The ferromagnetic susceptibility of a magnetoelastic amorphous metal ribbon is determined from the coupled equations of motion for the magnetization and strain modes. This analysis is used to calculate the dynamic sensitivity and field equivalent noise floor of a metallic glass low‐frequency magnetometer. Two principal noise sources are considered: the thermally induced magnetization fluctuations and the Johnson noise of the pick‐up coil. The magnetometer exhibits a calculated minimum detectable field of ∼0.1 pT/(Hz)1/2for room temperature operation at a resonance frequency of 22 kHz and 103turn pick‐up coil having a 200‐&OHgr; resistance. The fundamental material limit is estimated to be ∼5 fT/(Hz)1/2.