This can be measured along several diferent dimensions. HDI and related indices provide different ways of looking at this. There are also more subjective means of measuring this (e.g., happiness index). Sometimes the subjective means of measuring qiality of life is useful, as quality of life can be interpreted differently by differentpeople.
Quality of human life may be measured by measuring the level of satisfaction one derives from physical, mental & intellectual plane and integrating the same for a period of time. There could be some difficulties, as needs and wants are different for different persons belonging to different social stratum.
In my research, I have split out Potential Quality of Life (time available after needs are met) from Actualized Quality of Life (time available after needs are met, as if all needs are met). Finding and improving that Potential is very much an engineering exercise, while Actualizing that potential is a Human Development process that I don't know enough about and would be pleased to discuss it with you.