Ad Metrics in Plain English: CTR, CPC, CPM, CPA and ROAS

Ad dashboards love acronyms. Before you can decide whether a campaign is working, you need to know what each number is telling you and which ones actually matter for your business.

Here are the core metrics, with formulas and a simple example you can follow along with.

The example campaign

Imagine a small online store runs a campaign with these results (illustrative numbers):

• Spend: ₹20,000
• Impressions: 400,000 (times the ad was shown)
• Clicks: 4,000
• Purchases: 80
• Revenue from those purchases: ₹96,000

CPM: cost per thousand impressions

Formula: spend ÷ impressions × 1,000

₹20,000 ÷ 400,000 × 1,000 = ₹50 CPM

CPM tells you how expensive it is to reach people. It rises with competition (festive season, for example) and with narrow targeting. A high CPM isn't bad by itself if the audience converts well.

CTR: click-through rate

Formula: clicks ÷ impressions × 100

4,000 ÷ 400,000 × 100 = 1% CTR

CTR shows how compelling your ad is to the people who see it. Low CTR usually points to creative, offer or targeting that doesn't match. Typical CTRs vary hugely by platform and format, so compare against your own past campaigns rather than generic benchmarks.

CPC: cost per click

Formula: spend ÷ clicks

₹20,000 ÷ 4,000 = ₹5 CPC

CPC combines CPM and CTR: a better CTR lowers your CPC even if CPM stays the same.

Conversion rate

Formula: conversions ÷ clicks × 100

80 ÷ 4,000 × 100 = 2% conversion rate

This measures your landing page and offer as much as the ad. If CTR is healthy but conversion rate is poor, look at the page: speed, clarity, trust signals, and whether it matches the ad's promise. A slow page quietly kills conversion rate. Check yours with a speed test.

CPA: cost per acquisition

Formula: spend ÷ conversions

₹20,000 ÷ 80 = ₹250 CPA

CPA (sometimes called cost per purchase or cost per lead) is often the most useful single number, because you can compare it directly with what a customer is worth to you.

ROAS: return on ad spend

Formula: revenue ÷ spend

₹96,000 ÷ ₹20,000 = 4.8 ROAS (often written 4.8x or 480%)

ROAS sounds like profit, but it isn't. It ignores product costs, shipping, payment fees and returns.

The number that actually matters: profit

Say your gross margin (after product cost, shipping and fees) is 40%. Then:

• Gross profit from the sales: ₹96,000 × 40% = ₹38,400
• Minus ad spend: ₹38,400 − ₹20,000 = ₹18,400 profit

Your break-even ROAS is 1 ÷ margin. At 40% margin, that's 1 ÷ 0.4 = 2.5. Below a ROAS of 2.5 you lose money on the first sale, and above it you make money.

If customers come back and buy again, a higher CPA can still be worth it. That's where customer lifetime value (LTV) comes in: the total profit you expect from a customer over time.

Reading the numbers together

• Low CTR points to the ad itself: creative, message or audience.
• Good CTR, low conversion rate points to the landing page, the offer or a mismatch between them.
• Good conversion rate, high CPA means reach is expensive, so test broader audiences or new placements.
• Good ROAS but no profit means your margin is thinner than you think. Check the break-even ROAS.

One warning about attribution

Each ad platform tends to credit itself for conversions, and different platforms often claim the same sale. Compare platform-reported results with what your store or CRM actually recorded. When they disagree, your own sales data is the source of truth.