ROAS vs ROI vs CPA vs CPC
ROAS, ROI, CPA, and CPC are the core paid media metrics — but they measure different things. Using the wrong one leads to scaling campaigns that look good in dashboards but lose money in your P&L.
Quick answer
ROAS measures revenue per ad dollar; ROI measures profit per ad dollar. CPA is cost per conversion; CPC is cost per click. Use break-even ROAS for tROAS bidding and max CPA for Target CPA.
- ROAS — revenue per ad dollar. Best for ecommerce efficiency, but ignores margin.
- ROI — profit per ad dollar. Best for business-level profitability reporting.
- CPA — cost per conversion. Best for lead gen and conversion-focused campaigns.
- CPC — cost per click. Best for bid caps and keyword affordability at your conversion rate.
Tie every metric to a break-even threshold from your margin — use the Break Even ROAS Calculator, Max CPA Calculator, and Max CPC Calculator.
Definitions and formulas
| Metric | Formula | What it tells you |
|---|---|---|
| ROAS | Revenue ÷ ad spend | How much revenue each ad dollar generates |
| ROI | Profit ÷ ad spend | Return on investment as profit relative to spend |
| CPA | Ad spend ÷ conversions | Cost to acquire one conversion (sale, lead, or signup) |
| CPC | Ad spend ÷ clicks | Cost per click — depends on conversion rate for profitability |
ROAS (Return on Ad Spend)
ROAS is revenue-focused. A 3× ROAS means $3 in revenue for every $1 spent. It is the default metric in Google Ads and Meta Ads because platforms track revenue easily.
When to use it: Ecommerce campaign optimization, comparing ad sets, and setting minimum performance floors — but only against your break-even ROAS from margin, not a generic target.
Limitation: ROAS ignores product costs. A 4× ROAS campaign with 20% margins loses money; a 2.5× ROAS campaign with 60% margins can be highly profitable.
ROI (Return on Investment)
ROI measures profit relative to spend. If you spend $1,000 and earn $250 in net profit (after product costs and ad spend), ROI is 25% on that spend.
When to use it: Business-level decisions, comparing paid ads to other channels, and reporting to stakeholders who think in profit terms.
Limitation: ROI requires accurate cost data. Many teams lack real-time COGS, so they use ROAS as a proxy and convert using margin assumptions — then confirm with the Ad Profit Calculator.
CPA (Cost Per Acquisition)
CPA is spend divided by conversions. If you spend $500 and get 10 sales, CPA is $50. It directly answers: “What does each customer cost me?”
When to use it: Lead gen, app installs, subscription trials, and any campaign optimized for conversions rather than revenue. Compare CPA against your max affordable CPA (contribution margin per sale). In lead gen mode, the calculator shows max cost per lead; divide by close rate for a CRM closed-deal cap.
Limitation: CPA alone ignores sale value. A $20 CPA is excellent for a $200 AOV product and terrible for a $15 AOV product. For lead gen, compare cost per lead to the calculator cap — then check closed-deal cost in your CRM (cap ÷ close rate).
CPC (Cost Per Click)
CPC is what you pay each time someone clicks your ad. Affordable CPC depends on how much profit you keep per conversion and how often clicks convert: max CPC = max CPA × conversion rate.
When to use it: Manual bid caps in Google Ads, evaluating expensive keywords, and search campaigns where click cost varies widely.
Limitation: A cheap click that never converts is worthless. Use the Max CPC Calculator with your margin and conversion rate.
CPA vs ROAS (and CPA ROAS)
Searchers looking for CPA ROAS or ROAS vs CPA are usually choosing a bid strategy unit — not a different business model. Both describe the same margin math:
- Max CPA = contribution per conversion (dollars you can spend per sale or lead and still break even).
- Break-even ROAS = AOV ÷ contribution (the revenue multiple you need so spend equals contribution).
Break-even ROAS = AOV ÷ max CPA
Max CPA = AOV ÷ break-even ROAS
Example: $100 AOV, $40 contribution → max CPA = $40, break-even ROAS = 2.5×. A campaign at $35 CPA (~2.86× ROAS) is profitable; at $45 CPA (~2.22× ROAS) it loses money.
Use max CPA when bidding on Target CPA / cost per purchase. Use the Break Even ROAS Calculator when bidding on Target ROAS. For Target CPA vs Target ROAS in practice, see the Target ROAS Calculator. Do not mix a ROAS floor with a CPA bid without converting units first.
ROAS vs CPC (and CPC ROAS)
CPC ROAS / ROAS vs CPC queries ask how click cost maps to return on ad spend. CPC alone cannot tell you if ads are profitable — you need conversion rate and AOV (or expected value per lead):
Spend = clicks × CPC
Revenue = clicks × conversion rate × AOV
ROAS = AOV × conversion rate ÷ CPC
Example: $2.00 CPC, 2% conversion, $100 AOV → ROAS = 100 × 0.02 ÷ 2 = 1.0× (one dollar of revenue per ad dollar). If break-even ROAS is 2.5×, that CPC is far too high — or conversion rate / AOV must improve.
Practical path: calculate max CPA from margin, then max CPC = max CPA × conversion rate. Compare live CPC to that ceiling and live ROAS to your break-even ROAS floor.
Example: same campaign, four views
Ad spend = $2,000, sales = 40, AOV = $100, margin = 50%, clicks = 800 (5% conversion)
- Revenue = 40 × $100 = $4,000
- Contribution = 40 × $50 = $2,000
- Profit = $2,000 − $2,000 = $0 (break-even)
- ROAS = $4,000 ÷ $2,000 = 2.0×
- ROI = $0 ÷ $2,000 = 0%
- CPA = $2,000 ÷ 40 = $50
- CPC = $2,000 ÷ 800 = $2.50 — equal to max CPC at 5% conversion ($50 × 5%)
Which metric should you use?
- Ecommerce scaling: Break-even ROAS as your floor, then track profit with ROI or the Ad Profit Calculator.
- Lead gen: Expected revenue per lead = deal value × close rate. Max cost per lead from margin; max closed-deal cost = cap ÷ close rate.
- Bid management: Max CPC from max CPA and conversion rate.
- Executive reporting: Net profit or ROI — not platform ROAS alone.
People also ask
What is the difference between CPA and ROAS?
CPA is cost per conversion in dollars. ROAS is revenue divided by ad spend. Same campaign economics, different units — use max CPA for Target CPA bidding and break-even ROAS for Target ROAS.
How do CPC and ROAS relate?
CPC is cost per click. ROAS is revenue per ad dollar. Convert between them with conversion rate and AOV: spend = clicks × CPC, revenue = conversions × AOV, ROAS = revenue ÷ spend.
Should I optimize for CPA ROAS or CPC ROAS?
Optimize to the metric your bid strategy uses. Target CPA needs a max CPA ceiling; Target ROAS needs a break-even ROAS floor. Max CPC is for manual or CPC-capped bids.
Target CPA vs Target ROAS — which should I use?
Use Target CPA when you bid on cost per conversion in dollars (stable AOV or leads). Use Target ROAS when conversion value varies and you optimize to a revenue multiple. Same contribution math: max CPA = contribution; break-even ROAS = AOV ÷ contribution.