2.

Diameter
Circumference
Calculation
1
3.14
2
6.28
2x3.14=6.28
3
9.42
3x3.14=9.42
4
12.56
4x3.14=12.56
5
15.70
5x3.14=15.70
10
31.40
10x3.14=31.40
100
314.00
100x3.14=314.00
123
386.22
123x3.14=386.22
146.5
460.01
146.5x3.14=460.01

The number 3.14 is given a special name in mathematics: pi, and it is represented by the symbol π.