A vermicompost bin calculator helps you determine the right worm stocking rate, minimum bin surface area, and suggested dimensions based on your weekly food waste output. Red wigglers process roughly 50% of their body weight in food per day — size your bin wrong and worms will either starve or get overcrowded.
Your Food Waste
Worm Species
Bin Type
Recommended Setup
About Your Bin Type
Bin Sizing Reference
How to Use the Vermicompost Bin Calculator
Setting up a vermicompost bin the right size saves you from the most common beginner mistakes: overfeeding (causes anaerobic rot and pests) or underfeeding (worms escape or die from competition). This calculator matches your actual food waste output to the right worm population and bin dimensions.
Step 1: Estimate Your Weekly Food Waste
Use the slider to enter your household's average weekly food scraps — vegetable trimmings, fruit peels, coffee grounds, eggshells, plain paper and cardboard. The average 2-person household generates 1.5-2.5 lbs (0.7-1.1 kg) of worm-suitable scraps per week. Meat, dairy, and oily foods are excluded.
Step 2: Choose Worm Species
Red wigglers (Eisenia fetida) are the standard choice — they're surface dwellers that thrive in the top layer of decomposing organic matter, making them perfectly adapted to bin composting. European nightcrawlers are larger and make better fishing bait but process food more slowly; you'll need more worms by weight for the same food waste.
Step 3: Select Bin Type
A basic plastic tote (20-30 gallon Rubbermaid with drainage holes drilled in the bottom) works perfectly for small setups. Stacking tray systems allow expansion by adding trays as the population grows — when the bottom tray is full, worms migrate upward through food placement. Flow-through bins have a mesh bottom through which finished castings are harvested without disturbing the worm population.
Step 4: Read Your Results
The calculator gives you the minimum bin surface area (in sq ft or sq cm), suggested dimensions, recommended worm weight, and estimated cost to purchase that quantity of worms. Toggle between imperial and metric units using the switch at the top. Bin depth of 8-10 inches (20-25 cm) is optimal — worms process the top 6 inches; deeper bins require more bedding without adding processing capacity.
Starting and Maintaining Your Bin
Start with moistened bedding (shredded cardboard and newspaper works well) to about 6 inches depth. Add worms and wait 1 week before adding food — this lets them settle in. Start with small food additions in one corner, then rotate feeding spots. Healthy worm bins smell like fresh earth; any bad odor means the bin is too wet or has been overfed. Finished vermicompost takes 2-3 months and looks like dark, crumbly, earthy-smelling soil.
Frequently Asked Questions
Is this vermicompost calculator free?
Yes, completely free with no signup. All calculations run locally in your browser.
How much can red wigglers eat per day?
Red wigglers (Eisenia fetida) can consume approximately 50% of their body weight in food scraps per day under optimal conditions. In practice, home bins typically process 25-35% of worm weight daily due to temperature variation and bedding consumption.
How much space do worms need?
The general rule is 1 lb of worms per 1 square foot of bin surface area. This gives worms room to move, prevents overheating, and ensures adequate oxygen throughout the bin. Depth should be 8-12 inches — worms work in the top 6 inches, so deeper bins waste space.
What type of bin is best for beginners?
A basic plastic storage bin with drainage holes works well for beginners. Stacking tray systems (like Worm Factory or UrBin) make harvesting easier as you add more trays when the bottom is colonized. Flow-through systems (continuous flow bins) produce the cleanest vermicompost with minimal disturbance to the worm population.
How long does it take to get usable vermicompost?
With a healthy bin and regular feeding, you can harvest vermicompost in 2-3 months. The bin needs time for food to break down and for worms to process the material into castings. Finished vermicompost looks like dark, crumbly, earthy-smelling soil — not recognizable food waste.
Where do I buy red wigglers?
Red wigglers (Eisenia fetida) are sold online and at some garden centers. Typical pricing is $30-45 per pound plus shipping. Local vermiculture Facebook groups often offer cheaper starter cultures. Most beginners start with 1 lb of worms.
What should I not put in a worm bin?
Avoid: meat, fish, dairy, oily or greasy foods (attract pests), citrus and onions in large quantities (acidic, disliked by worms), pet waste, diseased plants. Worms process: fruit and vegetable scraps, coffee grounds, tea bags, eggshells, plain paper and cardboard (great bedding).