Diphthongs: ei, øy, au

A diphthong is a single vowel that glides — your mouth starts in one position and slides to another within one syllable. Norwegian has a small, fixed set of native diphthongs, and the two you will meet constantly are ei /æɪ/ and øy /œʏ/. A third, au /æʉ/, turns up in a handful of common words and many loanwords. English speakers stumble here not because diphthongs are foreign — English is full of them — but because the spellings point them toward the wrong English diphthong. This page is about gliding these correctly. Vowel length and the plain monophthongs are covered separately.

ei /æɪ/ — like English "ay" in "say"

ei glides from an open front vowel up toward /i/. The result is close to the vowel in English say, day, hey — emphatically not the "eye" sound of English my or high. The single biggest ei error is reading it as English long "i".

øy /œʏ/ — a front-rounded glide

øy has no English equivalent, which makes it the trickiest of the three. It glides from the front-rounded vowel /œ/ (the sound in ø) up toward a front-rounded /ʏ/. Keep your lips rounded throughout — that rounding is what distinguishes it from ei. English speakers tend to unround it into something like "oy" (as in boy) or collapse it to "ay"; the real sound stays rounded from start to finish.

au /æʉ/ — central-to-u glide

au is spelled like English "ow/aw" but pronounced quite differently: it glides from the open front /æ/ toward the rounded central Norwegian /ʉ/. The danger is reading it as English "aw" (as in law) or "ow" (as in cow). It is neither; the second half rounds toward Norwegian u. Outside a few core words, au appears mostly in loanwords and month/name vocabulary.

Minor diphthongs: ai and oi

Two more spellings appear in a small set of words, mostly interjections, names and loans. ai /ɑɪ/ and oi /ɔɪ/ behave roughly as you would expect from the letters.

These are peripheral; the everyday workhorses are ei and øy, with au a step behind.

Diphthong vs. monophthong: a style and dialect signal

Here is the distinguishing insight. Many words exist in two forms — a diphthong form and a monophthong (plain long vowel) form — and the choice is not random. It reflects both dialect and written style.

Across regions, many dialects monophthongise these diphthongs. In Bergen and parts of the East, stein may come out as "steen", and a speaker may say sten where another says stein. So a learner will genuinely hear the "same" word both ways depending on who is talking — tie this to the broader regional picture, where each dialect's vowel habits are mapped out.

In writing, Bokmål often allows both the diphthong and the monophthong spelling, and choosing between them is a radical-vs-conservative style decision:

Both stein and sten are correct Norwegian; they differ in register and flavour, not in meaning. Stein feels more everyday and more "Norwegian"; sten feels more conservative, formal or literary, reflecting the Danish-influenced tradition in Bokmål. (formal/literary) for the monophthong; (informal) leaning for the diphthong. So when you hear or read these pairs, you are reading a style signal as much as a sound — a preview of the radical-vs-conservative Bokmål distinction, which is detailed on its own page.

Common Mistakes

Key Takeaways

• ei /æɪ/ = English "ay" in say, never "eye": nei, hei, vei, stein.
• øy /œʏ/ = a front-rounded glide with no English equivalent: øy, høy, gøy, røyk — keep the lips rounded.
• au /æʉ/ glides toward Norwegian u, not English "aw": sau, august, tau.
• Many dialects monophthongise these, so you'll hear stein as "steen" in places — a regional, not an error.
• The stein/sten type pair is a style signal: diphthong = modern/colloquial, monophthong = conservative/literary, same meaning.