How long does a letter take to arrive? Between 30 minutes and about two and a quarter days.
That is the entire range. Letterway is a pen-pal app where a letter crosses real distance at a fixed speed, so a letter to someone across your own city arrives in half an hour, and a letter to the point directly opposite you on the globe takes 53 hours. Nothing else moves the number — not what you paid, not how long the letter is, not who you are.
This post is the arithmetic. If you want the reasoning behind having a delay at all, that is a separate argument and it lives in why a letter should take time to arrive.
The formula
Two constants, and the only variable is how far apart the two of you are:
travel time = 30 minutes + ( distance in km ÷ 380 km/h )
Thirty minutes of handling, then one hour for every 380 kilometres. That is the whole model. There is no rounding to business days, no weekend, no customs, no sorting office having a bad week.
That half-hour is not padding. At a flat 380 km/h with nothing added, a letter across one city arrives in about two minutes, which is a chat app with stationery. The thirty minutes is what makes a short journey still feel like post.
How long a letter takes on real routes
Every figure below is generated by the same functions the app uses, on the same city coordinates:
| Route | Distance | Arrives in |
|---|---|---|
| Islamabad → Lahore | 270 km | 1.2 hours |
| London → Berlin | 930 km | 2.9 hours |
| Karachi → Lahore | 1,000 km | 3.1 hours |
| Karachi → Nairobi | 4,400 km | 12.1 hours |
| London → New York | 5,600 km | 15.2 hours |
| Lahore → London | 6,300 km | 17.1 hours |
| Tokyo → Berlin | 8,900 km | 23.9 hours |
| London → Melbourne | 16,900 km | 45.0 hours |
| Tokyo → São Paulo | 18,500 km | 49.2 hours |
The longest journey physically available is a little over 20,000 km — two points directly opposite each other on the globe — which comes to 53 hours, or 2.2 days. Nothing in Letterway can take longer than that.
How the distance is measured
Along the surface of a sphere, not through it. The app computes the great-circle distance between two points using the haversine formula, with a mean Earth radius of 6,371 km. It is the same calculation a navigator would use, and it is accurate to within about half a percent — the Earth is not a perfect sphere, and for deciding whether a letter takes 25 or 26 hours that is well inside the noise.
Two things about it matter more than the maths.
The distance is measured once, and then frozen. When you send a letter, the distance and the travel time are written onto that letter and never recalculated. If either of you moves house next week, the letter in the air keeps the journey it actually made.
It is never measured from the pins on the map. The dot representing a person on the Atlas is deliberately displaced by up to 25 km from where they actually are, and it exists only to draw an arc. The real distance is computed from precise coordinates that are never sent to anybody's browser, and then rounded before it is shown to you — to the nearest 10 km under a thousand, and the nearest 100 km above it. A metre-accurate distance read from two accounts would triangulate a home address. That is why "6,300 km" and never "6,314 km".
Why 380 km/h
Honestly: because it produces the range we wanted.
380 puts a letter between neighbouring cities at an hour or two, most intercontinental letters inside a day, and the absolute worst case under two and a half. Long enough that a letter is a journey. Short enough that a correspondence does not die of old age waiting for one.
It started at 225, which put a letter from Pakistan to the east coast of America at fifty-two hours — a full exchange took four and a half days, and the first thing a new person experienced was two days of nothing. That is a real cost and it was not buying anything the shorter wait does not also buy.
It is not derived from an aircraft or a postal service. There was no physics involved. What matters is not the number but that there is exactly one of it:
- Distance is the only thing that costs time.
- You cannot pay to arrive sooner. There is no priority post, no boost, no ad to watch.
- Every letter on every plan travels at the same speed.
The moment delivery speed becomes purchasable, the medium stops being about distance and starts being about who spent money.
How this compares to the real thing
Here is the joke at the centre of the product: the slow app is faster than the post.
Royal Mail's International Standard service quotes 3 to 5 working days to Europe and 6 to 7 working days worldwide. Their International Economy service quotes up to eight weeks to Asia and Africa, and up to twelve to Australia. Letterway's slowest possible letter, to a point directly opposite you on the globe, is 2.2 days.
Going further back makes it stranger. The world's first official airmail flight was on 18 February 1911, when Henri Pequet flew 6,500 letters 13 km from Allahabad to Naini in thirteen minutes — about 60 km/h. Letterway would take 32 minutes over that same 13 km, because of the half-hour of handling. We are, on that specific route, slower than a 1911 biplane.
We like both of these facts. A letter that takes a day is not a re-enactment of the post. It is a pace chosen on purpose, and it happens to sit between the aeroplane and the sorting office.
The number can change. Your letter cannot.
380 lives in a settings table in the database, not in the code. It can be changed with one call, and it already has been once — it used to be 225.
When it changes, every letter still in the air changes with it. That is deliberate, and it took an argument to get right. The alternative — freezing each letter's speed at the moment it was posted — sounds safer and quietly breaks the rule at the top of this post: a letter posted on Tuesday and one posted on Wednesday would fly the same route at different speeds, and when you posted would become a second thing that costs time. Two people comparing notes on the same route would get different answers with nothing to explain the difference.
So a retune moves everything still flying. What it does not touch is anything that has already landed — that journey happened, and rewriting it would be inventing history. And the countdown only ever moves when somebody deliberately moves it: it is a stored timestamp, not a live calculation off a settings row, so it cannot drift on its own.
Common questions
Can I pay to make a letter arrive faster?
No, and this is not a feature we are keeping back for a paid tier. Every letter travels at 380 km/h regardless of plan.
Does a longer letter take longer to arrive?
No. Length has no effect on travel time — only distance does. A first letter is capped at 220 words, but that is about how a correspondence starts, not about how fast it moves.
What happens if the other person deletes their account mid-flight?
A letter addressed to someone who has left is withheld, and the app says so rather than running the countdown down to an arrival that will not happen. A letter they had already sent you is not affected — it lands on time.
Can I see where my letter is right now?
Yes. Every letter in transit shows how far it has come and how long is left, and the Atlas draws the arc with the letter's actual position on it. The maps are drawn from open data rather than a stock SDK.
Is the timer paused overnight or at weekends?
No. It is a plain countdown in real time. A letter posted on Friday evening keeps travelling all weekend.
Working out how long your own letter takes
Take the distance between you and the person you are writing to, divide by 380, and add half an hour. A rough version for the head: half an hour to start, then just under three hours per 1,000 km.
If you are about to write your first one and are staring at a blank page, we wrote a guide for that too — what to write in your first letter to a pen pal.
Letterway is in development. If a letter that takes a day to cross an ocean sounds like a good idea rather than a bad one, join the waitlist — invitations go out in the order people join.