sein vs seis, What's the Difference?

Which to use

“sein” is a verb and “seis” is a num - they look or sound alike but fill different roles in a sentence.

#45,601
“sein” frequency rank: #596
“seis” frequency rank: 46197
confusion score

Side-by-Side Comparison

Feature	sein	seis
Definition	Ser, estar.	Cinco y uno.

Where the spellings diverge

Shared letters are muted; the letters that actually set sein and seis apart are highlighted. They share 3 letters in sequence, which is exactly why the eye skips the difference.

4 ch

sein

4 ch

seis

Spelling & Dictionary Insight

These two trip readers on the page rather than in the ear: sein is [ˈzaɪ̯n] while seis is [ˈsejs]. Spoken aloud the problem disappears. In writing it persists, because they differ by a single letter - n in “sein” becomes s in “seis”, and the parts of speech differ too (verb vs num), which is usually the fastest check. Our composite confusion score for this pair is 46197, derived from the frequency rank of both members and their visual similarity.

sein is recorded at frequency rank #45,601, classified as averb, pronounced [ˈzaɪ̯n]. seis is at rank #596, tagged as anum, pronounced [ˈsejs].

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 46197, this pair ranks #127,121 of 323,831 scored Spanish confusable pairs - roughly mid-pack for confusability.

Orthographic DNA of sein vs seis

Shared letters: eis. Private to "sein": n. Private to "seis": -.

"sein" · 4 letters · shape CVVC · "seis" · 4 letters · shape CVVC

Known mistypes of this pair

sein ← esin · seinn · seni · ssein
seis ← ceis · esis · seiss · sesi · sies · sseis

Frequency comparison

sein#45,601

seis#596

Source: FrequencyWords open word-frequency list

Frequently Asked Questions

Can "sein" and "seis" be used interchangeably?

No - they are not even the same part of speech. "sein" is a verb and "seis" a num, so a sentence built for one is usually ungrammatical with the other.

Which is more common, "sein" or "seis"?

"seis" is the more common of the two: it sits at frequency rank #596 in our Spanish list, against #45,601 for "sein". That is a wide gap, so in ordinary text the rarer spelling is the one worth double-checking.

Remembering sein vs seis

The fastest way to pick the right one every time.

Check the role first: if you need a verb, it's “sein”; for a num, it's “seis”.
See each word in full, definition, IPA, etymology and its other confusables. Full “sein” entry
Browse more pairs most likely to be confused. Most confusable