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Get the Best Compost Mix With This CN Ratio Calculator

Use A CN Ratio Calculator To Mix Compost Correctly.

Many gardeners have made compost for years, and they know what materials to mix to get good results. What if you’re gaining experience or have a lot of materials to add to your compost pile? In that case, it helps to know how to calculate the CN ratio. Fear not, because we made that easy with this CN ratio calculator.

Why Should I Use a Calculator for Composting?

A calculator is the easy way to get the right mix of materials. If the materials are way out of balance, you’ll have a dead compost pile, or a stinky glob. Yuck!

The correct Carbon to Nitrogen ratio for a compost pile is 25 – 30:1. That means 25 – 30 parts of Carbon to 1 part of Nitrogen (hence the C:N ratio). This calculator allows you to select up to four Browns (for Carbon) and 4 Greens (for Nitrogen).

A higher C:N ratio (over 30:1) means the Carbon (Browns) is too high, so you have to add more Nitrogen (Greens). Likewise, a lower C:N ratio (under 25:1) means the Nitrogen (Greens) is too high, so you have to add more Carbon (Browns).

Making compost isn’t quantum physics. If the ratio is close, you’ll be successful. The problems happen if you mix in too much of one type of material. This calculator makes it easy to work out the correct mixture.

Too much total Carbon (Browns), like dry leaves or straw, makes a dry, dead pile. The microorganisms and fungi won’t be active.

Too much total Nitrogen (Greens), like kitchen scraps or livestock manure, causes high moisture content. That makes a wet, smelly pile since the wrong microorganisms are active. They end up making ammonia from the Nitrogen.

When either of these things happen, there’s a solution. Adjust the compost pile by adding more of the Browns or Greens that are low or missing.

You can avoid these problems by using this Carbon Nitrogen Ratio Calculator.

A garden made with compost after using a CN ratio calculator.
Making compost the right way is one more step to a productive garden.

What About the “Parts” Sections on the C:N Ratio Calculator?

The word “parts” is a catch-all term for any measuring device. It could be a bowl, bucket, wheelbarrow, or dump truck. What matters is that you measure everything with the same object at the time you’re mixing. Here’s a real example:

  • Suppose you’re throwing a bucket of straw (a Brown) onto the pile. You need to use the same bucket to measure any other Browns or Greens. The bucket is the “part” you’re using to measure with.
  • The next day, your neighbor gives you a wheelbarrow full of mixed wood chips (a Brown). You need to use that wheelbarrow to measure the correct amount of Greens to mix with the wood chips. This time, the wheelbarrow is the “part” you’re measuring with.
  • You’re sure to have the right C:N ratio when you use consistent measurements (parts).

If you have to mix a quarter, half, or three-fourths of a part, enter the decimal value: .25, .5, .75, or whatever amount you need.

We can revise this CN ratio calculator if needed. We can add more selections or act on other suggestions you might have. Email us at to let us know what you need.

Click on these links for more information about composting or even compost tumblers. We recommend the composting article for everyone. It has important information for more successful composting.

Do you want to know about the math behind this calculator? Download our pdf about how to calculate the C N ratio manually.

We hope this compost calculator is a great help for you and makes you a Victorious Gardener.

Bob Styer

As a child, I hated gardening. That was mainly because Dad expected us to work in the garden every so often even though we thought play was more important. Over the years, though, I've developed a real appreciation for growing things. Whether you're growing plants for food or to enjoy their beauty, gardening can make your life better. Seize the moment!

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