Digital Advertising

How to Calculate ROAS, CPA, and CPC (With Break-Even Math)

By Yana Markova · November 12, 2026 · 8 min read

Three metrics show up in nearly every paid media report: ROAS, CPA, and CPC. They are simple to calculate, and just as simple to misread. This guide gives you the formulas, worked examples (clearly hypothetical), and the break-even math that tells you whether a number is actually good.

The three formulas

CPC (cost per click)

CPC = total ad cost ÷ number of clicks

CPA (cost per acquisition, also called cost per conversion)

CPA = total ad cost ÷ number of conversions

ROAS (return on ad spend)

ROAS = revenue from ads ÷ ad cost

ROAS can be written as a ratio (4:1), a multiple (4x), or a percentage (400%). They all mean the same thing: every dollar of spend returned four dollars in revenue.

Worked examples (hypothetical numbers)

Say a campaign spends $2,000, gets 800 clicks, produces 40 conversions, and those conversions bring in $10,000 in revenue. These numbers are made up to show the math.

  • CPC = $2,000 ÷ 800 = $2.50
  • CPA = $2,000 ÷ 40 = $50
  • ROAS = $10,000 ÷ $2,000 = 5.0 (500%)

You can also move between them. Conversion rate = conversions ÷ clicks = 40 ÷ 800 = 5%. Then CPA = CPC ÷ conversion rate = $2.50 ÷ 0.05 = $50. This shows why improving conversion rate lowers CPA even if CPC stays the same.

Why “good” ROAS depends on your margin

There is no universal “good” ROAS. A 4x ROAS can be profitable for one business and a loss for another. The number that matters is your break-even ROAS:

Break-even ROAS = 1 ÷ profit margin

If your margin on a sale, before ad costs, is 40% (0.40), break-even ROAS = 1 ÷ 0.40 = 2.5. Below 2.5 you lose money on each sale. Above it, you earn a profit on the ad spend. At a 25% margin, break-even is 4.0.

You can do the same for CPA:

Break-even CPA = average profit per conversion (before ad costs)

If you make $80 in profit per sale before ad costs, you can afford a CPA up to $80 and still break even. Anything lower is profit.

Use your real margins to set targets. Do not copy a benchmark from a blog post, including this one.

Where these numbers mislead you

  1. Platform-reported conversions are not all equal. A form fill, a phone call, and a purchase are not worth the same, yet a single CPA can lump them together.
  2. Revenue is not profit. ROAS ignores product cost, shipping, refunds, and overhead.
  3. Attribution changes the answer. Different attribution models assign credit differently, so ROAS in Google Ads may not match GA4 or your CRM.
  4. Lead gen needs lead quality. For service businesses, a low CPA can come from junk leads. What matters is cost per qualified lead or per booked job.
  5. Averages hide segments. Campaign-level ROAS can hide a profitable product line and a loser that cancel each other out.
  6. Lagging revenue. If sales close weeks later, the report will understate ROAS until the data catches up.

Lead gen: measure what happens after the form or call

For lead-generation businesses, two practices make these formulas trustworthy:

  • Track the source of every call and form. Call tracking with dynamic number insertion (CallRail is one common option) ties each call to the campaign and keyword that drove it.
  • Upload qualified leads back to Google Ads as offline conversions, with a value where job sizes vary. This lets Smart Bidding optimize toward real customers instead of raw lead volume, and it makes your CPA and ROAS figures reflect business results. Google restricts how long after a click you can upload a conversion, so check the current window in its documentation and upload the qualified lead stage promptly.

A simple calculator you can build in a spreadsheet

If you would rather not build one, use our free ROAS calculator, CPA calculator, and CPC calculator. To build your own, make these input cells: spend, clicks, conversions, revenue, profit margin. Then add formula cells:

  • CPC = spend ÷ clicks
  • Conversion rate = conversions ÷ clicks
  • CPA = spend ÷ conversions
  • ROAS = revenue ÷ spend
  • Break-even ROAS = 1 ÷ margin
  • Profit after ads = revenue × margin − spend

Add a status cell that says “above break-even” or “below break-even” by comparing ROAS to break-even ROAS. That one comparison is more useful than all the benchmark tables on the internet.

From calculation to action

A second example: a lead-gen business

Here is a hypothetical service business to show why CPA alone can mislead. It spends $3,000, gets 60 leads, and ends up with 12 booked jobs worth $500 in profit each before ad costs. These numbers are invented for illustration.

  • CPA per lead = $3,000 ÷ 60 = $50
  • Cost per booked job = $3,000 ÷ 12 = $250
  • Profit before ads = 12 × $500 = $6,000
  • Profit after ads = $6,000 − $3,000 = $3,000

If you only watched the $50 CPA, you could not tell whether the campaign was profitable. The cost per booked job and the profit after ads give the real answer. This is why qualified-lead tracking matters.

Free tools and related reading

Free tools on this site:

Related guides:

Want these numbers tracked down to qualified leads and booked jobs, not just clicks? Our digital advertising and retention and tracking services set up call tracking and offline conversion uploads. Get in touch.

Frequently asked questions

What is a good ROAS?

It depends on your margin. Compute break-even ROAS as 1 ÷ margin and aim above it. A higher target makes sense if you want to grow profit and not just break even.

What is the difference between ROAS and ROI?

ROAS compares revenue to ad spend. ROI compares profit to total investment, so it accounts for costs beyond advertising.

Is a lower CPA always better?

Not always. A very low CPA can mean low-quality conversions. Compare CPA to the value of each conversion.

How do I calculate ROAS as a percentage?

Multiply the ratio by 100. A ROAS of 4.0 is 400%.