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Cost Per Click (CPC) is the amount an advertiser pays each time a user clicks on a paid ad, determined by auction dynamics, quality score, and bid strategy. CPC is the fundamental pricing unit for search, social, and display advertising. Managing CPC effectively is critical to controlling overall customer acquisition costs in paid channels.

Cost Per Mille (CPM) measures the cost an advertiser pays per 1,000 ad impressions, making it the standard pricing metric for brand awareness and display advertising campaigns. CPM is the base pricing model for most programmatic display, video, and social media advertising. It shifts optimization focus from clicks to reach and frequency.

Click-Through Rate (CTR) measures the percentage of people who click on a link or ad after seeing it, expressed as clicks divided by impressions. It is used across paid advertising, email marketing, organic search, and display campaigns to measure how compelling content is at driving engagement. CTR is a leading engagement signal but must be interpreted alongside conversion rate to assess true campaign value.

Return on Ad Spend (ROAS) measures the gross revenue generated for every dollar spent on advertising. It is calculated at the campaign, channel, or account level and indicates how efficiently paid media is converting spend into revenue. ROAS is commonly used to optimize paid channel budgets and set performance targets for media teams.