You've picked your color, but how many gallons will you need for your room? Calculate the wall area of the room; you'll need one gallon for 450 square feet. To determine the wall area, multiply the height of each wall by its width (don't subtract for doors and windows unless they take up more than half the wall); total the figures for the walls. Add 10 percent for future touch-ups. For two coats, double the number.
Easily remove a popcorn ceiling with this new ceiling scraper @Megan Bledsoe if you ever decide it is worth it. I've also seen some cool pins to cover popcorn ceilings with other surfaces. I have a cool all white embossed pattern wallpaper ceiling in my kitchen