Worm Bin Calculator
Weekly food waste to worm count, bin size, and bedding amount.
Average household produces 3-7 lbs of food scraps per week.
This tool is for informational and educational purposes only. It is not a substitute for professional financial, medical, legal, or engineering advice. See Terms of Service.
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Request a ToolHow to Use the Worm Bin Calculator
Vermicomposting (composting with worms) is one of the fastest ways to turn kitchen scraps into rich, dark compost for your garden. Getting the worm-to-food ratio right is the key to a healthy, odor-free bin. Here is how to use this calculator:
- Enter your weekly food waste. Weigh a week's worth of kitchen scraps to get an accurate number, or estimate: the average American household generates 3-7 pounds of food scraps per week. Typical items include vegetable peelings, fruit scraps, coffee grounds, and tea bags. Do not count meat, dairy, or oily foods, which should not go into a worm bin.
- Read your results. The calculator shows the pounds of worms needed, the approximate worm count (1 lb = about 1,000 red wigglers), the bin surface area, the recommended bin size, and the amount of starting bedding material needed.
- Purchase your worms. Red wigglers (Eisenia fetida) are the species used for vermicomposting. They are sold by the pound from worm farms. Do not use nightcrawlers, which are soil dwellers and do not thrive in bins.
Start with slightly more worms than the minimum. A healthy worm population doubles roughly every 90 days, so a small overage corrects itself quickly.
About the Worm Bin Calculator
The core calculation is based on the rule of thumb that red wigglers can consume roughly half their body weight in food per day under good conditions. To handle a given daily food volume, you need twice that weight in worms. For example, if you generate 0.5 lbs of scraps per day (3.5 lbs/week), you need about 1 lb of worms (approximately 1,000 red wigglers).
Bin surface area is calculated at 1 sq ft per lb of worms, which matches the density range worms prefer. Overcrowding stresses worms and slows composting; underpopulation means scraps sit too long before being processed. Bedding (shredded cardboard, newspaper, or coco coir) should fill the bin loosely at a volume roughly equal to the worm mass and weigh 4-6 times the worm weight when dry. Bedding provides carbon to balance the nitrogen in food scraps and keeps the bin from becoming a wet, smelly mess. All calculations run in your browser with no data stored or transmitted.
Frequently Asked Questions
What kind of worms do I need for a worm bin?
Red wigglers (Eisenia fetida), also called red worms or tiger worms, are the species used for vermicomposting. They live near the soil surface and thrive in decomposing organic matter, making them ideal for bins. Do not use common earthworms or nightcrawlers (Lumbricus terrestris), which are soil-dwelling burrowers and will not thrive in the enclosed, surface-level environment of a worm bin. Red wigglers are sold by the pound from worm farms, garden centers, and online suppliers.
What can I put in a worm bin?
Worm bins accept most plant-based food scraps: vegetable and fruit peelings, coffee grounds (including the paper filter), tea bags, crushed eggshells, bread and grains in small amounts, and paper napkins. Avoid meat, fish, dairy, and oily or greasy foods, which smell bad, attract pests, and are too acidic for worms. Also avoid citrus peels and onions in large quantities as their acidity can irritate worms. Cut or shred food scraps into smaller pieces to speed up decomposition.
How long does it take to get compost from a worm bin?
Under good conditions, a healthy worm bin produces finished vermicompost (worm castings) in 3-6 months from startup. After that, you can harvest castings every 2-3 months. The bin temperature should stay between 55-77°F, and moisture should feel like a wrung-out sponge. Harvesting is done by moving finished compost to one side, adding fresh bedding and food to the other, and letting worms migrate to the new food source over 1-2 weeks before removing the finished castings.
Why does my worm bin smell bad?
A healthy worm bin should smell earthy, not foul. Common causes of bad odors include adding too much food too quickly (scraps rot before worms process them), food waste sitting on top without being covered with bedding, too much moisture causing anaerobic conditions, adding meat or dairy products, or insufficient carbon-to-nitrogen balance. To fix a smelly bin: stop adding food temporarily, bury existing scraps under bedding, add dry shredded cardboard to absorb excess moisture, and aerate gently. Once the worms catch up, normal feeding can resume at a slower rate.