A terminal device for use with a wireless telecommunications network, the terminal device comprising: sensor circuitry configured to detect a value of a parameter which is variable in response to a variation in vertical position of the terminal device; receiver circuitry configured to receive, from infrastructure equipment of the wireless telecommunications network, a reference value of the parameter and a reference value of the vertical position at which the reference value of the parameter is associated; processing circuitry configured to determine a value of the vertical position of the terminal device defined relative to a second reference vertical position, wherein the determining comprises: determining the second reference vertical position based on a geographical position of the terminal device; determining a value of the vertical position of the terminal device defined relative to the first reference vertical position based on the detected value of the parameter; determining the value of the vertical position of the terminal device defined relative to the second reference vertical position based on a difference between the determined value of the vertical position of the terminal device defined relative to the first reference vertical position and the second reference vertical position.