Vermicomposting Worm Population & Weekly Scrap Feeding Calculator
Buying too few worms leads to rotting, smelly scraps piling up faster than they can be processed, while an oversized bin wastes space and bedding. This calculator sizes your starting worm colony and bin surface area to match your household's actual weekly food scrap volume.
Your bin can handle 7.0 lbs/week of scraps with about 2.00 lbs of worms.
| Metric | Value |
|---|---|
| Weekly kitchen scraps | 7.0 lbs |
| Worm pounds needed | 2.00 |
| Estimated worm count | 2,000 |
| Minimum surface area | 2.00 sq ft |
| Actual bin surface area | 2.67 sq ft |
| Bin capacity (lbs scraps/week) | 9.3 |
- 1.
WormLbsNeeded = WeeklyScraps_lbs / 3.5 - 2.
MinSurfaceArea_sqft = WormLbsNeeded × 1.0 - 3.
BinSurfaceArea_sqft = (Length_in × Width_in) / 144
How to Use This Calculator
1. Enter your details
Use the labelled fields and units that match your situation.
2. Calculate instantly
The result, visual comparison, and working update as values change.
3. Review your result
Check assumptions, then copy, print, or share the calculation.
Formula & step-by-step maths
- 3.5
- Weekly scraps processed per lb of worms
- 1.0
- Sq ft surface area needed per lb of worms
The 50% body weight rule
Healthy red wigglers eat roughly half their body weight in scraps per day, which works out to about 3.5 lbs of scraps processed weekly per pound of worms — the core ratio this calculator is built on.
Why surface area matters more than depth
Worms feed near the surface where oxygen is available, so a wide, shallow bin processes more waste than a deep, narrow one of the same volume. The 1 lb of worms per square foot rule reflects that surface-feeding behavior.
Red Wigglers vs European Nightcrawlers
Red Wigglers are the vermicomposting standard — voracious eaters that tolerate bin conditions well. European Nightcrawlers eat slightly less per pound but grow larger and double as fishing bait, so many keepers choose them for dual purposes.
What not to feed your worm bin
Avoid citrus, onions, garlic, and meat/dairy in large quantities — acidic and pungent scraps can drive worms away from feeding zones or attract pests, while meat and dairy rot before worms can process them.
Worm bin sizing reference
| Weekly scraps | Worms needed | Min bin surface area |
|---|---|---|
| 3.5 lbs | 1.0 lb | 1.0 sq ft |
| 7 lbs | 2.0 lbs | 2.0 sq ft |
| 10.5 lbs | 3.0 lbs | 3.0 sq ft |
| 14 lbs | 4.0 lbs | 4.0 sq ft |
| 17.5 lbs | 5.0 lbs | 5.0 sq ft |
| 21 lbs | 6.0 lbs | 6.0 sq ft |
Frequently Asked Questions
Three worked examples
Same engine, three different starting points — useful if you want to see how sensitive the answer is before you type your own numbers in.
Example 1: weekly kitchen scraps 5.46 lbs/week, worm species "Red Wigglers (Eisenia fetida)"
On the lower / more conservative end. Your bin can handle 5.5 lbs/week of scraps with about 1.56 lbs of worms.
Example 2: weekly kitchen scraps 7 lbs/week, worm species "Red Wigglers (Eisenia fetida)"
A typical middle-of-the-road setup. Your bin can handle 7.0 lbs/week of scraps with about 2.00 lbs of worms.
Example 3: weekly kitchen scraps 9.1 lbs/week, worm species "European Nightcrawlers"
On the higher / more demanding end. Your bin can handle 9.1 lbs/week of scraps with about 2.60 lbs of worms.
Quick answers about the Worm Composting Sizer
What exactly does the Worm Composting Sizer work out?
Buying too few worms leads to rotting, smelly scraps piling up faster than they can be processed, while an oversized bin wastes space and bedding. You enter weekly kitchen scraps, bin length, bin width and worm species and the result panel updates straight away, so you can compare two or three versions of the same question in a few seconds.
What do I need before I start?
Only 4 fields: weekly kitchen scraps, bin length, bin width and worm species. Nothing else is needed and nothing is stored.
How is it calculated — the 50% body weight rule?
Healthy red wigglers eat roughly half their body weight in scraps per day, which works out to about 3. The same maths runs inside this page, so hand-checking the result on paper gives you the identical figure.
Why do two calculators give me different answers for worm Composting Sizer?
Worms feed near the surface where oxygen is available, so a wide, shallow bin processes more waste than a deep, narrow one of the same volume. Different sites pick different assumptions, so always check which method a calculator states before you trust the gap between two numbers.
What does the "Worm bin sizing reference" table on this page tell me?
It is the reference range this tool works against — 6 rows from "3.5 lbs" (1.0 lb) up to "21 lbs" (6.0 lbs). Use it to sanity-check whether the number you just calculated sits where you expected it to.
Which worm species should I pick?
The dropdown offers 2 choices — Red Wigglers (Eisenia fetida) and European Nightcrawlers. Pick the one that matches your real situation rather than the one you would like to be true; worm species usually moves the final figure more than any other single input, so it is worth running it twice with the option above and below your guess.
Do I have to press a button or reload the page to see the result?
No. Worm Composting Sizer runs completely inside your browser, so the moment you change a value the cards recalculate — there is no submit step, no page reload and no waiting for a server round trip. That also means it keeps working on a weak or intermittent mobile connection.
Is it free, and do you keep what I type?
It is free with no sign-up, no app install and no usage limit. Nothing you enter into Worm Composting Sizer leaves your device — the calculation is JavaScript running locally, so there is no upload of your figures to DrHint or anyone else.
Can I use it on a phone?
Yes — the layout stacks to a single column on small screens and the number fields open the numeric keypad on both Android and iOS. Many people bookmark this page or add it to their home screen and re-open it whenever the question comes up.
Anything to be careful about with the result?
About 1. Treat the output as a well-grounded estimate for planning, not as a professional, legal or medical decision on its own.
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