Both intracellular and extracellular metabolite measurements are needed to calculate absolute metabolic fluxes. Different tools can be used to measure compounds in different parts of metabolism. Tools shown in green measure concentrations, which can be converted to fluxes using time-course measurements and stable isotope tracers, while tools in red can directly measure rates. These tools can then be integrated to determine the fluxes across multiple metabolic pathways. LC-MS, liquid chromatography-mass spectrometry; GC-MS, gas chromatography-mass spectrometry; NMR, nuclear magnetic resonance; HPLC, high performance-liquid chromatography; GC, gas chromatography; YSI BA, Yellow Springs Instruments biochemical analyzer; SRS, stimulated Raman scattering; FRET, fluorescence resonance energy transfer; and XFA, Seahorse extracellular flux analyzer.