Driven by the need of a simple method to arrive at rather accurate molecular mass key data for different lignin samples across different laboratories, we revisited thoroughly the different aspects that comprise the determination of molecular weight key data of lignins by means of gel permeation chromatography. We considered setup issues and their effect on calibration, implications emerging from sample preparation, issues connected to data acquisition, and effects of raw data evaluation. Considering identified key issues, we propose a standardized setup in connection with a standardized data treatment that ensures the generation of precise GPC results. The introduction of an additional lignin-type depending correction factor, which is delineated using averaged bidimensional NMR-based advanced structural information obtained for a given lignin type, allows us to account for system-inherent bias, rendering the precise measurements de facto accurate.