per vs pi, What's the Difference?

Which to use

“per” is a preposition and “pi” is a noun - they look or sound alike but fill different roles in a sentence.

#339
“per” frequency rank: #8,073
“pi” frequency rank: 8412
confusion score

Side-by-Side Comparison

Feature	per	pi
Definition	For each.	The sixteenth letter of the Classical and Modern Greek alphabets and the seventeenth in Old Greek.

Where the eye mixes per and pi

Muted = shared; highlighted = the visual trap. They share 1 letter in sequence.

3 ch

per

2 ch

Spelling & Dictionary Insight

These two trip readers on the page rather than in the ear: per is /pɜː/ while pi is /paɪ/. Spoken aloud the problem disappears. In writing it persists, because they differ by 1 letter(s) in length, and the parts of speech differ too (preposition vs noun), which is usually the fastest check. Our composite confusion score for this pair is 8412, derived from the frequency rank of both members and their visual similarity.

per is recorded at frequency rank #339, classified as aprep, pronounced /pɜː/. pi is at rank #8,073, tagged as anoun, pronounced /paɪ/.

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 8412, this pair ranks #502,624 of 530,003 scored English confusable pairs - a relatively easy-to-tell-apart pair.

Orthographic DNA of per vs pi

Shared letters: p. Private to "per": er. Private to "pi": i.

"per" · 3 letters · shape CVC · "pi" · 2 letters · shape CV

Frequently Asked Questions

Can "per" and "pi" be used interchangeably?

No - they are not even the same part of speech. "per" is a preposition and "pi" a noun, so a sentence built for one is usually ungrammatical with the other.

Which is more common, "per" or "pi"?

"per" is the more common of the two: it sits at frequency rank #339 in our English list, against #8,073 for "pi". That is a wide gap, so in ordinary text the rarer spelling is the one worth double-checking.

What to do next

You've compared "per" and "pi". Here's where to go from here.

Full dictionary entry for "per" with definition, IPA, and generated misspellings. Word entry
Full dictionary entry for "pi" - compare definitions side by side with the headword page. Word entry
This pair ranks #502,624 of 530,003 scored English confusable pairs in this corpus vintage. Corpus statistics
"per" and "pi" also get mixed up with nearby pairs, the highest-scored neighbour is "pi vs PPA". Nearby pair

PlainSpell is a reference corpus, not spelling advice. Verify unusual forms in context.