pour la transition (at least 250 g of worms, 15–25 °C, foods to avoid), vermicomposting guides. These are guidelines: start slowly and add more waste bit by bit.

Frequently asked questions

How many worms for a worm bin?

For 2 people, the calculator gives about 0.7 kg of worms. You can start with half (250 g minimum); the population doubles within a few months.

How much floor space does my bin need?

About 2,000 cm² per 1 kg of waste a week. Stacking trays does not add surface.

What about cold weather?

Below 15 °C worms eat less: the calculator cuts the amount of waste to feed (× 0.6 between 10 and 15 °C, × 0.1 below 5 °C).

What waste should I avoid?

Citrus, garlic, onion, meat, fish, dairy, oil and cooked dishes. Add as much brown cardboard as wet waste.