Countries · Finland

Finland: how to write an address

Address verification puts every address into the postal form of the country and checks it against the national address register: street, house number, postcode, coordinates. Here you'll find how to write an address there, what we check and three before-and-after examples.

Verify an address API documentation

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How address verification and duplicate detection work.

What an address looks like

House number·after the street (“Hauptstraße 5”)
Postcode·12345; the country prefix in front (D-, F-, CH-) is removed
City·in capitals, in its local name
Country·country line and ISO code, in the reader's language

Finland is bilingual: the coastal cities have a Finnish and a Swedish name (Helsinki/Helsingfors, Turku/Åbo) and so do the streets (“Unioninkatu”/“Unionsgatan”); the register keeps both. The street type is attached to the name and stays lower case (“katu”, “tie”), “k.” expands to “katu”. The postcode has five digits; the house number can be a range (“14-16”).

What we verify

Addresses: the whole country · postcodes: 100% · data as of 19 Oct 2026.

Street·exists in the municipality, written in full and in the register's spelling; abbreviations are expanded in the country's language
House number·exists on that street; if the street exists and the number does not, the outcome flags it
Postcode·confirmed or filled in by the register, in the country's format
Coordinates·latitude and longitude of the house number, with the precision declared
Autocomplete·the street completes as you type, from the register; the house number and the postcode come with the selection (API)
WooCommerce · PrestaShop·autocomplete at checkout and order verification with the plugins

Rakennusten osoitetiedot © Suomen ympäristökeskus (Syke), Ryhti — CC BY 4.0; postinumerot © Posti Oy · CC BY 4.0

Before and after

Three addresses written the way people write them — abbreviated, without postcode, in lower case — and how they come out: public buildings and streets of the city centre, verified down to the house number.

unioninkatu 36, FI-00170 Helsinki → Unioninkatu 36
00170 HELSINKI postcode fixed · coordinates of the house number
aleksis kiven k. 14, 33100 tampere → Aleksis Kiven katu 14
33210 TAMPERE postcode fixed · street written in full · coordinates of the house number
aurakatu 2, 20100 turku → Aurakatu 2
20100 TURKU coordinates of the house number

With the API

The same endpoint as every country: country_code is enough. The response carries the address in postal form, the outcome with the changes, and where the register is in service the coordinates, the municipality code and the district. Everything in the API documentation.

curl -X POST https://www.radaraddress.com/api/v1/contact \
  -H 'Authorization: Bearer YOUR_TOKEN' \
  -H 'Content-Type: application/json' \
  -d '{"address":"unioninkatu 36","postcode":"FI-00170","city":"Helsinki","country_code":"FI"}'

Frequently asked questions

Do you also verify addresses that are in a file?

Yes. In batch jobs a column with the country is enough, or the country set for the whole file: every row comes back in the country's postal form, with the outcome beside it and, where the register is in service, verified down to the house number.

What happens if an address is not in the register?

The outcome flags it. If the street exists and the house number does not, it points to the house number; if the street is not found in the municipality, the address still comes out in the country's postal form, with the warning.

Where do the data come from?

From the national address register, published as open data by the country's mapping or statistics agency, which we use under the licence it requires: Rakennusten osoitetiedot © Suomen ympäristökeskus (Syke), Ryhti — CC BY 4.0; postinumerot © Posti Oy (CC BY 4.0). The register is checked every night and reloaded when the source changes.

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