How to calculate ROAS and cost per buyer
How to calculate ROAS and cost per buyer from ad spend, revenue and buyers, find the break-even ROAS for your margin, and read both with one worked example.
Read the guideCost per buyer and ROAS calculator
Enter what a campaign cost, how many people bought and what they paid. The calculator shows what each buyer cost and whether the ads earn their money back.
How the numbers are calculated
Cost per buyer is ad spend divided by buyers: the people who paid, counted once however many orders they placed. The example is the sample shop’s last 30 days on Google Ads: €312.40 for 41 buyers, €7.62 each.
ROAS is revenue divided by ad spend. €2,870 of revenue on €312.40 of spend is a ROAS of 9.2: every euro of ads came back as €9.20 of revenue. Revenue is not profit, so ROAS alone does not say whether a campaign pays.
Break-even ROAS is one divided by gross margin. At 40 % margin, a campaign needs a ROAS of 2.5 before the ads pay for themselves. The most a buyer may cost is revenue per buyer times margin: €70 × 40 % = €28. Profit after ads is revenue times margin, less spend.
Keep currencies apart: divide euros by euros. And count buyers from your own paid orders, not from the conversions an ad platform reports; the two rarely match.
Cost per buyer for every campaign, every day
Connect Google Ads and MIRA FIVE joins daily spend to the visits it paid for, and shows cost per buyer and ROAS for each campaign from your own paid orders.
Questions and answers
What is a good ROAS?
One above your break-even ROAS, which is one divided by gross margin. At 40 % margin that is 2.5; at 25 % it is 4. A ROAS that looks high can still lose money when the margin is thin.
Why use buyers and not conversions?
An ad platform counts the conversions it touched, can include modelled ones, and two platforms can both claim one order. Buyers come from your own paid orders, each person counted once.
Does the calculator send what I type anywhere?
No. It calculates in your browser; nothing you enter is sent or stored.
Should I include repeat purchases in revenue?
For a campaign’s ROAS, count the revenue from the buyers it brought in the period you look at. Revenue from later repeat orders makes a campaign look better over time; keep the period the same for spend and revenue.