Complex variables and factors are taken into consideration. Those factors are summarized in two coefficient: K1 (Isohumic coefficient) and K2 (coeff. of mineralization), and for those you have to go back to literature and find the values for the soil you are testing, and apply then the fomula of Hénin-Dupuis (Hénin S., Dupuis M., Essai de bilan de la matière organique du sol, Ann. Agron.11 (1945)17-29.).

Please see attached link (old paper but consistent finding)

This is in the case you want to add the compost to the soil as an organic amendment. But if it's just for the humus quality, it's quit a wide name but there is a way to analyze the different composition of the humus (humic acids, fulvic acids, humine...) just see the IHSS portal for further analysis protocols.

Khalid AZIM

http://link.springer.com/article/10.1007%2FBF02205588#page-1

http://www.humicsubstances.org/index.html

   Mr.Barlow ,in the literature I have come across conversion percentage of 30-50 from added organic material to compost in different methods.I can not exactly tell for green waste which may contain some woody material also.But the real problem is to quantitatively assess the proportion of really humified material in compost .A greater proportion can be converted to humus if all the composting conditions and processes are properly controlled.Sufficient time for curing or attaining of maturity of compost is needed as this may not be possible in 'quick composting' methods.

Dear Philip,

Many factors involved in Humus. As Mr Azim said two of most important factors are Isohumic coefficient and coefficient of mineralization.

But all this this depends on Green waste. Green waste can contain different concentration of N, P, K, Ca and other elements and this concentration influence too different on transformation of organic matter.

I think that the quality and type of green waste are most important factor.  

Thank you for your helpful replies