au vs auf, What's the Difference?

Which to use

“au” is an intj and “auf” is a preposition - they look or sound alike but fill different roles in a sentence.

#7,821
“au” frequency rank: #35,364
“auf” frequency rank: 43185
confusion score

Side-by-Side Comparison

Feature	au	auf
Definition	Indica dolor.	Arriba de, sobre, en.

Where the eye mixes au and auf

Muted = shared; highlighted = the visual trap. They share 2 letters in sequence.

2 ch

3 ch

auf

Why the eye confuses au with auf

These two trip readers on the page rather than in the ear: au is [ˈaw] while auf is [aʊ̯f]. Spoken aloud the problem disappears. In writing it persists, because they differ by 1 extra letter(s) - “au” sits inside “auf”, and the parts of speech differ too (intj vs preposition), which is usually the fastest check. Our composite confusion score for this pair is 43185, derived from the frequency rank of both members and their visual similarity.

au is recorded at frequency rank #7,821, classified as anintj, pronounced [ˈaw]. auf is at rank #35,364, tagged as aprep, pronounced [aʊ̯f].

Glosses for this pair are partially populated in our dataset, but the full side-by-side definitions above should still guide you to the right choice.

With a confusion score of 43185, this pair ranks #144,085 of 323,831 scored Spanish confusable pairs - roughly mid-pack for confusability.

Orthographic DNA of au vs auf

Shared letters: au. Private to "au": -. Private to "auf": f.

"au" · 2 letters · shape VV · "auf" · 3 letters · shape VVC

Frequently Asked Questions

Can "au" and "auf" be used interchangeably?

No - they are not even the same part of speech. "au" is an intj and "auf" a preposition, so a sentence built for one is usually ungrammatical with the other.

In ordinary Spanish text, does "au" or "auf" show up more?

"au" is the more common of the two: it sits at frequency rank #7,821 in our Spanish list, against #35,364 for "auf". The two are close in frequency, so neither is a safe default; check the meaning rather than guessing.

What to do next

Pronunciation already separates them, if the page still looks alike, the dictionary links below settle it.

Full dictionary entry for "au" with definition, IPA, and generated misspellings. Word entry
Full dictionary entry for "auf" - compare definitions side by side with the headword page. Word entry
This pair ranks #144,085 of 323,831 scored Spanish confusable pairs in this corpus vintage. Corpus statistics
"au" and "auf" also get mixed up with nearby pairs, the highest-scored neighbour is "atl vs auf". Nearby pair

Confusion rank #144,085 of 323,831 scored Spanish pairs, corpus vintage 2026-09-03, not spelling advice.