There's a number that gets repeated in every DTC Slack: an SMS subscriber is worth more than an email subscriber. Usually the multiple quoted is somewhere between 3x and 6x. It's not wrong. But it's quoted without the cost side, and the cost side is where the decision actually lives — because SMS costs money per send and email effectively doesn't.
So let's do the whole equation. Not "SMS converts better," which is true but useless for budgeting. The actual question: for every dollar you'd otherwise spend acquiring and messaging a contact, which channel returns more — and at what list size does that flip?
Full disclosure: I work for Ready, an SMS platform. I'm going to show you math where email wins in specific cases, because it does. If I only wanted to sell you texts I'd leave that part out.
The per-contact revenue gap is real — start there
Let's ground the "6x" claim in something you can recompute for your own store.
Take a mid-sized DTC brand sending a promo to 20,000 contacts on each list:
- Email: ~35% open rate, ~2.5% click, ~1.2% of openers convert to purchase → roughly 240 orders at a $60 AOV = $14,400 per campaign.
- SMS: opted-in lists get read at something close to 90%+ (framed as an industry approximation, not a promise), ~15% click, ~4% of recipients convert → roughly 800 orders × $60 = $48,000 per campaign.
That's a 3.3x revenue gap on the same list size, same offer. Push the SMS conversion assumptions to the top of the honest range and you land near the 6x figure people love to cite. Both numbers are defensible depending on your list quality.
But notice what I did: I sent to the same count on both lists. That never happens in real life, and it's the first place the story gets complicated.
Now subtract the send cost email doesn't have
Email's marginal cost per send rounds to zero. Your ESP charges a monthly subscription based on list size, but hitting "send" on a campaign costs you nothing incremental. SMS is the opposite: every segment is metered.
On Ready's Standard tier, that's $0.02/segment + $0.0045 carrier pass-through = $0.0245 all-in. And "one text" often isn't one segment. A plain 160-character GSM-7 message is one segment. Add an emoji and the ceiling drops to 70 characters — a 175-character promo with a 🎉 becomes three unicode segments.
Here's that 20,000-contact SMS blast, priced honestly at 3 segments:
`` 20,000 contacts × 3 segments × $0.0245 = $1,470 per send ``
So the SMS campaign nets $48,000 − $1,470 = $46,530. The email campaign nets basically its full $14,400 (minus a flat monthly ESP fee you're paying regardless).
SMS still wins the head-to-head badly. The send cost is real but it's roughly 3% of the revenue it drives. That's not the problem. The problem is list size — and decay.
List size: SMS lists are smaller, and that's structural
You will never grow an SMS list to the size of your email list. Email opt-in is one field and a soft ask. SMS opt-in requires explicit consent, usually double opt-in, and people guard their phone number harder than their inbox.
A realistic split for a brand with 100,000 email subscribers might be a 12,000–18,000 SMS list. If you run confirmed double opt-in, you lose another 20–30% of sign-ups at the confirmation step — which sounds like a leak until you look at what survives it. I wrote about that tradeoff in double opt-in and revenue per contact: the people who confirm convert dramatically better, so the smaller confirmed list often out-earns the bigger unconfirmed one.
So the honest comparison isn't "same list, both channels." It's:
| SMS | ||
|---|---|---|
| Reachable contacts | 100,000 | 15,000 |
| Read rate (approx) | ~35% opens | ~90%+ |
| Effective reach | ~35,000 | ~13,500 |
| Cost per campaign (3-seg promo) | ~$0 marginal | ~$1,100 |
| Revenue/campaign (same assumptions above) | ~$72,000 | ~$36,000 |
At these list sizes email out-earns SMS per campaign — not because it's better per contact, but because there are 6.6x more contacts on it. Per contact, SMS still wins. In aggregate, the bigger list wins until SMS closes the size gap.
Deliverability and decay cut deeper on email over time
The revenue-per-contact story tilts back toward SMS once you factor decay, because email lists rot faster than they look.
- Email list decay: roughly 20–25% of an email list goes stale per year — people abandon addresses, change jobs, or your sends quietly start landing in Promotions/spam. "Deliverable" and "delivered to the primary inbox" are different numbers, and the gap widens as your sender reputation drifts.
- SMS decay: much slower. Phone numbers persist for years, and opt-out is explicit, so your "list" is a truer count of reachable humans. When someone texts STOP, they're gone — no gray area. On Ready that STOP is honored automatically and propagates across campaigns so you can't accidentally re-message them.
The practical effect: your stated email list is inflated by dead weight you're still paying your ESP to store. Your stated SMS list is closer to real. So the per reachable contact gap is wider than the raw counts suggest — you're comparing a partly-fictional email number against an honest SMS one.
The honest crossover: where SMS budget beats email budget
Put the pieces together and there's a defensible rule for allocating the next marketing dollar.
Email wins when:
- Your SMS list is under ~5,000 and you have a large, still-engaged email list.
- Your offer is content-heavy — long-form storytelling, editorial, multi-product — where SMS's 160 characters can't carry the message.
- Your margins are thin enough that $1,000+ per SMS blast changes the P&L.
SMS wins when:
- You need the message read now — flash sale, back-in-stock, shipping/appointment updates, abandoned checkout inside the first hour.
- Your SMS list has cleared double opt-in, so conversion sits at the top of the range.
- You're sending short, transactional, or time-boxed offers where 1–2 segments does the whole job and the per-send cost stays under 3–4% of revenue.
The crossover isn't a single list size — it's per-use-case. Most stores I'd advise to run both, and to stop treating the budgets as competing. Email carries the long, cheap, top-of-funnel and re-engagement work. SMS carries the urgent, high-intent, time-sensitive moments where a 90% read rate is worth the metered cost.
Where cross-channel actually saves you money
The biggest waste I see isn't picking the wrong channel — it's sending both blindly. You blast the whole SMS list and the whole email list the same offer, paying $1,470 to text people who would've converted from a free email anyway.
Two things fix that:
- Segment before you send. Text only the segment where immediacy changes the outcome — cart abandoners in the last 60 minutes, VIPs, back-in-stock waitlists. Let email cover everyone else. If a 15,000-contact SMS blast is $1,100, sending to the 3,000 who actually need urgency is $220. Same revenue lift on the high-intent group, one-fifth the cost.
- Keep the reply thread in one place. When someone texts back "does this ship to Canada?" and later opens your email, those shouldn't be two disconnected conversations. Ready's unified inbox lands inbound replies in-app (and syncs into GoHighLevel for connected accounts), so the SMS conversation isn't a black hole your support team can't see.
Keep the cost side legible, too. Ready bills prepaid credits through Stripe with the $0.0045 carrier fee itemized separately rather than baked into a marked-up per-message rate, so when you reconcile SMS spend against revenue you're reading a real number, not a bundled one. If you cross 50,000 segments in a calendar month the Growth rate applies automatically — $0.016/segment — but read that post before you assume your blended cost drops to $0.016, because the first 50K still bills at Standard.
The practical takeaway
Per contact, an opted-in SMS subscriber genuinely is worth several times an email subscriber — the read rate and conversion gap are real, and the send cost is a small fraction of the revenue when your messages stay short.
But "worth 6x per contact" doesn't mean "spend everything on SMS." Your SMS list will always be smaller, your email list will always be cheaper to send to, and email decay quietly overstates its own reach. The right move is almost never one channel. It's email for breadth and re-engagement, SMS for urgency and intent, and tight segmentation so you're not paying to text people a free email would have converted.
If you want to run the numbers on your own list before shifting budget, you get 2,500 free credits, no card required — enough to test a real segment of your SMS list against an email control and see which side of the crossover you're actually on. Start here and check your own math instead of trusting the 6x on a slide.