Coffee tables range in height, as there's no standard height across the board. Most stand from about 16 to 18 inches high, though 20 inches high is not uncommon. Some coffee tables have tops that raise and lower to accommodate different uses, allowing you to raise the top to eat or use a laptop computer, then lower it to watch television.
The height of your sofa seat cushion should influence the height of your coffee table. If you find your sofa seat cushion sits at 20 inches above the floor, but your coffee table is 16 inches high, the coffee table will feel dwarfed and uncomfortable to use. Try to find a coffee table that is within 1 or 2 inches of the height of your seat cushion.
Another important consideration, if you use your living room for watching television, is the height of your television and stand. Very modern stands are typically low to the ground. When a coffee table is used with such a stand, placing a tall glass on the coffee table can block your view of the television, making TV watching uncomfortable. In this case, find a lower coffee table.
The final important consideration for the appropriate coffee table height is whether you'll be doing much entertaining in your living room with your coffee table, or whether you'll use the space for dining often. If you will use it often for dining or entertaining, a taller table will be more comfortable to eat from when seated on your sofa.