An on-board device (5) for measuring the weight of an aircraft (G), the device comprising a hollow element (3) extending from a first end (11) to a second end (12) and a bar (4) extending inside said hollow element (3) from an embedded end (13) to a free end (14). The free end (14) has first and second sensors (21, 22) respectively for taking first and second distance measurements, said device (5) further including processor means (50) connected to the first sensor (21) and to the second sensor (22) to generate an alert when a sum of the first measurement plus the second measurement varies, and secondly a processor unit (60) connected to at least one of said sensors (21, 22) for determining information relating to weight.