CPA vs ROAS: Which Target Should You Optimise For?

Two terms dominate paid advertising targets: CPA and ROAS. Both help you judge whether ads are worth the money, but they answer different questions. Picking the wrong one can push an automated campaign in a direction that looks efficient and still loses money.

The definitions

• CPA (cost per acquisition): how much you spend to get one conversion, such as a lead, sign-up or sale. Formula: ad spend divided by conversions.
• ROAS (return on ad spend): how much revenue you get for each rupee of ad spend. Formula: revenue from ads divided by ad spend.

A simple illustration with made-up numbers

This is hypothetical. Suppose you spend Rs 10,000 and get 20 sales.

• CPA is Rs 500 per sale.
• If total revenue from those sales is Rs 40,000, ROAS is 4, meaning Rs 4 of revenue per Rs 1 spent.

If the same 20 sales had brought only Rs 20,000 revenue, CPA would still be Rs 500 but ROAS would be 2. Same CPA, very different business.

When CPA fits

• Every conversion is worth about the same, as with a fixed-fee service or a standard lead.
• You are generating leads where value is known only later.
• Your focus is lead volume at a controlled cost.

For leads, remember that cheap leads are not always good. Check lead quality scoring for ads.

When ROAS fits

• Order values vary a lot, as in online stores with different price points.
• You can pass accurate revenue values into your ad platform.
• You care about revenue efficiency across a catalogue.

What neither tells you

Both ignore your costs. A ROAS of 3 sounds healthy, but if your margin is thin, after product cost, shipping and fees you could still lose money. Work out your break-even ROAS from your margin. If profit per sale is a quarter of revenue, you need a ROAS above 4 just to break even on the first sale, ignoring other costs. The marketing ROI calculation guide walks through this.

Include customer value

If customers buy again, a break-even first order might still be a good deal. See the customer lifetime value guide for how to factor that in. Be careful: estimate repeat behaviour from your own data, not hopes.

How it connects to bidding

Platforms offer automated strategies that aim for a target CPA or target ROAS. They need reliable conversion data and enough volume to work. Set targets close to your real results, not wishful numbers. More on this in bid strategies explained.