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Urban Worm Calculator Guide

Use this handy guide to understand how the Urban Worm Calculator can help you predict worm reproduction, how much you can harvest without decreasing your worm population, how many pounds of worm castings you can produce, and more!



Settings Area

Unit of Measurement: Makes your units reflect metric or standard.

Currency: Lets you choose one of 7 currencies.

Basic Input Area


Basic Input Area

Summary: These are the simplest inputs. Once these are filled, a sidebar “Scoreboard” appears (pictured below) and your Result Section becomes partially populated.
Start Date: This is simply the date you assume your worms start multiplying.
Starting Quantity: This isn't really a quantity, but weight.
Monthly Reproduction Rate: This ranges from 0-200 percent but defaults to 25%, which equates to the oft-cited ” double every 90 days” statistic. While it is a monthly rate, it compounds daily so assuming no die offs or harvesting, you will get slightly better actual reproduction that the number you enter.   Clicking the orange button will give you the option of entering reproduction rates specific to each month. Note: If you neglect to enter a rate for a certain month, it assumes zero reproduction for that month.

"The Scoreboard"

“The Scoreboard”

Advanced Input Area


Advanced Settings Area

Quantity Goal: This allows you to set a goal for how many lbs or kg you want to reach. Assuming you entered a Start Date and Starting Quantity, entering a number here calculates the date you will reach that goal, which you will see in the “scoreboard” that will appear to the right of the screen.
Maximum Surface Area: Enter your best guess of how much surface area you have for vermiculture or vermicomposting..
Population Density: How much worm weight per surface area do you think you'll have? Once you enter that number here, the Scoreboard will automatically show you the month and year you will reach your maximum capacity for vermiculture or vermicomposting.
Worm Unit Retail Value: This is where it gets kind of fun! How much do you think you will be able to sell your worms for per lb or kg? Once you enter a number here, the Scoreboard will show a projected value of what your worms will be worth at the end of the 12th and 24th month from your Start Date.
Castings Retail Value: Same as above except there is no number to look at on the scoreboard. You'll find a number for Daily Castings Retail Value in the Results Section, which I will describe later.
Monthly Die Off: This allows you to identify a percentage of your worms that you assume will die each month. This also allows a monthly specific percentage.
Monthly Harvest: This field allows you to indicate how much worm weight you'll be harvesting each month. Don't forget to use the monthly-specific option for a more precise prediction.
Goal Sustainable Harvest: This handy feature allows you to enter a desired amount of worms you would like to harvest monthly without reducing your stock from one month to the next. Once you enter a number, the scoreboard shows what month and year you will reach that goal.
Date to Start Harvest: This date defaults to the current date but allows you to specify when you will start harvesting your worms.  Note: There is a small glitch here where the Scoreboard will go blank if you enter a Date to Start Harvest without actually entering a Monthly Harvest. But entering a number as small as .00000001 will allow you to get around this.
Vermicomposting Efficiency: I give a little love to the vermicomposters here. This number represents the percent of your worms' weight they will eat each day. It assumes you have composting earthworms and defaults to 50% but up to 100% is selectable.
Vermicast Output %: This is the percentage of worm food you assume will be converted to castings. To be honest, this number could be a wild guess, but I set the default to a nice, round 10%.  This number will tend to be low because 70-90% of most food scraps are water weight.

Sidebar “Scoreboard”


The Scoreboard automatically pops up whenever you have enough information entered for it to make its first calculation.

"The Scoreboard"

“The Scoreboard”

Because your Start Date and Monthly Reproduction Rate are pre-populated with default values, this will appear whenever you enter your Starting Quantity.

Date to Reach Quantity Goal:  Given that you've entered a Quantity Goal, this will tell you what month and year you'll reach it.
Date to Reach Sustainable Harvest Goal: As you can imagine, this tells you when you'll reach your Sustainable Harvest Goal, if you entered one.
Date to Reach Max Capacity: If you entered a Max Surface Area Available and Population Density values, this will calculate when you'll run out of space for vermiculture or vermicomposting.
Worm Retail Value in 12 Months:  If you enter a Worm Unit Retail Value (price per pound/kg), it will tell you the financial worth of your inventory at the end of the 12th month after your Start Date.  Note:  The first month's results are only the results between the Start Date and the end of the month.  This is important because if you run this calculator today and run it again tomorrow using the exact same figures, you will get slightly different numbers as you will be working with one less day.
Worm Retail Value in 24 Months:  Surprise!  This gives you the financial value of your inventory at the end of the 24th month after your Start Date. And this is the most eye-popping display of compounding interest a worm farmer is likely to see.

Results Section

This section gives you a 24-month breakdown of your results. Most columns are self-explanatory, but I will explain a little bit of how we came up with the numbers.


Results Area

Month: The first row reflects end of the current month, not one month or 30 days from the start date.

Qty (Quantity): This reflects the quantity of the previous month plus reproduction minus and harvests and die offs.

Daily Vermicomposting Capacity: Given an entered Vermicomposting Efficiency, this reflects the amount of weight in food or food waste your worms could process each day. Warning: think of this as a weight to work towards as opposed to a weight you can just dump in your bin/bed/flow-through, especially if you have set 100% for Vermicomposting Efficiency. I don't want the Urban Worm Calculator – or me – held responsible for a stinky, overheated bin!

Daily Castings Output:  Given an entered Castings Unit Retail Value, this is the financial value of the worm castings produced that day.

Castings Retail Value: This reflects the value of the castings your worms will produce daily by the end of the month. A future version may include a cumulative value of the castings produced for the entire month.

Worm Retail Value:  This is the total value of your worm inventory on that date.

Sustainable Harvest: This is the worm weight you could harvest each month without reducing your worm stock below the level of the previous month. If you think of this as a financial calculator – and that's pretty much what it is – this is the interest minus any withdrawals in for the form of die offs and harvests from previous months.

Sustainable Harvest Value:  This is the financial value of your Sustainable Harvest.

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