Why Bin Size Matters

Vermicomposting—using worms to turn kitchen scraps into nutrient-rich compost—is an eco-friendly way to reduce waste. The key to success is giving your worms enough space to work. An undersized bin can lead to odors, excess moisture, and unhappy worms, while an oversized bin takes up unnecessary room. The Worm Bin Size Calculator helps you estimate the ideal surface area for your bin based on how much food waste you generate each week and how many worms you plan to start with.

Red wigglers, the most common composting worms, eat roughly half their weight in scraps each day. A pound of worms—about 1,000 individuals—can process 3 to 4 pounds of food per week. By matching your household's scraps with an appropriate worm population and bin size, you'll create a balanced system that efficiently turns leftovers into black gold for your garden.

How the Calculation Works

The calculator divides your weekly food scraps by the processing rate of the worms. We assume one pound of worms can handle around 3.5 pounds of scraps per week. Each pound of worms needs roughly one square foot of surface area in the bin. Multiply your worm count by one pound per thousand worms to get the total pounds. Then multiply that by one square foot to get the surface area. Finally, we recommend a bin depth of 12 to 18 inches so the worms have enough bedding.

For example, if you expect two pounds of food scraps per week and you have 1,000 worms (about one pound), you'll need a bin with around one square foot of surface area. A plastic tote measuring 12 by 12 inches with air holes drilled in the sides works perfectly. If you produce more scraps, simply scale up the bin size or add more worms.

Choosing Bedding Materials

Worms need moist, airy bedding to thrive. Shredded newspaper, cardboard, coconut coir, and finished compost all work well. Moisten the bedding until it feels like a wrung-out sponge—damp but not dripping. Fill your bin about three-quarters full with bedding before adding worms. As they consume food and bedding, periodically mix in fresh material to maintain volume and prevent compaction.

Avoid feeding worms large amounts of citrus, spicy foods, or oily scraps. These can upset the bin's balance or attract pests. Bury scraps under the bedding to discourage fruit flies, and monitor moisture levels. If the bin becomes too wet, add more dry bedding; if it dries out, mist with water.

Harvesting Finished Compost

After several months, you'll notice dark, crumbly castings collecting in the bin. To harvest, move contents to one side and add fresh bedding and food to the empty side. Over a few days, most worms will migrate to the new area, allowing you to scoop out finished compost from the vacated side. This nutrient-rich material can be mixed into potting soil, sprinkled around garden plants, or brewed into compost tea.

Example Calculation

Let's say your household generates 5 pounds of scraps each week, and you plan to start with 2,000 worms. Divide 5 by 3.5 to see that roughly 1.4 pounds of worms are needed to process that amount comfortably. Since you already have 2,000 worms—about 2 pounds—you're covered. Multiply the worm pounds by one square foot to get about 2 square feet of surface area. A bin that's 18 inches by 16 inches with a depth of 12 inches would provide ample room for the colony.

Conclusion

Setting up a worm bin is a straightforward way to recycle kitchen scraps and produce excellent compost. Using our calculator ensures you build a bin that matches your waste output and worm population. With the right size and proper care, your worms will happily transform leftovers into a valuable soil amendment year-round.