Cost per like (CPL) is a metric that's used by marketers who want to evaluate the effectiveness of a social media campaign on Facebook. The goal of CPL is to quantify how many advertising dollars must be spent to get a Facebook member to “Like” a particular Facebook page.
In 2013, Facebook started offering a cost-per-action (CPA) bidding option on ads. Facebook provides their advertisers with a way to assess CPL, but the social media company has faced criticism because their method for determining cost per like isn't always clear.
The challenge for companies is to determine the value of Facebook fans based on factors such as how likely a fan is to spend money, how wide and engaged the fan's social network is and how likely a fan is to spread the word about a brand, product or service.
Before investing in a CPL approach to Facebook advertising, companies will need to decide if Facebook members who "like" a page on Facebook can be depended upon to take desireable actions. While tracking cost per like or cost per action can be an important part of a company's advertising strategy, cost per acquisition (CPA) still remains the most important metric. Companies must also need to consider the impact of owned and earned media on Facebook engagement, rather than just focusing on paid advertising. Owned media includes the brand's Facebook page, and possibly websites, blogs, and other social channels leading to Facebook, while earned media includes content generated by people outside of the company as a result of the company's PR or media efforts. Determining the return on investment of these media efforts is another important component of a successful Facebook strategy.
CPL can be contrasted with the more traditional Internet advertising metrics, including cost per thousand impressions (CPM), which is based on how many people view the ads, and cost per click (CPC), which is based on how many people click on an advertisement.