Three numbers decide whether a mailing pays off: response rate, cost per acquisition, and ROI. Here's the math — with honest, hedged ranges — and the levers that move it.
Run the Numbers — Free ROI Calculator"Direct mail is expensive" and "direct mail works great" are both useless on their own. The question a small-business owner actually needs answered is simpler: for every dollar I spend mailing, how many dollars come back? That's return on investment, and you get to it through two intermediate numbers — response rate and cost per acquisition.
The share of people who got the mail and took the action you wanted — called, scanned, booked, or bought.
Total mailing spend divided by the number of new customers it produced. The real "what did one customer cost me?" figure.
Revenue (or profit) generated minus what you spent, divided by what you spent. The dollars-back-per-dollar-in number.
Walk it once and you'll never be intimidated by a direct-mail quote again. We'll use round, illustrative numbers — swap in your own to see your real picture.
Count the responses, divide by the number of pieces mailed.
Industry studies tend to put response to an existing house list in the low-to-mid single digits (often cited around 3–6%) and cold prospect lists lower (often ~1–2%).1 These are estimates — your list, offer, and follow-up drive the real number.
Not everyone who responds becomes a paying customer, so CPA divides total spend by customers won, not responses.
Use a close rate you can actually defend. If you don't know it yet, model a range (say 40–70%) and look at both ends.
Now bring in what a customer is worth. Use a customer's value to you — a single sale, or their lifetime value if they tend to come back.
That headline multiple is entirely a function of the inputs above — it is not a guaranteed PostKnock result. Halve the response rate or the customer value and the picture changes fast. The point of the math is to find the inputs where the mailing is worth running, not to chase one number.
Plug in your list size, response rate, close rate, and customer value — the free ROI calculator does response rate → CPA → ROI for you, and shows the break-even point.
Open the Free ROI Calculator →Before you obsess over a big ROI multiple, find the smallest result that makes the mailing worth it. Break-even tells you how many customers you need just to get your money back.
If mailing 500 cards only needs roughly one or two new customers to pay for itself, the downside is small and the math is forgiving. When break-even needs dozens of customers, that's your signal to fix the offer, tighten the list, or rethink the spend — before you mail.
Every lever pulls on one of the three numbers above. The two with the most leverage for a small business: measure it (so you stop guessing) and add a second touch (so one mailing isn't your only shot).
Measurement and follow-up are exactly where most "just print and mail it" tools stop. PostKnock builds both into the campaign.
Add a QR code to any postcard linking to your booking page or offer. A scan is a measurable signal the card got noticed — it turns "did the mail do anything?" into a number you can divide.
Playbooks set UTM parameters on the destination URL, so visits from the card show up labeled in your own web analytics. That's attribution without any integration — the data lands in the analytics you already run.
A few days after delivery, the built-in Call Queue (a Pro feature) fills with the people who got the card. Your front desk works it with the wave's pre-loaded script and logs each outcome. A second, human touch is the single biggest ROI lever most mailings never use.
Stack them across a multi-wave playbook (up to 5 waves) and non-responders roll forward automatically — so your spend keeps working instead of evaporating after one drop. The math compounds: more responses per dollar mailed is exactly how response rate climbs and CPA falls.
Per-piece pricing is transparent and pay-from-wallet — you only pay when you send, so your "spend" input is never a mystery.
Single-wave postcard campaigns · Unlimited contacts · From $1.05/piece
Everything in Free + the Call Queue & multi-wave sequences · From $0.79/piece
Per-piece pricing includes printing + USPS First-Class postage. Pro is $99/mo or $799/yr. See full pricing →
Tools and guides to turn the math into a campaign:
Enter your list size, response rate, close rate, and customer value — get CPA, ROI, and break-even instantly.
Open the calculator →
A deeper look at what drives postcard returns for small service businesses.
Read the guide →
Win back lapsed customers — the cheapest, highest-response list you can mail to.
See how it works →
Blanket a neighborhood when prospecting beats targeting a known list.
Explore EDDM →
Take the revenue (or profit) the mailing generated, subtract what you spent, then divide by what you spent. So ROI = (revenue minus spend) divided by spend. To get there you usually work through two earlier numbers first: response rate (responses divided by pieces mailed) and cost per acquisition (total spend divided by new customers won). The free PostKnock ROI calculator runs all three for you.
It varies widely by list quality, offer, and follow-up, so treat any figure as an estimate. Industry studies typically report response to an existing house list in the low-to-mid single digits, often cited around 3 to 6 percent, and cold prospect lists lower, often around 1 to 2 percent. Lapsed customers tend to respond better than cold prospects because they already know you, and adding a phone follow-up gives non-responders a second touch.
CPA is your total mailing spend divided by the number of new customers it produced, not the number of responses. For example, mailing 500 cards at $0.79 each is $395 in spend; if that yields 25 responses and you close 60 percent of them, that's 15 customers, or about $26 per new customer. Always use a close rate you can defend, or model a range if you do not know it yet.
Two ways, both built in. Add a QR code that links to your booking page or offer, so scans are a measurable response signal. And playbooks add UTM parameters to the destination link, so the traffic shows up labeled in your own web analytics. For the people who do not scan, logged outcomes from the Call Queue tell you how the phone follow-up went. PostKnock does not connect to or sync with your other software; attribution lands in the analytics you already run.
A single mail drop only gets one shot at a response. A few days after delivery, PostKnock's built-in Call Queue (a Pro feature) fills with the people who received the card, and your own staff works it using the wave's pre-loaded script. That second, human touch lifts the share of recipients who take action, which raises response rate and lowers cost per acquisition. Non-responders can roll forward into the next wave of a multi-wave playbook, up to five waves.
A 4x6 postcard starts at $1.05 on the Free plan and drops to $0.79 on Pro, with printing and USPS First-Class postage included in that per-piece price. You pay from your wallet only for what you send, with no setup fees, no minimums, and no contracts. Pro is $99/mo or $799/yr and adds the Call Queue and multi-wave sequences. Postcards also come in 6x9 and 6x11 sizes.
Yes. The free PostKnock ROI calculator takes your list size, response rate, close rate, and customer value, then shows response rate, cost per acquisition, ROI, and break-even. It runs in your browser, requires no account, and uses round, illustrative defaults you can replace with your own numbers.
Run the free ROI calculator, pick a playbook, and launch — QR tracking, UTMs, and the Call Queue do the measuring. Start free; you only pay when you send.
Start Free — No Credit Card1 Direct-mail response-rate ranges are drawn from general industry benchmarks (e.g. ANA / DMA Response Rate Report coverage). Figures are estimates that vary widely by list, offer, and follow-up — presented here as ranges, not guarantees. The ROI, CPA, and break-even examples on this page use round, illustrative inputs to show the math; they are not PostKnock performance claims.