Neutral plane
![An evenly loaded beam, bending (sagging) under load. The neutral plane is shown by the dotted line.](/Images/godic/202501/29/Bending.svg4930.png")
![Platinum-iridium standard metre bars of Tresca section. The neutral plane of the bar is designed to coincide with one surface of the central web connecting the two sides (in this photo the bottom surface) and the meter is defined by two fine lines scribed near the ends of the bar on this surface.](/Images/godic/202501/29/Platinum-Iridium_meter_bar4930.jpg")
In mechanics, the neutral plane or neutral surface is a conceptual plane within a beam or cantilever. When loaded by a bending force, the beam bends so that the inner surface is in compression and the outer surface is in tension. The neutral plane is the surface within the beam between these zones, where the material of the beam is not under stress, either compression or tension.