Check the ceiling for the presence of a texture. All popcorn ceilings have a distinctive texture, so if your ceiling is smooth, similar to the adjacent walls, it is not a popcorn ceiling.
Feel the ceiling texture. A popcorn ceiling is a rough texture with a very course grain. The ceiling will appear sandy or gritty in texture, but usually covered in a white paint.
Look for patterns in the ceiling. Many ceilings have a repeating pattern that is created using various tools such as brooms, brushes and rags pulled across drywall compound. This is not popcorn ceiling, as popcorn ceilings have a random texture. If your ceiling has texture that is random in nature and consists of small, round bits of material, it is a popcorn ceiling.