30:1

The stable ratio depends on how degradable the C source is, but the microbial biomass contains about 12 C/ N

Dear Dr Himanshu Tiwari . The ideal value is around 30:1, (or 30 parts carbon for each part nitrogen) by weight. See the link: http://compost.css.cornell.edu/chemistry.html#:~:text=The%20ideal%20C%2FN%20ratio,each%20part%20nitrogen%20by%20weight.

Kindly see also the following useful link: https://www.nature.com/articles/srep35266

Also check please the following very useful link: http://www.fao.org/3/i3388e/i3388e.pdf

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwjYocm-gaf2AhXjT2wGHffQACIQFnoECD4QAQ&url=https%3A%2F%2Fsoilhealthnexus.org%2Fresources%2Fsoil-properties%2Fsoil-chemical-properties%2Fcarbon-to-nitrogen-ratio-cn%2F&usg=AOvVaw3ZgtG2YZy8kud_hLfGzNtE ( 10 : 1 ) .

The carbon to nitrogen (C/N) ratio is significant in composting because microorganisms need a good balance of carbon and nitrogen (ranging from 25 to 35) in order to remain active. High C/N ratios can lead to prolonged composting duration and low C/N ratios enhance nitrogen loss. To provide optimal amounts of these two crucial elements, you can use the carbon-to-nitrogen (C/N) ratio for each of your compost ingredients. The ideal C/N ratio for composting is generally considered to be around 30:1 or 30 parts carbon for each part nitrogen by weight.

The ideal C:N ratio for the good compost is 6 to 25. C:N ratio indicates the ratio between the Total Carbon/Total Nitrogen content of the products.

Youcan check the following very useful link: http://www.fao.org/3/i3388e/i3388e.pdf

The ideal C:N in composting is 30:1. This recommended ratio allows for optimum composting without, or with minimal N loss. Remember, N content of whatever compost being produced is HIGHLY VALUABLE.

Carbon and nitrogen are the most important of the many elements required for microbial decomposition of organic matter to produce compost.

Generally, we accept the best ratio as being either 25:1 to 30:1.   That is 25 or 30 parts carbon to each part nitrogen by weight.  Other sources recommend a range of between 20:1- 40:1.  At the lower C: N ratios there will be excess nitrogen provided which can result in the production of ammonia. This has the unpleasant odor that many composters will experience at some time in their composting career.  At C: N ratios of over 30:1 there will not be enough nitrogen to support sufficient microbial growth and the microbe population will be too low to produce sufficient heat with the result that the decomposition process will be very slow.

@Dear, Dr. Himanshu Tiwari for more relevant information please go through this link: http://www.carryoncomposting.com/416920203 https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/carbon-to-nitrogen-ratio

Kindly read the question properly. The question is what is the best C:N ratio of the final compost, not during or before composting.

In soil humus C:N ratio may vary from 8 to 12 with an average of 10. Dead microbial bodies also have similar C:N ratio. We expect very good or well decomposed or humified manure or compost to have C:N ratio near 12. But practically it difficult to obtain compost with C:N ratio less than 15. Normally good composts generated by different methods may have C:N ratio nearer to 20:1. Manures and composts with C:N ratio around 25 will decompose well in soil. Living/ active microbes may also have C:N ratio 24-25. Legume straws and some not so well decomposed composts with C:N ratio in the range of 25 to 30 also may decompose well on application to soil. During the process of decomposition the microbial activity will be accelerated and on the death of microbes the nutrients will be released. Only with C:N ratio of 35 or greater there may be limitation of N and immobilization of N by microbes during decomposition of organic matter. From the very well decomposed or humified manures there may be nitrate leaching. But they will have high nutrient and water holding capacity.

The ideal C/N ratio for composting is generally considered to be around 30:1, or 30 parts carbon for each part nitrogen by weight.