Worm Bin Size Calculator
Calculate the right vermicomposting bin size and worm quantity based on your household food waste output.
Vermicomposting uses worms (typically red wigglers, Eisenia fetida) to convert kitchen scraps into nutrient-rich worm castings — one of the best natural fertilizers available. Sizing your worm bin correctly ensures the worms can process your food waste without creating odors or attracting pests.
The Basic Rule:
Worms consume roughly half their body weight in food per day.
1 pound of worms (approximately 1,000 worms) processes about 3.5 lbs of food waste per week.
Bin Size Formula:
Bin surface area (sq ft) = Pounds of food waste per week / 1
The depth of bedding should be 8–12 inches (20–30 cm). Worms are surface feeders and do not need deep bins — surface area matters more than depth.
Household Food Waste Estimates:
| Household Size | Estimated Food Waste/Week | Worms Needed | Bin Size |
|---|---|---|---|
| 1 person | 2–3 lbs (1–1.4 kg) | ~1 lb (500 g) | 2–3 sq ft |
| 2 people | 4–6 lbs (1.8–2.7 kg) | ~2 lbs (1 kg) | 4–6 sq ft |
| 3–4 people | 6–10 lbs (2.7–4.5 kg) | ~3 lbs (1.4 kg) | 6–10 sq ft |
| 5+ people | 10–14 lbs (4.5–6.4 kg) | ~4 lbs (1.8 kg) | 10–14 sq ft |
Common Bin Sizes:
| Bin Type | Dimensions | Surface Area | Capacity |
|---|---|---|---|
| Small (under sink) | 18" × 12" × 8" | 1.5 sq ft | 1 person |
| Standard (Rubbermaid) | 24" × 16" × 12" | 2.7 sq ft | 1–2 people |
| Large tote | 32" × 20" × 12" | 4.4 sq ft | 2–3 people |
| Stacking system (Worm Factory) | 16" × 16" × multi-tray | 5+ sq ft | 2–4 people |
| Outdoor flow-through | 24" × 48" × 24" | 8 sq ft | 4+ people |
What Worms Eat vs. Avoid:
| Feed Worms (Green) | Feed Worms (Brown) | Never Feed |
|---|---|---|
| Fruit scraps | Shredded newspaper | Meat / Fish |
| Vegetable scraps | Cardboard (torn up) | Dairy products |
| Coffee grounds + filters | Dried leaves | Oily / Greasy food |
| Tea bags (no staples) | Straw | Citrus (small amounts OK) |
| Crushed eggshells | Coconut coir | Onions / Garlic (small OK) |
Ideal Conditions:
- Temperature: 55–77°F (13–25°C). Worms are most active at 60–70°F (15–21°C). They will die below 40°F (4°C) or above 90°F (32°C).
- Moisture: Bedding should feel like a wrung-out sponge — moist but not dripping. About 60–80% moisture.
- pH: Slightly acidic to neutral (6.0–7.0). Crushed eggshells help buffer acidity from fruit scraps.
- Darkness: Worms avoid light. Keep the bin covered.
Carbon-to-Nitrogen Ratio: For best results, maintain a ratio of about 3:1 brown materials (carbon) to green materials (nitrogen) by volume. This prevents odors and provides balanced nutrition for the worms.
Harvesting Timeline: Worm castings are ready to harvest in 3–6 months. The material will look dark, crumbly, and earthy with no recognizable food scraps. Separate worms from castings using the light method (pile castings in light — worms burrow away from light within 20 minutes) or the side-feeding method (feed only one side of the bin for 2 weeks, then harvest the other side).
Starting Your Bin: Order red wigglers from a reputable supplier. Start with 1 lb of worms for a new bin and let the population grow. Worms double their population every 3–4 months under good conditions. Prepare bedding first: fill the bin with moistened shredded newspaper or coconut coir, then add worms and a small amount of food.