The top chart shows the number of servings that can be expected from a size of a round 2-layer cake.
Size of round cake Servings: 4″ x 2″ x 1”

6

10

8

18

9

23

10

29

12

41

14

56

16

73

18

93

20

114

22

138

24

165

sheet 9 x 13

48

sheet 12 x 16

66

The second chart is a guide based on the number of guests you are expecting. The numbers below exclude the top tier as the bride & groom tend to save it..
Tier Sizes Servings

2-TIER

8-6

16 – 19

10-6

26 – 29

10-8

23 – 30

3-TIER

12-8-6

56 – 64

12-9-6

56 – 99

14-10-6

76 – 89

14-10-8

78 – 90

14-10-8-6

96 – 109

16-12-8

103 – 125

4-TIER

16-12-8-6

121 – 144

16-12-9-6

126 – 144

18-12-10-6

146 – 184

18-14-10-6

161 – 189

20-16-12-8

198 – 230

5-TIER

20-16-12-9-6

231 – 274

20-18-16-12-8

293 – 350

24-20-16-12-9-6

381 – 449