With a full champagne flute, you can get about 5.5 glasses per bottle, but you can double that by serving half flutes. You can estimate 1-2 glasses at the welcoming reception in the first hour, 1 glass per toast and then 1-2 more every hour.
How to calculate how much wine you will need:
|#of guests||#of glasses/ guest||total glasses||5.5 glasses/bottle||#of bottles needed|
|25||25 x 2.5||62.5||63/5.5 = 11.45||12|
|50||50 x 2.5||125||125/5.5= 22.72||24|
|75||75 x 2.5||188||188/5.5= 34.18||36|
|100||100 x 2.5||250||250/5.5= 45.45||48|
Always allow a little extra in case of breakage or unexpected toasts. If you do have a bottle or two left over you can always save it to celebrate your first anniversary together or another celebratory occasion.