Your degree classification is based on marks gained in course modules at Levels 2 and 3, and under the classification method a grade awarded at Level 3 (in your third year) has twice the weight of a grade awarded at Level 2. The calculation is a two-stage process which takes into account the average grade (mean average) and the range of grades (median average) achieved at each Level.
The video here explains how we calculate your final degree classification https://www.sheffield.ac.uk/ssid/course/degree-classification/index