Marx dedicated his life to showing that surplus value extraction can be relatively quantified. Emprically, prices and Marx's Value show strong correlation:
“…the results of the studies we cited above, in combination with the results on the structure of prices in the Greek economy, provide substantial evidence for the empirical strength of the labour theory of value. The latter appears to be a very useful analytical tool for the study of the behavior of a typical capitalist economy.”
Example pulled from this handy doc going over common criticisms of Marxist economics.