Fe78Si9B13 thin films having a controlled weak perpendicular anisotropy resulting in dense stripe domain configuration have been prepared to investigate their rotatable anisotropy properties. Vector vibrating sample magnetometry, an innovative field-dependent magnetic force microscopy, and ferromagnetic resonance techniques have been jointly exploited to correlate the perpendicular anisotropy to the threshold field value that must be overcome to induce the stripes realignment. A linear relationship between these two quantities is found. The presence of the threshold field is attributed to the portions of the samples whose magnetisation must flip its perpendicular component during a rotation process, therefore encountering the energy barrier of the perpendicular anisotropy.