Compost Calculator

How to use this calculator;

  1. Choose a material from the drop down list. (if your material doesn't appear then choose a similar material from the list)
  2. Enter the amount of material you have by volume (this could be in cubic feet, cubic metres, buckets full, wheelbarrow loads, etc)
  3. Press TAB
  4. Whammo! The Total C:N ratio for your mix will appear below the form.
Keep modifying the volume of each ingredient until you find the mix that gives you a carbon to nitrogren ratio of around 25:1. A mix lower than 20:1 will be too "hot" and a mix greater than 40:1 may take a very long time to compost.

 

For great compost aim for a total C:N ratio of around 25:1

 

Material Volume

 
The calculator takes care of all the complex maths to do with moisture content, available carbon vs locked away carbon and converting carbon:nitrogen by mass into carbon:nitrogen by volume.

 

Now all you need to do is follow the step's in Kirsten's wonderful rapid compost making videos, and you will be soon be drowning in piles of lovely humus rich composty goodness.

 

As much as we would like to claim credit for this marvelous piece of mathematics it is actually a simplified version of a great compost mix calculator developed by John Longfellow and hosted by the Klickitat County Office in Washington State in the US of A.

 

For a whole bunch of technical info about the data which drives this calculator please visit the Klickitat County's page.
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Comments (10)add comment

Kathleen Mc said:

Hi milkwooders,
Brilliant! I will be passing this on.
Kathleen
October 12, 2007 | url

Spontaneous stephanie (Aldinga said:

Ohhhh I love your calculator. Now i know what I have been doing wrong. Too much nitrogen! Way too much. I have been dabbling over the last 12 months, but the poor results have left me rather dishartened. Will give it another go with this new tool - thanks
November 14, 2007

Mel said:

I love this - thank you again! We were not sure of the proper recipe for our compost. But this tool brings everything into focus. We will be using rabbit manure in our compost, which I believe is similar to horse manure.

Here's what we came up with:

40 lbs. Vegetable Waste
100 lbs. Horse Manure
10 lbs. Poultry Manure
300 lbs. Straw Wheat
makes a mix with a total available C:N Ratio of 25:1
February 05, 2008 | url

Derek Leeder said:

Some confusion on my part, on this page you say a Carbon / nitrogen ratio to aim for with ingredients is 25:1. I am reading that as 25 carbon to 1 nitrogen.
The Klickitat County calculator says 25 C to 30 N....roughly a 40/60 mix.
Which one ?
A top website and I wish you both well.
Derek
May 13, 2008

Nicko said:

Hi Derek,

I had another look through the Klickitat County page to try and find the reference to using a 25 C to 30 N mix and could not find it.

I have alway been taught that compost will not work unless your carbon nitrogen ratio is between 20:1 and 40:1. A lower ration that 20:1 will make a very rich rotten egg gas producing anaerobic pile of gloop and a higher ratio than 40:1 will just be a pile of loose ingredients.

What you are suggesting is a C:N ratio of 2:3 or 1:1.5 this would be a pile of Urea or other very high nitrogen material.

Make sure you don't confuse the total carbon nitrogen ration with the ration of high carbon material and high nitrogen materials. Even high nitrogen materials like chicken manure have more carbon in them than nitrogen.

Make sure you watch Kirsten's compost videos... she'll set you straight.

May 13, 2008 | url

Derek Leeder said:

Thanks Nick, what I did was click on the link back up this page ",,,,great compost mix calculator developed by John Longfellow...." and misunderstood what was above the calculator box.
I see what you're saying now.
Regards
Derek
May 14, 2008

Kali said:

Thanks for not only offering such great information and useful tools, but also such playful tutorials and good remedies for the serious. You inspire me to have as much creative fun in working the land!

I have a question for you. I heard that if you don't have enough nitrogen content in the compost, you can add some of your own urine, which is rich in nitrogen. What do you think about this? Also, I'm soaking thistles and nettles in water for a few weeks and adding the strained, nutrient rich tea to the compost. Don't know how to factor urine or weed teas into C:N ratio. Any ideas or experiences with this?

Thanks. And keep inspiring us!
Kali (aspiring towards permaculture in a woodland in France)
April 04, 2009

Nicko said:

Urine has a very low Carbon:Nitrogen ratio... almost 1:1 it is an excellent addition to compost, but can be a little difficult to handle.

It's easiest to use it fresh... (ie pee directly onto the pile), but it's hard to gather enough via this method to make a difference. You DO NOT want to store it in liquid form, urine is practically sterile when it leaves the body, but it is so rich in nitrogen (proteins) that anaerobic bacteria quickly colonises it and produces that horrible stale urine smell.

One good way to deal with this is to fill a bucket with very high carbon material, sawdust, wood-chips or shredded paper and then pee in that. Once you have filled the bucket you will have something around 5:1, still very rich. Use it quick smilies/smiley.gif
April 05, 2009 | url

Doug Fox said:

This calculator has one big shortcoming: it does not calculate the total percent moisture (which should be targeted at about 50%). I have my students build their recipes based on moisture content first (balancing their primary material such as food waste with some available bulking agent such as straw), then they calculate C:N to see if it is okay. One other flaw: waste hay, our favorite carbon material, is not listed, and straw is so much ligher that it can't be used as a substitute in the formula. Doug
June 15, 2009 | url

Tracy said:

Great calculator - I used it to build my first hot compost pile yesterday and it'was hot when I checked this afternoon! Much better than my previous efforts with a compost bin at the back door with too many food scraps and not enough carbon smilies/smiley.gif
December 14, 2009

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