I don't remember the exact amount, but I've developed 4x5 in 5x7 trays that were just under half full. I've done as many as 8 sheets at a time with no problem other than it taking forever because I do one at a time to avoid scratches. I recently got a tank that can hold 12 sheets. I plan on using that because the extra chemicals are worth it to save the time, to have less to clean up, and to have better control of the temperature.