Carbon to Nitrogen Compost Calculator: Create the Perfect Compost Pile

Do you want to create a perfect compost pile? Well, according to the USDA, the ideal carbon to nitrogen rate for optimal microbial action in a compost pile is between 20:1 and 40:1, with 24:1 being the absolute sweet spot.

So, you can either build a pile and hope for the best… or, you can use our compost calculator to help make sure your compost pile has good carbon to nitrogen ratios.

We've compiled the following list of carbon to nitrogen ration for compost materials from every reliable resource we could find. Now, those ratios are based on averages and actual C:N may vary a bit, however, these will still give you a really good idea of how much carbon to nitrogen you are putting in your pile.

How to Use the Compost Calculator

Using the calculator is very easy. You need to fill in how many “parts” of each compost ingredient you are planning to add to your pile. Then, scroll to the bottom to see if your ingredients add up to the ideal carbon to nitrogen ratio of between 20 to 40 to 1.

If they do, you can go and make your compost pile! If they don't, then add more parts of browns or greens, as needed, to get your compost pile recipe just right.

What is a “Part”?

A part can be any unit of measure that is useful to you. The key is to use the same measure of a part for every ingredient you put in your pile. For example, on the homestead 5-gallon buckets, wheelbarrows, or recycled feed sacks full of stuff are often used as a part.

Let's say you have a few 5-gallon buckets of kitchen scraps as your nitrogen heavy ingredient (often called greens). If you plan to use straw which is carbon heavy (often called brown) to get the right C:N, then you'll want to eye-ball and decide how much straw you need to make a similar sized ‘part' as a 5-gallon bucket.

This does require some imagination because kitchen scraps are heavy and moist. So, they squish down quite a bit. Straw, of course, is light and airy and doesn't compress so much. Likely, you'll want to err on the side of imagining an over-stuffed bucket of straw to make it similar to a more compressed bucket of kitchen scraps.

Since these ratios are averages and you can be between 20-40 on the carbon and still get good results, chances are you'll guestimate your parts just fine for good compost.

What About Using Weights?

You can also use weights. However, much of the weight difference in composting ingredients comes from water. Food wastes and many manures have lots of water in them. Dried leaves, straw, and paper have very little water in them.

If you want to work with weights, then you need to get the moisture level in your different compost ingredients to be about equal. That may require wetting browns and straining greens.

Or, you can weigh a small sample of your greens, dry it out, and weigh it again. Divide the ending weight by the original weight (e.g., 10 pounds wet, 1 pound dry is 1 lb. / 10 lb. = 0.10 lb.) Then, weigh your total greens, multiply them by your earlier results (e.g., 100 pounds wet x 0.10 = 10 pounds), and use the calculated figure as your number of parts for the calculator.

Browns that are totally dry, can be weighed as is. That total weight becomes your parts for entry into the calculator.

Things to Remember About Compost Piles

Compost calculatorCompost calculator

The real key to our compost calculator – whether you use weights or other units of measure like buckets and wheelbarrows – is to convert your various compost materials into some unit of measure that lets you compare apples to apples.

Don't worry! After making a few good compost piles, you'll get really good at this skill.

Also, your pile needs to end up at about 60% moisture. While kitchen scraps may already have a C:N of 20:1 and might technically be in the microbial sweet zone, they are also about 85-90% moisture.

So, you'll usually need to mix browns in with your kitchen scraps too. The browns will absorb the extra moisture and keep the air flowing, so your pile doesn't become anaerobic and stinky!

If your materials are quite wet, then push towards the 40:1 side of things. If they are closer to 60% moisture already, then shoot for the magic 24:1.

Carbon to Nitrogen Compost Calculator

Now, without further adieu, I present to you the most comprehensive carbon to nitrogen compost calculator we could create using a list of sources so long, you'll need to scroll down for ages to get to the bottom.

Common Browns

MaterialsC/N RatioPartsCarbon
Cardboard, Shredded3500
Hardwood Bark2230
Hardwood Mulch/Chips5600
Leaves – Dried600
Leaves – Green450
Newspaper, Shredded4500
Pine Needles800
Sawdust3250
Softwood Bark4960
Softwood Mulch/Chips6410
Straw – Oat600
Straw – Wheat1200
Wood Chips Mixed4000

Cover Crops

MaterialsC/N RatioPartsCarbon
Alfalfa120
Annual Rye260
Buckwheat340
Clover230
Cowpeas210
German Foxtail Millet440
Hairy Vetch110
Japanese Millet420
Mustard260
Pearl Millet500
Soybeans200
Sudangrass440
Winter Wheat140

Household Waste

MaterialsC/N RatioPartsCarbon
Ashes, Wood250
Coffee Grounds200
Garden Waste300
Grass Clippings200
Hair or Fur100
Kitchen Scraps200
Leaves – Fresh370
Paper Towels1100
Shrub Trimmings530
Toilet Paper700
Tomato Canning Waste110
Tree Trimmings160
Weeds – Dried200
Weeds – Fresh100

Crop Related Compost Materials

MaterialsC/N RatioPartsCarbon
Apple Pomace130
Banana Leaves250
Coconut Husks and Shells1800
Corn Cobs800
Corn Stalks750
Fruit Waste350
Grape Pomace (Winery Waste)650
Grape Vine Prunings800
Hay – Grass400
Hay – Legume200
Legume Shells (e.g. Pea, Bean)300
Olive Husks300
Peanut Shells350
Rice Hulls1210
Vegetable Waste – Leafy100
Vegetable Waste – Starchy150

Animal Manures

MaterialsC/N RatioPartsCarbon
Alpaca – Manure Only160
Alpaca Litter450
Bat Guano30
Chicken – Manure Only60
Chicken Litter160
Cow – Manure Only150
Duck Litter160
Goat Manure110
Horse – Manure Only300
Horse Litter/Bedding700
Humanure70
Llama – Manure Only200
Pig140
Rabbit Manure120
Sheep150
Turkey Litter160
Urine0.80

Miscellaneous

MaterialsC/N RatioPartsCarbon
Crab and Lobster Waste50
Fish Waste50
Lumber Mill Waste1700
Meat Processing Wastes30
Seaweed100
Spent Grains – Large Brewery120
Spent Grains – Microbrew150
Water Hyacinth250

Compost Activators

MaterialsC/N RatioPartsCarbon
Blood Meal140
Cotton Seed Meal70
Soybean Meal70

Carbon to Nitrogen Ratio

Total Carbon Value0
Total Nitrogen Value0
Carbon to Nitrogen Ratio

Compost Calculator Conclusion

If you happen to know C:N ratios for anything not already on the list, please let us know and well add it into our compost calculator. May your compost microbes be happy and your garden be exceptionally fertile as a result!

List of References

  • http://extensionpublications.unl.edu/assets/html/g1315/build/g1315.htm
  • https://www.planetnatural.com/composting-101/making/c-n-ratio/
  • https://ucanr.edu/sites/mginyomono/files/170818.pdf
  • http://cwmi.css.cornell.edu/AppendixATable1OFCH.pdf
  • http://agrienvarchive.ca/bioenergy/download/barker_ncsu_manure_02.pdf
  • http://www.carryoncomposting.com/416920203
  • http://docs.nmcomposters.org/2014-mc-project-bw.pdf
  • http://humanurehandbook.com/downloads/H4/Ch_09_Compost_Nuts%20and%20Bolts.pdf
  • http://sweeta.illinois.edu/composting-horsebedding.cfm
  • http://vermontllamaalpacaassociation.blogspot.com/2012/05/composting-your-camelid-manure-101.html
  • http://docs.nmcomposters.org/carbon-nitrogen-ratio-simplified.pdf
  • https://compost-turner.net/composting-technologies/grape-stalks-and-pomace-composting-process.html
  • https://bit.ly/2Knvgsh [URL too long]
  • https://www.agweb.com/article/understand-carbon-to-nitrogen-ratios-before-buying-cover-crop-seed/
  • https://www.webpal.org/SAFE/aaarecovery/1_farm_recovery/humanure/newchapter03_07.htm
  • https://content.ces.ncsu.edu/summer-cover-crops
  • https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.1928.tb06729.x
  • cespubs.uaf.edu/index.php/download_file/1258/
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