Free worm bin size calculator: enter daily food waste, bin length and width and stocking density to get bin area, worms needed and daily capacity.
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Enter your daily food waste in pounds (weigh a week of kitchen scraps and divide by 7 for a fair figure), the length and width of your bin in inches, and a stocking density: 0.5 pounds per square foot if you are a beginner, 1 pound per square foot for a standard bin, or up to 2 pounds per square foot for an experienced vermicomposter. The calculator returns bin surface area, worms needed in pounds and count, daily processing capacity, and the bin area your waste actually needs, so you can see whether your bin keeps up or needs to grow.
Worms live in the top 6 to 8 inches of bedding, so surface area, not depth, decides how many worms a bin holds. A 24 by 24 inch bin has 576 / 144 = 4 square feet of surface, and at 1 pound per square foot it holds 4 pounds of worms, or about 4,000 red wigglers. Those worms eat about half their body weight per day, so the bin processes about 2 pounds of scraps daily. Working backwards, 1 pound of daily waste needs 2 pounds of worms, which at 1 pound per square foot needs 2 square feet of bin surface.
Start with a food waste audit: collect a week of vegetable scraps, weigh them, and divide by 7 for daily waste. Measure the top surface of your bin, since tapered bins are narrower at the bottom and the top is what counts. Pick a stocking density honestly: beginners should use 0.5 pounds per square foot, because new worms sometimes try to leave an unfamiliar bin, while experienced keepers can use 1 pound per square foot and experts up to 2. Compare the daily capacity with your daily waste: if capacity is lower, you need a bigger bin or more worms.
The three density tiers come from every major worm guide. Beginners stock 0.5 pounds per square foot, about 500 worms per square foot, which gives new colonies room to settle. The standard rule is 1 pound per square foot, about 1,000 red wigglers, and it is the density most suppliers and extension guides quote. Experts may push to 2 pounds per square foot, but only with excellent moisture and airflow, because dense bins heat up and worms stop breeding when crowded. Stay below 2 pounds per square foot when starting out, whatever the bin size.
A 24 by 24 inch bin at 1 pound per square foot holds 4 pounds of worms (about 4,000 worms) and processes about 2 pounds of scraps per day. A VermiHut tray at 11.25 by 11.25 inches has about 0.9 square feet, so one tray at the beginner density needs about 0.2 pounds of worms, and all 5 trays need about 1 pound. A 10 gallon tote offers about 1.5 square feet and suits 1 to 1.5 pounds, an 18 gallon tote about 2.5 square feet and 2 to 2.5 pounds, and a 30 gallon tote about 3.5 square feet and 3 to 3.5 pounds.
Red wigglers (Eisenia fetida) are the standard worm farm and vermicomposting worm: surface dwellers that breed fast and tolerate bin life, unlike garden earthworms or nightcrawlers. Feed fruit and vegetable scraps, coffee grounds, tea bags, bread and grains, and crushed eggshells; avoid meat, dairy, oils, citrus and onions, which cause odour and pests. Keep the bin at 55 to 77 F, moist but not soaking, with ventilation holes near the top and drainage below, and bedding of shredded newspaper or cardboard replaced every few months. Check the bin about once a week for moisture, food and worm health.
The classic errors are sizing by volume instead of surface area, overstocking a new bin, and overfeeding. A tall narrow bin looks big but gives worms little usable surface, since they stay near the top. Overstocking heats the bin and drives worms to escape, while overfeeding rots scraps before worms reach them and brings fruit flies and smells. Start at the beginner density, feed about half a pound of food per pound of worms while the bin establishes, and let the population grow into the space.
Multiply bin surface area in square feet by your stocking density: 0.5 pounds per square foot for beginners, 1 pound for a standard bin, up to 2 pounds for experts. A 24 by 24 inch bin (4 square feet) needs 4 pounds at the standard density, about 4,000 red wigglers.
About 1,000 worms, a mix of mature worms, juveniles and egg cocoons. One pound also measures about two full measuring cups. Suppliers sell by weight, not by count, so the count is always approximate.
About half their body weight per day once established, or 1.75 to 2.45 pounds per week per pound of worms. New bins eat more slowly, so start at about half a pound of food per pound of worms until the colony settles.
Allow about 2 square feet of bin surface per person contributing scraps. A 2 foot by 2 foot bin suits two people, and a 14 to 18 gallon tote suits about 1,000 worms. Depth should be 12 to 24 inches; deeper bins add little usable space.
Red wigglers prefer 55 to 77 F. Below that they slow down, and above about 85 F they start dying. Keep the bin indoors, in a basement or shaded garage, and never in direct sun.
Avoid meat, fish, bones, dairy, oils, citrus and onions: they smell, attract pests, and harm the worms. Stick to fruit and vegetable scraps, coffee grounds, tea bags, bread, grains and crushed eggshells.
Usually overfeeding or too much moisture. Stop adding food, let the bin dry slightly, add dry bedding, and make sure air holes are open. Once the smell fades, resume feeding in smaller amounts.
Yes, if it has a lid, ventilation holes near the top, and drainage holes below with a tray to catch liquid. Plastic totes, wooden crates and purpose-built tray systems all work, as long as the surface area suits the worm count.