Carrier roaming, a local SIM, or a travel eSIM. Those are the options, and most "which is cheapest" articles pick a winner by quoting a headline price and stopping there. The trouble is that the three options are priced on completely different models — per day, per bundle, and per megabyte — so a single headline number tells you almost nothing until you know your own usage. This piece does the math properly, with rates you can check, and ends with a rule you can apply to your own trip.
We have shorter takes on two of the pairings already — eSIM vs roaming and eSIM vs local SIM. This is the three-way version with the numbers shown.
The variable everyone forgets: your actual usage
Cost-per-gigabyte is meaningless without knowing how many gigabytes you will use, and most people badly overestimate. A week of maps, messaging, the occasional ride-share and a bit of browsing — with hotel and café wifi filling the gaps — is often 1 to 3 GB, not the 10 GB people reflexively buy. We have a whole guide on how much data you actually need, but the short version is: the three pricing models reward different usage levels, so the right choice depends on where you land.
- Roaming is usually priced per day: a flat daily fee no matter how little you use. It rewards short trips with heavy daily use and punishes light use.
- A local SIM is priced per bundle: a fixed amount of data up front. It rewards long single-country stays with heavy use, and wastes whatever you do not finish.
- A per-MB travel eSIM is priced per megabyte: you pay for exactly what you use. It rewards light or variable use and multi-country trips, and never charges you for data you did not touch.
Roaming: the real math
The simplest and usually the most expensive. Many major carriers sell a roaming day pass in the rough neighbourhood of $10 to $12 per day (it varies by carrier, plan, and destination — check your own). The cost model is daily fee × number of days, full stop, whether you use 50 MB or 5 GB.
For a 3-day trip with heavy daily use, $30–36 for genuine zero-setup convenience — your number keeps working, nothing to install — is a defensible deal. For a two-week trip, the same model is $140 or more, and that is where it stops making sense. Pay-as-you-go roaming with no pass is worse still: historically notorious for running into several dollars per megabyte, enough to turn a forgotten background sync into a memorable bill.
Local SIM: the real math
Buy a physical SIM on arrival and you get the cheapest per-gigabyte data in most countries — a tourist SIM is often in the $10 to $30 range for a generous chunk of data. The cost model is a fixed amount up front for a fixed bundle.
The catch is everything around the price. You have to find a shop (not always at the airport, not always open), in many countries register the SIM against your passport, navigate it in a language you may not read, physically swap out your home SIM and keep track of it, and give up your usual number while abroad. For a month in one country with heavy use, that friction is amortised over enough days to be worth it, and the local SIM often wins outright on cost. For a weekend, you will spend more of your trip buying the SIM than you will ever save.
Travel eSIM: the real math — and the split that matters
"Travel eSIM" hides two very different pricing models, and conflating them is where most comparisons go wrong.
Bundle eSIMs (the model most of the marketplaces use) sell you a fixed data pack with an expiry date — 5 GB for 15 days and so on. That is the local-SIM model in digital form: you pay for the bundle, not your usage, and unused data evaporates when it expires. Better than a local SIM on friction, identical to it on the waste problem. We dug into why this quietly overcharges light users in pay-per-MB explained.
Per-MB eSIMs — Roamzy's model — charge for exactly the data you use, at the local rate, with a balance that does not expire. Here are real current rates, which you can verify on each country page:
- Spain, Italy and most of the EU: about $1.43 per GB.
- Thailand: about $2.15 per GB.
- France: about $0.92 per GB.
- Japan: about $3.38 per GB.
- And honestly, not everywhere is cheap — Mexico runs about $3.28 per GB. The full 193-country table is public, so check your destination rather than assume.
Three worked trips
Now put real numbers through all three models. Roaming and local-SIM figures are representative ranges; the eSIM figures are exact per-MB math.
A weekend in Paris — 3 days, light use, about 1.2 GB. Roaming day pass: roughly $30–36. Local SIM: $15–20 plus an hour of your weekend finding a shop — not worth it for two days. Per-MB eSIM in France: 1.2 GB × $0.92 ≈ $1.11, installed before you land. The per-MB eSIM wins on both cost and effort, and it is not close.
Two weeks in Japan — moderate use, about 5 GB. Roaming: ~$10/day × 14 ≈ $140. Local SIM: $25–35 for a tourist data SIM. Per-MB eSIM in Japan: 5 GB × $3.38 ≈ $17. The eSIM wins comfortably, and you skipped the queue at the airport kiosk.
A month in Thailand — heavy single-country use, about 30 GB. This is the honest one. Roaming at a daily rate is absurd here ($300). A local Thai tourist SIM can be $15–25 for a large or unlimited bundle — for a long, heavy, single-country stay, the local SIM often wins on raw cost. The per-MB eSIM comes to 30 GB × $2.15 ≈ $65 — more than the local SIM, but with no shop, no passport registration, and no SIM swap. If you are optimising purely for dollars and you will be there a month using a lot, buy the local SIM. If you value the half-day and the hassle you save, the eSIM is the smaller real cost.
And the case the other two cannot serve well: a two-week multi-country trip — say Spain, Italy and France, about 6 GB across all three. A local SIM means buying two or three of them at borders; roaming means two weeks of daily fees. One per-MB eSIM bills each country at its local rate as you cross — roughly $1.43/GB in Spain and Italy, $0.92 in France — for something in the region of $10–13 total, on one balance, with nothing to swap. Multi-country is where a single global eSIM stops being a convenience and becomes the only sane option.
The decision rule
You can skip all of the above with four questions:
- Short trip (a few days) and heavy daily use, and you want zero setup? A roaming day pass is fine — you are paying a small premium for doing nothing.
- Long stay (weeks or more) in one country, heavy use, and you do not mind the friction? A local SIM is probably cheapest on raw dollars.
- Light or variable use, or more than one country, or you just want it working before you land? A per-MB travel eSIM wins on both cost and effort.
- Not sure how much you will use? That uncertainty is itself the answer — per-MB is the only model that does not make you bet. You pay for what happens, not what you guessed.
The deeper pattern: roaming and bundles both charge you for data you do not use — a flat daily rate or a safety-margin bundle. Per-MB is the only one of the three that removes the estimation game entirely, which is also, not coincidentally, what makes it the model an AI agent can reason about instead of gamble on. Check your specific destination on the price list, do the one multiplication, and you will know.