The first step in determining the size of the tree is finding the perfect spot for it to go. One important consideration while doing this is whether you want the tree to become the main focus of attention in the room, or if you would prefer a festive yet overall simpler look.
There are a variety of reasons you may want a tree that you can place up on a table or mantel, perhaps you wish to keep it out of the way of small children or pets. If this is the case, a mini tree may be perfect for you. These trees are less than 4 ft, giving the room an appropriate holiday feel without dominating it.
If, on the other hand, you are looking for a more definite Xmas vibe, but are working with a smaller space, then a small tree (4-5.5 ft) could work well for you. Place it in a less-trafficked area of the room, such as in a snug corner, to prevent it from getting bumped.
For many, a medium tree (6-7.5 ft) is the most popular option. This is the standard size and looks great in most living rooms. It creates a beautifully festival focal point, especially if placed in an area of prominence such as in front of the window.
Large trees (8-10.5 ft) can make a bigger room look absolutely magical, particularly if you have space to pull it right out into the center of the room. Make sure that you carefully measure the height of the room first to ensure that it can comfortably accommodate the tree. Go for one at least six inches lower than your ceiling to prevent the tree from bending at the top and to allow space for adding a tree topper.
There is also an extra-large tree option (12 ft+) to be used in truly cavernous rooms or ones with high ceilings. If you have the space and want to turn the entire place into a winter wonderland - then go for it. Just ensure when measuring, you are taking into account the base of the tree.