Described is a method for determining a telegram length in an operating apparatus for communicating between the operating apparatus and a field device via a network. The method comprises composing a first telegram in the operating apparatus. The first telegram comprises a predeterminable first telegram length, and the composed first telegram is despatched via the network to the field device. After the first telegram has been despatched, the operating apparatus waits for the receipt of a second telegram, which second telegram is received by the operating apparatus via the network. After successful receipt of the second telegram, the first telegram length is increased by a predeterminable value. Increasing the value takes place until receiving the second telegram fails. After the receipt of the second telegram has failed, the first telegram length that has resulted in successfully receiving the second telegram is provided.