A little arithmetic. A clearer decision.

Average cost per click

CPC calculator

To calculate CPC, divide ad spend by clicks: 600 spent for 300 clicks is a CPC of 2.00. The calculator also works backwards. Enter a CPC and a click target to get the budget you need, or a budget and a CPC to estimate how many clicks it buys. Use one currency and one click definition, and remember a cheap click is not automatically a useful visit.

CPC = spend ÷ clicks

Cost per thousand impressions

CPM calculator

To calculate CPM, divide ad spend by impressions and multiply by 1,000: 150 spent on 30,000 impressions is a CPM of 5.00. The calculator also works backwards. Enter a CPM and an impression target to get the cost, or a budget and a CPM to estimate how many impressions it buys. CPM is the price of 1,000 recorded impressions, not of reaching 1,000 different people.

CPM = spend ÷ impressions × 1,000

Cost per defined action

CPA calculator

To calculate CPA, divide ad spend by the number of conversions: 900 spent for 30 completed enquiries is a CPA of 30.00 per enquiry. The calculator also works backwards. Enter a target CPA and a conversion goal to get the budget you need, or a budget and a CPA to estimate how many conversions it buys. Name the action first, because a lead, a purchase and a new customer give very different CPAs.

CPA = spend ÷ completed actions

Reported return on ad spend

ROAS calculator

To calculate ROAS, divide the revenue (conversion value) from ads by the ad spend: 7,500 of value from 2,500 of spend is a ROAS of 3×, or 300%. The calculator also gives your break-even ROAS (1 ÷ profit margin: 2.5× at a 40% margin), the revenue a target ROAS needs at a given spend, and the most you can spend for an expected revenue at a target ROAS. ROAS measures reported value against media cost only, so it is not profit.

ROAS = conversion value ÷ ad spend

What these calculators cannot tell you

A ratio describes your inputs. It does not establish why a number changed, whether a click was useful or whether a conversion was incremental. Zero denominators are reported as unavailable, never as zero, because a free click or a free outcome is not what the data shows.