During storage, the invert sugar content of sugar beets increases with increasing storage period and storage temperature, thereby decreasing the processing quality of the beets substantially. Invert sugar results from the enzymatic degradation of sucrose to glucose and fructose. The current methods to determine invert sugar in sugar beets have a low sample frequency and are very expensive and are therefore not implemented in the routine analyses of sugar factories. The content of invert sugar could be calculated based on the glucose content. This requires a constant ratio of glucose to fructose in freshly harvested sugar beets as well as in sugar beets stored under different conditions. The objective of the present study was thus I) to analyse the glucose to fructose ratio of freshly harvested beets and of beets stored under different conditions, and II) to develop a formula to estimate the invert sugar content based on the glucose content of sugar beets. The ratio of glucose to fructose in freshly harvested beets and beets stored under different conditions was quite similar. A close linear relationship between glucose and invert sugar content in freshly harvested and stored beets was found. By using the regression function, the invert sugar content of an independent dataset was calculated based on the glucose content. The estimated invert sugar content was closely correlated with the invert sugar content measured by HPLC. The invert sugar content in freshly harvested and stored sugar beets can thus be calculated with the formula developed in this study. This would considerably improve the quality assessment of sugar beets once the new method to measure the glucose content becomes implemented in the routine analysis in sugar factories.