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Dutch diphthongs

A diphthong is one vowel that glides into another inside a single syllable. Dutch has three “true” diphthongs — ij/ei, ui and ou/au — plus a set of rarer semi-diphthongs formed when a long vowel glides into a w or j off-glide. Here they all are, with mouth positions and practice words.

The big three

These three account for almost all Dutch diphthongs in running text. Two of them have no English equivalent, which is why they get their own dedicated pages.

ij / ei [ɛi]

One sound, two spellings. Start at the vowel of English bed and glide up towards “ee”, lips unrounded. ijs (ice), trein (train), klein (small). Which spelling a word takes is memorised, not heard — the full story, including the schwa-pronounced -lijk ending and the capital IJ, is on the ij and ei page.

ui [œy]

The hardest vowel in Dutch and the one with no English counterpart. Round and push your lips forward, front your tongue to the “eh” area, then glide up towards “y” keeping the lips pursed throughout. huis (house), tuin (garden), uit (out). Do not let it collapse into English “ow”. Step-by-step drills are on the ui sound page.

ou / au [ɑu]

The one true diphthong English speakers already own: it is essentially the “ow” of house. Start at open “ah” and glide to “oo”. koud (cold), vrouw (woman), blauw (blue), saus (sauce). Like ij/ei, the two spellings ou and au sound identical; which one to write is fixed per word. The one caution: keep it distinct from ui — koud and a would-be *kuid must not merge.

The semi-diphthongs: long vowel + glide

Dutch forms a second family of diphthong-like sounds by adding a w-glide [u] or j-glide [i] to a long vowel. These are less frequent but appear in common words, and English speakers tend to under-pronounce the glide. Say the long vowel fully, then add a distinct off-glide.

The one that catches English speakers most is ieuw in nieuw (new): it is “nee” + a clear w, roughly “NEE-oow”, not “new”. Likewise leeuw is “LAY-oow” and mooi is “MOH-y” with a firm y at the end.

Contrast drill: keep the three big ones apart

The classic learner failure is merging ui, ou/au and even ij/ei into one English-flavoured glide. Drill them in a set:

Why Dutch writes ou where German has au

Compare Dutch boom, oog and brood with German Baum, Auge and Brot, and it looks as if Dutch simply turned the old diphthong au into a long oo. Broadly, that is right: the Germanic diphthong *au became long [oː] in Dutch in most positions, so native Dutch words inherited from it are spelled with oo, not au. So where does the modern ou/au sound come from? Mainly from three later sources:

• An l that turned into a vowel. In medieval Dutch, short a or o followed by l and a d or t became ou: the l vocalised and merged into the vowel. That is why Dutch has oud (English old, German alt), koud (cold, kalt), goud (gold, Gold), zout (salt, Salz), hout (German Holz) and schouder (shoulder).
• Old vowels before w. Before a w, older vowels and diphthongs developed into ou/au rather than oo, which gives words like vrouw (woman), houwen (to hew), dauw (dew) and blauw (blue).
• Loanwords. French and Latin borrowings bring au: saus, pauze, auto, restaurant (where au is said as [oː], the French way).

The choice between writing ou and au is a spelling convention settled over centuries, not a sound difference: ou dominates in native words (especially the old/cold/gold set), while au is typical of loanwords and a small group of native words mostly ending in -auw (blauw, gauw, lauw, flauw). Treat this as a rule of thumb; historical linguists describe the details with many qualifications. For the wider story of how Dutch and German sounds diverged, see Dutch vs German and the history of Dutch.

North and south

The diphthongs are a well-known regional tell. In the Netherlands' Randstad the big three are often pronounced with wide, lowered starting points — the so-called “Poldernederlands” tendency, where ij drifts towards [ai] and ui and ou open up noticeably. In Flanders (Belgium) and the southern Netherlands the same diphthongs are tighter, higher and sometimes barely glide at all, so ij/ei can sound almost like a long monophthong [ɛː]. Both patterns are standard; a learner is safe copying either, as long as the three stay distinct from one another. This is part of the broader Dutch vs Flemish difference.

Full practice list

The two hardest diphthongs earn deeper treatment: the ui sound and ij vs ei. For the non-gliding vowels and the long–short system behind them, see Dutch vowels.

Frequently asked questions

How many diphthongs does Dutch have?

Three core diphthongs: ij/ei [ɛi], ui [œy] and ou/au [ʌu]. On top of these come the semi-diphthongs aai, ooi, oei, eeuw, ieuw and uw, which are a vowel plus a j or w glide.

Do ou and au sound the same in Dutch?

Yes. ou and au are the same sound, close to the “ow” of English house. koud and saus have the same vowel; the spelling is fixed per word.

Why does Dutch use ou when the old au became oo?

The Germanic diphthong au did become long oo (boom, German Baum). The modern ou mostly came later, from short a or o plus l before d or t, where the l turned into a vowel: oud (old), koud (cold), zout (salt). Other ou/au words come from combinations before w and from loanwords.

Which Dutch diphthong is hardest for English speakers?

ui, because English has no rounded front vowel to start it from. Learners tend to replace it with the English “ow”, which makes huis sound like “house”.

How do you pronounce nieuw and leeuw?

Say the full vowel, then add a clear w-glide: nieuw is roughly “NEE-oow” and leeuw “LAY-oow”, never like English new.