180 DEGREE RULE

This schematic shows the axis between two characters and the 180° arc on which cameras may be positioned (green). When cutting from the green arc to the red arc, the characters switch places on the screen.

In filmmaking, the 180° rule is a basic guideline that states that two characters (or other elements) in the same scene should always have the same left/right relationship to each other. If the camera passes over the imaginary axis connecting the two subjects, it is calledcrossing the line. The new shot, from the opposite side, is known as a reverse angle.

In the example of a dialogue between two actors, if Owen (orange shirt in the diagram) is on the left and Bob (blue shirt) is on the right, then Owen should be facing right at all times, even when Bob is off the edge of the frame, and Bob should always be facing left. Shifting to the other side of the characters on a cut, so that Bob is now on the left side and Owen is on the right, will disorient the viewer, and break the flow of the scene.

In the example of an action scene, such as a car chase, if a vehicle leaves the right side of the frame in one shot, it should enter from the left side of the frame in the next shot. Leaving from the right and entering from the right will create a similar sense of disorientation as in the dialogue example.

An example of sustained use of the 180 degree rule occurs throughout much of The Big Parade, a 1925 drama about World War I directed by King Vidor. In the sequences leading up to the battle scenes, the American forces (arriving from the west) are always shown marching from left to right across the screen, while the German troops (arriving from the east) are always shown marching from right to left. After the battle scenes, when the weary troops are staggering homeward, the Americans are always shown crossing the screen from right to left (moving west) and the Germans from left to right (moving east). The audience's viewpoint is therefore always from a consistent position, in this case southward of the action.