How to Set an Ad Budget and Measure ROAS
How much should you spend on ads, and how do you know whether that spend is working? The answer starts with two numbers most small businesses never calculate: what a customer is worth and the return you need from every ad dollar just to break even. This explainer shows you how to work out both.
Key takeaways
- ROAS (return on ad spend) is revenue from ads divided by ad spend. A ROAS of 4 means $4 of revenue for every $1 spent.
- A good ROAS depends on your margins. Your break-even ROAS is 1 divided by your gross margin.
- Set your budget from the bottom up: what you can afford to pay for a customer, times the number of customers you want, plus a learning budget.
- ROAS measures revenue, not profit, and platforms report it using their own attribution rules. Always check it against your own sales data.
Ask a small business owner how their ads are doing and you will often hear about clicks, reach or likes. Those numbers are easy to see in the dashboard, but none of them pays the rent. What matters is whether the money you put into ads comes back as profit.
This explainer gives you the simple math for setting a budget and judging results. It applies to Google Ads, Facebook and Instagram ads, and most other paid channels. It builds on ideas from our simple two-page marketing plan, where your ad budget should sit alongside your other marketing goals.
What ROAS means
Return on ad spend is the revenue you can attribute to your ads divided by what you spent on them.
ROAS = revenue from ads ÷ ad spend
If you spend $500 on ads in a month and those ads lead to $2,000 in sales, your ROAS is 4, often written as 4:1, 4x or 400%. Google Ads and Meta Ads Manager can both report ROAS automatically if you track purchase values with conversion tracking.
ROAS is popular because it is easy to understand and compare across campaigns. But on its own, it does not tell you whether you are making money. For that you need your margins.
Break-even ROAS: the number that matters most
Every sale has costs: the product itself, packaging, delivery, payment fees and so on. What is left after those direct costs is your gross profit. If your ads cost more than the gross profit they produce, you lose money on each sale, however good the ROAS looks.
| Gross margin | Break-even ROAS | What it means |
|---|---|---|
| 20% | 5.0 | You need $5 in revenue per $1 of ads to break even |
| 30% | 3.3 | You need about $3.33 per $1 |
| 40% | 2.5 | You need $2.50 per $1 |
| 60% | 1.7 | You need about $1.67 per $1 |
| 80% | 1.25 | You need $1.25 per $1 |
This is why there is no universal "good ROAS." A software company with 80% margins can be very profitable at a ROAS of 2, while a reseller with 20% margins loses money at a ROAS of 4. If you are unsure of your margins, our guide to margin, markup and break-even explains how to calculate them.
Common mistake
Comparing your ROAS to a benchmark from an article or an agency pitch. Benchmarks ignore your margins, your prices and your repeat purchase rate. The only meaningful target is the one built from your own numbers.
When ROAS is not enough
ROAS works best for e-commerce, where each sale has a clear value at checkout. It is less useful in other cases:
- Lead generation: if ads produce calls or form fills, track cost per lead and then cost per customer, using your close rate. A plumber who wins 1 in 3 quotes needs to know what each won job costs.
- Repeat purchases: a first order may barely break even, but a customer who returns every month is worth far more. Use customer lifetime value instead of first-order revenue. Our article on calculating customer lifetime value covers this.
- Brand and awareness campaigns: these may not produce direct sales in the platform's attribution window but can lift sales over time. Judge them on reach, cost per thousand impressions and changes in branded searches or direct visits.
A related metric is CAC (customer acquisition cost): total marketing spend divided by new customers. And MER (marketing efficiency ratio), sometimes called blended ROAS, divides total revenue by total ad spend across all channels. MER avoids arguments over which platform gets credit and is useful for checking the big picture.
You do not need all of these metrics at once. Pick the one that best matches how your business makes money: ROAS for online stores with clear order values, cost per customer for lead-based services, and lifetime value for subscriptions or frequent repeat buyers. Then add MER as a monthly cross-check, so a single platform's dashboard never becomes your only source of truth.
How to set an ad budget step by step
Many guides suggest spending a fixed percentage of revenue on marketing. Percentages can be a sanity check, but they ignore whether ads actually pay back. A bottom-up approach ties the budget to customers.
- Calculate gross profit per customer. Use first-order profit if most customers buy once, or a conservative lifetime gross profit if they come back.
- Decide your maximum acquisition cost. Choose how much of that profit you are willing to spend to win a customer. Spending all of it means breaking even on ads; spending less leaves profit.
- Set a customer goal. Decide how many new customers you want from ads this month, based on what you can actually serve.
- Multiply. Maximum acquisition cost times customer goal gives you a target monthly budget.
- Add a learning budget. New campaigns rarely hit target costs immediately. Set aside a fixed amount you can afford to spend on testing without expecting a return.
- Check cash flow. Ad platforms charge quickly, but customers may pay later. Make sure you can fund the spend for at least two or three months. Our small business budget guide can help you fit it in.
Worked example (hypothetical)
Suppose an online tea shop has an average first order of $50 at a 50% gross margin, so each first order brings $25 of gross profit. The owner's records suggest that a typical customer orders about three times a year, so first-year gross profit is roughly $75. She decides she will pay up to $30 to win a customer, leaving room for profit and for mistakes in her estimates. She wants 40 new customers a month, so her target budget is $30 times 40, or $1,200, plus a $300 learning budget in the first month. Her break-even ROAS on first orders is 1 ÷ 0.5, or 2. If her campaigns run at a ROAS of 1.7 on first orders, they lose a little up front, but because she knows repeat orders follow, she may accept that while tracking whether customers really return.
Measuring ROAS accurately
ROAS is only as good as the data behind it. Keep these points in mind:
- Track purchase values, not just conversions. Set up conversion tracking that passes the order value, so the platform can calculate ROAS.
- Understand attribution. Each platform decides which sales to credit using its own attribution model and time window. Google and Meta may both claim the same sale, so adding their reported revenue together usually overstates results.
- Account for refunds and cancellations. Platform ROAS uses the value at checkout. Adjust for returns using your own records.
- Watch for tracking gaps. Consent requirements, ad blockers and device privacy settings mean some sales are never reported. Compare total sales in your store or accounts with platform figures each month.
- Remember taxes and fees. Some countries add VAT or other taxes to ad invoices, and Google adds regulatory fees in certain countries. Include these in your true ad spend.
Pro tip
Create a one-page monthly ad report with five lines: total ad spend, new customers, cost per customer, platform-reported ROAS and your blended revenue divided by total ad spend. Over six months, this simple sheet will tell you more than any dashboard.
When to raise, hold or cut the budget
Signs you can increase spend
- ROAS or cost per customer is comfortably better than break-even
- Results have held steady for several weeks
- You have the capacity and cash flow to serve more customers
Signs to hold or cut
- ROAS sits below break-even with no repeat-purchase case
- Results swing wildly from week to week
- Platform figures do not match your own sales records
Increase budgets gradually. Large, sudden jumps can push platforms into less efficient audiences and, on Meta, can restart the learning phase. Many advertisers raise budgets in modest steps and watch results for a week before the next increase.
Your ad budget checklist
- Calculate gross margin and gross profit per customer
- Work out your break-even ROAS as 1 divided by gross margin
- Choose a maximum acquisition cost below gross profit per customer
- Set a monthly budget from your customer goal plus a learning budget
- Set up conversion tracking that passes order values
- Compare platform-reported results with your own sales each month
- Adjust budgets in small steps based on several weeks of data
Frequently asked questions
What is a good ROAS for a small business?
A good ROAS is one comfortably above your break-even ROAS. With a 50% gross margin, anything above 2 contributes profit before other costs. With a 25% margin, you need more than 4. Calculate your own threshold rather than using industry averages.
Is ROAS the same as ROI?
No. ROAS compares revenue with ad spend only. ROI (return on investment) compares profit with the total investment, including product costs, fees, staff time and agency costs. A campaign can have a healthy ROAS and still produce a negative ROI.
Should I set a daily or monthly ad budget?
Plan monthly, run daily. Decide your monthly budget based on your goals and cash flow, then divide it into daily campaign budgets. Platforms like Google Ads may spend more on some days and less on others but manage spend against a monthly limit.
How long should I test before judging ROAS?
Long enough to collect a meaningful number of conversions, which for many small businesses means several weeks. Judging a campaign on a few days of data often leads to cutting campaigns that would have improved.
Related reading
The bottom line
Ad budgets should come from your numbers, not guesswork or platform suggestions. Know your gross margin, calculate your break-even ROAS, decide what you can afford to pay for a customer and build your budget from there. Then measure results against your own sales records, adjust gradually and judge every campaign by the profit it brings in, not the clicks it collects.
