To determine the size of wedding cake for your guest count, you can use tiers as a guideline. For example, a 16-inch round cake can typically feed 100 guests. If you have 75 guests, a 3-tiered cake with 6-, 8-, and 10-inch tiers would be suitable. For 125 guests, a 4-tiered cake with 6-, 8-, 10-, and 12-inch tiers would be needed. If you have 200 guests, you can choose a 4-tiered cake with 8-, 10-, 12-, and 14-inch tiers or a 3-tiered cake with 12-, 14-, and 16-inch tiers.