A printing fluid container (100) for use in a printing system is described. An example container includes a base (110) and a light transmissive side wall (120). The side wall extends from the base to define a chamber (130) for receiving and storing printing fluid within the container. The side wall has an internal surface (122) facing the chamber, said internal surface comprising a channel (140). The channel comprises a portion (142) indicating a height from the base, the height representing a predetermined fill amount. The channel is configured such that when the chamber contains printing fluid, printing fluid resides within the channel (140) and indicates the predetermined fill amount.