Immobility due to movement impairments causes many secondary conditions that are a threat to a person’s health and quality of life. Wearable robotic mobility aids such as exoskeletons and exosuits are a promising technique to tackle immobility. These devices are attached to the human with cuffs. However, the physical interaction at the human-robot interface is not yet well understood. Misplacement and compression of soft tissue diminish the efficiency of the robot and the comfort for the human. We developed a measurement method that allows us to simultaneously measure cuff interaction forces in normal and tangential direction. The measurement setup was validated in a friction test bench. The test-retest reliability was evaluated in an isolated attachment cuff mounted on a human forearm. Force measurements were repeatable, with error ranges up to 28.7% or 7.8 N in normal, 28.7% or 2.3 N in tangential direction. Our method is the first approach that simultaneously measures normal and tangential forces at the physical interface of wearable robots. The test-retest reliability is within the range of methods that assess only normal forces.