Estimate wine bottles per guest.
The figure worth committing to memory is five glasses per bottle: a 750 ml bottle holds 25.4 fluid ounces and a standard pour is five, so a bottle serves five glasses — not the six or seven people often assume, and fewer still if pours are generous. From there the calculation is glasses per guest across the event, converted to ounces and divided by the bottle. Consumption is front-loaded, so one and a half glasses in the first hour and one an hour after is a better model than a flat rate. Rounding to whole cases is worth doing because most retailers discount by the case, and unopened bottles keep.
Wine Per Guest
Glasses per guest = first hour + (hours - 1) x later hours; ounces = guests x glasses x pour size; bottles = ounces / bottle size, rounded up; glasses per bottle = bottle size / pour
Quantity planning only. Serve alcohol responsibly, provide food and non-alcoholic alternatives, never serve anyone under the legal drinking age, and make sure guests have a safe way home.
Five at a standard five-ounce pour. A generous six-ounce pour gives four, which is why bottles disappear faster than expected at a party.
Roughly 60% white and sparkling to 40% red in warm weather and the reverse in cold, adjusted for what you are serving. Buy by the case where possible, since unopened bottles keep and case discounts are significant.