Diphthongs: ei, ie, au, eu, äu | German Grammar

A diphthong is a single vowel sound that glides from one position to another inside one syllable — the oy in boy is a diphthong, the ee in see is not. German has just three true diphthongs, and they are spelled in five ways. Learning the sounds takes minutes; the real obstacle is a reading trap that catches nearly every English-speaking beginner: the pair ei versus ie. Get that pair backwards and you will mispronounce some of the most common words in the language — mein, nein, vier, Liebe — every single time. This page gives you the three sounds, the five spellings, and one rule that fixes the ei/ie trap permanently.

The three diphthong sounds

German has exactly three diphthongs, and English has all three too — so the sounds are easy. What's hard is mapping the German spellings onto them.

Sound (IPA)	Like English	German spellings	Examples
[aɪ]	'eye', 'my'	ei, ai	mein, nein, Mai, Kaiser
[aʊ]	'ow', 'cow'	au	Haus, blau, Frau, auch
[ɔʏ]	'oy', 'boy'	eu, äu	neu, heute, Häuser, Bäume

Notice the asymmetry: three sounds, five spellings. ei and ai both give [aɪ]; eu and äu both give [ɔʏ]. And lurking among them is ie, which is not a diphthong at all — it is a long single vowel [iː]. That mismatch is the whole difficulty.

ei (and ai) — like English "eye"

The digraph ei is pronounced [aɪ], exactly like the English word eye or the i in mine. The much rarer ai sounds identical.

mein

[maɪn] — rhymes with English 'mine'; 'my'

nein

[naɪn] — like 'nine'; 'no'

Wein

[vaɪn] — like English 'vine'; 'wine'

Mai

[maɪ] — like English 'my'; the month 'May'

ie — a long "ee", NOT a diphthong

This is the one that catches everyone. ie is not "ee-eh" and it is not "eye". It is a single, long [iː] — the ee in see, the ea in beach. The e is silent; it is just a length mark telling you the i is long.

vier

[fiːɐ̯] — like English 'fear' without the hard r; 'four' — NOT 'fire'

Liebe

[ˈliːbə] — 'LEE-buh'; 'love'

Bier

[biːɐ̯] — like English 'beer'; 'beer'

die

[diː] — 'dee'; the feminine/plural 'the'

The rule that fixes ei vs ie forever

Here is the trick competitors rarely state cleanly. Pronounce the digraph like the English name of its second letter.

ei ends in i, and the English letter i is named "eye" → so ei = "eye" [aɪ].
ie ends in e, and the English letter e is named "ee" → so ie = "ee" [iː].

That's it. Every time you meet ei or ie, glance at the second letter and say its English name. mein → second letter i → "mine". Liebe → second letter e → "LEE-buh".

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Second letter wins. ei → say "I/eye". ie → say "E/ee". This one heuristic resolves thousands of words — weiß ('white', "vice"), wie ('how', "vee"), Zeit ('time', "tsite"), nie ('never', "nee").

The clearest demonstration is the near-minimal pair Wein ('wine') versus Wien ('Vienna'). Same four letters, swapped middle pair, completely different sounds — and a tourist who confuses them is ordering a glass of Austria's capital.

Wein

[vaɪn] — 'wine', with the 'eye' diphthong

Wien

[viːn] — 'Vienna', with a long 'ee'

Ich heiße Maria und ich liebe Wien.

'My name is Maria and I love Vienna.' Notice heiße (ei = 'eye') and liebe/Wien (ie = 'ee') in one breath.

au — like English "ow"

au is [aʊ], the ow in cow or now, or the ou in house. It glides from an open a toward a rounded u.

Haus

[haʊs] — like English 'house'; 'house'

Frau

[fʁaʊ] — rhymes with 'cow'; 'woman / Mrs.'

blau

[blaʊ] — rhymes with English 'cow' (not 'blow'); 'blue'

auch

[aʊx] — 'owch'; 'also/too'

eu and äu — both like English "oy"

Here the spelling forks but the sound does not: eu and äu are both pronounced [ɔʏ], the oy in boy or toy. Why two spellings for one sound? Grammar. äu appears when a word with au changes form — typically a plural or a related word — so the au "umlauts" to äu while keeping the [ɔʏ] sound. eu is the default elsewhere. They are pronounced identically; only the spelling records the word's history.

au form [aʊ]	äu form [ɔʏ]	Meaning
Haus	Häuser	house → houses
Baum	Bäume	tree → trees
Maus	Mäuse	mouse → mice
laufen	läuft	to run → (he) runs

neu

[nɔʏ] — like English 'noy' (boy); 'new'

heute

[ˈhɔʏtə] — 'HOY-tuh'; 'today'

Häuser

[ˈhɔʏzɐ] — same 'oy' as eu; 'houses'

Bäume

[ˈbɔʏmə] — 'BOY-muh'; 'trees'

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When you see äu, do not invent a new sound. It is just eu in disguise — both are "oy". The umlaut on the a is a grammatical flag (this word grew out of an au word), not a pronunciation change.

Two non-diphthongs to keep separate

Watch out for letter pairs that look like they might be diphthongs but are not. ie (covered above) is a long ee. And eu/äu must not be split into "eh-oo" — it is a single glide to "oy". Likewise, when a and u belong to different syllables (as across a compound boundary), they are not the au diphthong: in bauen ('to build') the au is the diphthong [ˈbaʊən], but in a word like Museum the u and e are separate vowels in separate syllables, never a diphthong.

Common Mistakes

❌ mein read as 'meen' [miːn]

Wrong — that treats ei like a long 'ee'. ei = 'eye'.

✅ mein [maɪn]

'My' — rhymes with English 'mine'.

❌ vier read as 'fire' [faɪɐ]

Wrong — that treats ie like the 'eye' diphthong. ie is a long 'ee'.

✅ vier [fiːɐ̯]

'Four' — like English 'fear' (minus the hard r).

❌ Wien (Vienna) pronounced 'Wine' [vaɪn]

Wrong — you've named the drink, not the city. ie = 'ee'.

✅ Wien [viːn]

'Vienna' — long 'ee', like 'veen'.

❌ heute split into 'hay-OO-teh'

Wrong — eu is one gliding sound, not two separate vowels.

✅ heute [ˈhɔʏtə]

'Today' — a single 'oy' glide: 'HOY-tuh'.

❌ Häuser given a brand-new sound for äu

Wrong — äu is not a special vowel; it equals eu.

✅ Häuser [ˈhɔʏzɐ]

'Houses' — identical 'oy' to neu/heute.

Key Takeaways

Three sounds, five spellings: ei/ai = "eye" [aɪ]; au = "ow" [aʊ]; eu/äu = "oy" [ɔʏ].
ie is the impostor: not a diphthong, just a long "ee" [iː].
The master rule for ei vs ie: say the English name of the second letter — ei → "eye", ie → "ee".
Wein (wine) vs Wien (Vienna) is the pair to drill until it's automatic.
äu is just eu with a grammatical umlaut flag; both are "oy". Don't invent a new sound.

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