Library · Substrate & soil
Worm Castings Calculator.
Worm Castings Calculator
Size your vermicompost system. From kitchen scraps to commercial production. Bin volume, worm population, feeding rate, harvest math.
The vermicompost framework
| Rule of thumb | Number |
|---|---|
| Worms eat their body weight per day (red wiggler, optimal) | 1 lb worms eat ~0.5-1.0 lb scraps/day |
| Surface area required | 1 sq ft bin per 1 lb worms (or per 1 lb daily feed) |
| Bedding-to-food ratio | ~3:1 by volume (carbon-rich bedding dominates) |
| Moisture target | 70-80% (squeeze test: drips a few drops) |
| Optimal temperature | 60-77°F (red wigglers slow below 50, die above 90) |
| Optimal pH | 6.0-7.5 |
| Worm population doubling | ~3 months under good conditions |
| Castings yield | ~50% of input feed weight (after moisture loss) |
Species comparison
| Species | Best temp | Eat rate | Notes |
|---|---|---|---|
| Red wiggler | 60-77°F | 0.5-1× body weight | The standard. Cold-tolerant, prolific, high-density. Best for indoor/basement. |
| European nightcrawler | 55-75°F | 0.5-0.8× body | Larger; great fishing bait + castings. Slightly slower reproducer. |
| African nightcrawler | 70-85°F | 0.7-1.2× body | Tropical; needs warm temps. Largest worm; fastest cycle. Dies below 55°F. |
| Indian blue | 70-85°F | 0.6-1× body | Tropical; very fast reproducer. Tends to crawl out under stress. |
Best feed and what to avoid
| Excellent | OK in moderation | Avoid |
|---|---|---|
| Fruit + vegetable scraps; coffee grounds + filters; tea bags; eggshells (crushed); bread (small amounts); pasta; aged manure (cow, horse, rabbit) | Citrus (small amounts; acid); allium (onion, garlic; small amounts); cooked food; pumpkin seeds | Meat / fish / dairy; oily/fatty foods; pet manure (parasites); pet/human food with salt; anything spoiled or moldy in quantity |
Castings vs vermicompost vs worm tea
- Pure castings: Just the worm-processed material. Highest microbial diversity and plant-available nutrients. Use as a topdress or in potting mix at 5-20%.
- Vermicompost: Castings + partially-digested bedding. Less concentrated but high volume.
- Worm tea (aerated brew): Castings extracted in aerated water for 24 hours. Liquid biological inoculant; foliar or root drench. Use within hours of brewing.
- Castings leachate: Liquid that drips out of a worm bin. Not the same as worm tea — leachate can contain anaerobic bacteria; dilute heavily and use with care.
Free under CC BY 4.0. Cite as "OAT Worm Castings Calculator (openagriculturetechnology.com)".