Average Temperatures in Stockholm, Sweden. 1  The mean annual temperature in Stockholm, Sweden is a little cool at 6.6 degrees Celsius (43.9 degrees Fahrenheit). 2  There is a variation of average monthly temperatures of 20.2 C (36.4 F) which is a below moderate range. There is a variation of average monthly temperatures of 20.2 C (36.4 F) which is a below moderate range. 2  The variation/ range of diurnal mean temperatures is 6.3 C (11.4 F).