Soil & Compost

Worm Composting Calculator

Enter how much food waste your household produces each day and this calculator tells you how many red wigglers to buy, what size worm bin you need, and how much bedding to start with.

Average household produces 0.5–1 lb of kitchen scraps daily

Pick a size to estimate scraps, or type your own above

Getting started with vermicomposting

Vermicomposting turns everyday kitchen scraps into one of the richest soil amendments you can give a garden, using nothing but a bin and a colony of worms. The hardest part for beginners is simply knowing how many worms to buy and how big a bin to set up. Enter the pounds of food scraps your household generates each day — or pick your household size to estimate it — and this calculator returns the amount of worms to purchase, a matching bin size, and how much bedding to start with.

Why red wigglers, not garden earthworms

Successful worm bins rely on red wigglers (Eisenia fetida), not the earthworms you dig up in the yard. Red wigglers are surface feeders adapted to the warm, crowded, decaying conditions inside a bin, and they reproduce quickly when food is plentiful. Garden earthworms and nightcrawlers are deep-burrowing soil dwellers; dropped into a bin they become stressed, stop eating, and die. Always start a bin with worms sold specifically for composting.

Feeding rate and bin size

The math behind the tool is simple. Red wigglers (Eisenia fetida) process about half their body weight in food scraps per day — a pound of worms handles roughly half a pound of kitchen waste daily. To keep up with your scraps you therefore want about two pounds of worms for every pound of daily waste, and you give them roughly half a cubic foot of bedding per pound of worms. Smaller households do well with a simple one- or two-cubic-foot tub, while larger volumes call for a flow-through or multi-tray bin that lets you harvest finished castings from the bottom without disturbing the colony.

Setting up and maintaining the bin

Fill the bin with moist bedding — shredded cardboard, newspaper, or coconut coir — until it feels like a wrung-out sponge, then add your worms and bury food scraps beneath the surface. Feed gradually at first so the colony can catch up, chop scraps small to speed breakdown, and add a handful of dry bedding whenever the bin looks wet. Keep the bin between roughly 55 and 77°F, out of freezing cold and direct sun. Within three to six months you will be harvesting dark, crumbly castings to mix into potting soil, side-dress beds, or brew into compost tea.

Frequently Asked Questions

A good rule of thumb is about 2 pounds of worms for every pound of food scraps you add per day, because red wigglers eat roughly half their body weight daily. For a typical household producing half a pound to a pound of scraps, that means starting with 1 to 2 pounds of worms (around 1,000 to 2,000 wigglers). If your budget is tight, start with 1 pound — the population roughly doubles every two to three months until it matches the available food.
Use red wigglers (Eisenia fetida), sometimes sold as red worms or tiger worms. They are surface feeders that thrive in the warm, crowded, food-rich conditions of a bin. Common garden earthworms and nightcrawlers are burrowing soil dwellers — they will not survive or reproduce in a worm bin, so do not dig worms from the yard and expect them to work.
Feed them fruit and vegetable scraps, coffee grounds and paper filters, crushed eggshells, tea leaves, and small amounts of bread or grains. Avoid meat, fish, dairy, oily or greasy food, and large amounts of citrus, onion, or garlic, which can turn the bin acidic and smelly. Chop scraps small and bury them under the bedding to speed things up and deter fruit flies.
Most bins are ready for a first harvest in about 3 to 6 months, once the bedding and food have been transformed into dark, crumbly, earthy-smelling castings. Flow-through and multi-tray bins let you harvest finished castings from the bottom while the worms keep working up top, so you can collect smaller amounts more often.
A healthy bin smells earthy, like a forest floor — not foul. Bad odors almost always mean too much food or too much moisture, which creates anaerobic (oxygen-starved) conditions. Fix it by feeding less, mixing in dry bedding such as shredded cardboard, and making sure the bin drains and breathes. A balanced bin is essentially odorless.
Red wigglers are happiest between about 55 and 77°F (13–25°C), so keep the bin out of freezing cold and direct summer sun. A basement, garage, kitchen, or shaded porch all work well. In very hot or cold climates, move the bin indoors during temperature extremes to keep the colony comfortable and productive.

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GardenCalc Editorial Team

Horticulture Writers & Master Gardeners

Our calculators and guides are written and fact-checked by gardeners with hands-on experience in vegetable production, soil management, and home landscaping.