CTR, CPC, CPM, CPA

Every ad metric is one division.

Ad platforms hand you a wall of acronyms. Every one of them is just "this divided by that". Once you see it, you can convert between them in your head.

The move

CTR = clicks ÷ impressions. CPC = spend ÷ clicks. CPM = spend ÷ impressions × 1,000 ("M" is Latin for thousand). CPA = spend ÷ conversions. The connector: CPM = CPC × CTR × 1,000.

Worked example

CPC is $2 and CTR is 1.5%. What’s the CPM?

  1. 1,000 impressions × 1.5% = 15 clicks
  2. 15 clicks × $2 = $30 CPM
  • "Cost per X" always means spend ÷ X.
  • CPA = CPC ÷ conversion rate. $3 clicks converting at 5% → $60 per customer.