The elevator can ere is a simplified diagram of a typical elevator. With its cabin, guide rails, cable, sheaves, warm gear unit, motor, and something that we call counterweight. The counterweight travels along vertical guide rails opposite to the direction of the elevator car.

The component may appear to do nothing more than just rising and descending, but it in fact plays a very crucial role in the stability and energy efficiency of an elevator. Without it, raising the car will require very high torque once the car is raised. Extremely powerful brakes will be required to maintain the car's position or to lower the car in a controlled manner.

This is why the counterweight is introduced. The basic idea of counterweight is that if there are two equal weights attached to either end of a cable, then the system is perfectly balanced. The only job of the motor is to tip the balance one way or the other. Weight of counterweight is determined by adding the weight of a car and half of the total capacity of elevator.

Let's understand this by using a simple example. Let's suppose the full capacity of elevator is four people. According to the formula counterweight is equal to car plus two people, when elevator is fully loaded there is an imbalance of two people. When elevator is not loaded there is again an imbalance of two people but in opposite direction. This means the imbalance never exceeds two people and the system remains at maximum possible balance under variable loads.