Plus Code converter

What is a Plus Code?

A Plus Code, formally an Open Location Code, is a short string that names a place — 849VCWC8+X8 rather than a street and a number. The important part is that there is no database behind it. The code IS the coordinates, encoded; anyone can work out where it points with arithmetic alone, offline, with no lookup and no permission from anybody.

That matters most where addresses do not exist or are not reliable, which is a large share of the world. It is also useful for anywhere an address cannot reach: a gate in a field, a trailhead, a stall in a market, the specific corner of a large building where a delivery should go.

The scheme works by shifting latitude and longitude to be positive, then writing them in base 20 with a twenty-character alphabet, one character for latitude and the next for longitude, alternating. A plus sign goes after the eighth character. That is the whole idea — everything else is refinement.

How to use it

1. Pick a direction. Coordinates to code, or code to coordinates. The place buttons load a few real locations, including the North Pole, which is where naive implementations tend to break.
2. Choose a length. Ten characters is the usual choice. Shorter codes name larger areas, longer ones smaller. Below ten, lengths go up in twos, because characters are read as latitude-longitude pairs.
3. Read the cell, not just the point. A code never names a point — it names a square, and the panel shows its bounds and its true size in metres at that latitude.

The part nobody mentions: the cells stop being square

Up to ten characters, each pair divides both latitude and longitude by twenty, so the cells really are square. Ten characters gives about 13.92 metres on a side at the equator, which is the figure everyone quotes.

Past ten, the scheme changes mechanism. Base twenty has run out of useful precision, so further characters use a refinement grid instead — and that grid is four columns wide by five rows tall. Each extra character therefore divides longitude by four and latitude by five, and the cells stop being square. An eleven-character code names a cell 2.78 metres tall and 3.48 metres wide at the equator: an aspect ratio of exactly five to four. By twelve characters it is twenty-five to sixteen.

So a Plus Code is more precise north-south than east-west once you go past ten characters, and by a growing margin. It is not an error, it is what the grid is; but it does mean that describing an eleven-character code as accurate to some single number of metres is wrong in one direction or the other.

There is a second, better-known effect on top of it. Lines of longitude converge toward the poles, so the width of every cell shrinks with latitude while its height does not. At sixty degrees north a ten-character cell is still 13.92 metres tall but only about half as wide. The tool computes both at whatever place you are looking at rather than quoting a single global figure.

How this was checked, and what it does not do

The specification publishes an official conformance suite, so correctness here is a score rather than an opinion. All 51 validity vectors, all 367 encoding vectors and all 420 decoding vectors pass. The invalid cases are the half that matters — a parser that accepts anything scores well on everything except the rows that are supposed to be rejected — so those are counted separately.

Two things worth knowing about the format came out of testing rather than from reading. A code longer than fifteen characters is accepted, and the surplus is ignored: a twenty-one character code names exactly the same cell as its fifteen-character prefix, so two different strings can mean one place. And the alphabet contains no vowel at all, which is deliberate — it means a code cannot accidentally spell a word in any language.

What this does not do: short codes. A code with fewer than eight characters before the plus sign has had its leading characters dropped and only means something next to a nearby town or city, so decoding one requires a place-name lookup that this page has no database for. It reports them as short rather than guessing. It also does not draw a map, because that would mean loading one from somebody else's server and telling them where you are looking.

The arithmetic is exact in the sense that matters: the encoder works in whole units of the smallest cell rather than dividing repeatedly, which is what keeps values on cell boundaries from landing in the wrong square.

Why is it free?

It is arithmetic on two numbers, running in your browser. There is no server, no map tile to fetch, and no account to create.

Nothing you type is uploaded, stored or logged — which is worth stating plainly here, because the input is a location. It never leaves the tab.