Kisii receives an average rainfall of 1500 millimeters, with long rains falling in March and June. Maximum temperature range between 21 °C – 30 °C (69.8 °F – 86 °F) and minimum temperatures range between 15 °C – 20 °C (59 °F – 68 °F).
There is total population of 1,266,860 of which 605,784 are males, 661,038 females and 38 intersex persons. There are 308,054 household with an average household size of 4.1 persons per household and a population density 958 people per square kilometre.