Phosphorus intergranular segregation is known to influence the fracture properties of steels by decreasing grain boundary cohesion and induce intergranular fracture. Different techniques such as Angle-Resolved X-ray Photoelectron Spectroscopy (AR-XPS), Wavelength Dispersive Spectroscopy (WDS), Energy Dispersive X-ray Spectroscopy coupled with Scanning Transmission Electron Microscope (STEM-EDX), and Atom Probe Tomography (APT) can be used to quantify intergranular segregation. Although many studies of this phenomenon were conducted over the last decades, there are rarely direct comparisons between different techniques and there is still a need of reliable and comparable quantification methods for grain boundary segregation. This study cross-compares four available techniques (AR-XPS, WDS, STEM-EDX, and APT) to quantify phosphorus interfacial segregation within the same grain of a sample. This was done by fabricating a Fe-P-Fe sandwich specimen with phosphorus segregated at the interface. Attention was paid to the way of expressing the results of the different techniques so that they can be compared with one another. The quantification results from the different techniques show reasonable agreement.