Using quantum distance, magnetic susceptibility in the non-interacting limit can be rigorously split into two contributions: one arising solely from band dispersion, while the other stems from quantum geometric contributions. In this paper, we apply this decomposition to two materials, LaFeAsO and Pb9Cu(PO4)6O, and demonstrate that their dominant magnetic fluctuations originate from the geometric contribution. In LaFeAsO, stripe-type antiferromagnetic fluctuations arise primarily from quantum geometry, while in Pb9Cu(PO4)6O the geometric term suppresses antiferromagnetic fluctuations and stabilizes ferromagnetic fluctuations. Our findings highlight the essential role of quantum geometry in governing magnetic fluctuations in multiband systems, and provide a unique and quantitative framework to disentangle band-structure and wave-function-geometry effects that have often been discussed collectively as multi-orbital effects.