A post base is gadget used to help hold a post in place. It can be used to hold a post used for building structures, such as pole barns.

A typical post base looks like a large bracket that forms two 90° angles, while one end remains opened. The post that is being installed is inserted in this open area so it rests flat against the bottom of the post base. The other side of the post base generally has two protrusions. These protrusions are intended to be inserted in cement located at the bottom of the hole into which the post is to be inserted.

In order to use a post base, one must attach it to the bottom of the post with screws. A hole for the post must be dug, and cement is poured into the hole. The post, complete with post base, is placed inside the hole, with the protrusions of the post base inside the wet cement. It should usually be embedded about one inch (2.54 centimeters) from the base plate of the post base. This allows the majority of the wood portion of the post to stay out of the cement while still being held in place by the post base.

Since the post base is in the ground, it is generally made of galvanized steel in order to prevent decay. Although a post base is made of galvanized steel, it is not capable of providing enough resistance to keep the post from rotating if too much pressure is placed on it. For this reason, a post base should not be used for posts that will not be supported at the top, such as fence posts.

Using a post base to install posts rather than embedding them directly into concrete helps the posts last longer in the ground. In fact, a post embedded in concrete with a post base can usually last for around 50 years. This type of post base typically costs less than 20 US dollars (USD).