per vs PM, What's the Difference?

Which to use

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

#339
“per” frequency rank: #2,086
“PM” frequency rank: 2425
confusion score

Side-by-Side Comparison

Feature	per	PM
Definition	For each.	Initialism of post mortem.

Where the eye mixes per and PM

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

3 ch

per

2 ch

Look-alike desk: per vs PM

These two trip readers on the page rather than in the ear: per is /pɜː/ while PM is /ˌpiː ˈɛm/. 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 2425, derived from the frequency rank of both members and their visual similarity.

per is recorded at frequency rank #339, classified as aprep, pronounced /pɜː/. PM is at rank #2,086, tagged as anoun, pronounced /ˌpiː ˈɛm/.

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 2425, this pair ranks #525,016 of 530,003 scored English confusable pairs - a relatively easy-to-tell-apart pair.

Orthographic DNA of per vs PM

Shared letters: p. Private to "per": er. Private to "PM": m.

"per" · 3 letters · shape CVC · "PM" · 2 letters · shape CC

Frequently Asked Questions

Is swapping "per" for "PM" ever safe?

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

Frequency check: "per" vs "PM" - which ranks higher?

"per" is the more common of the two: it sits at frequency rank #339 in our English list, against #2,086 for "PM". The two are close in frequency, so neither is a safe default; check the meaning rather than guessing.

After this comparison

Visual near-miss handled. Browse the word pages or a neighbour when the next look-alike shows up.

Full dictionary entry for "per" with definition, IPA, and generated misspellings. Word entry
Full dictionary entry for "PM" - compare definitions side by side with the headword page. Word entry
This pair ranks #525,016 of 530,003 scored English confusable pairs in this corpus vintage. Corpus statistics
"per" and "PM" also get mixed up with nearby pairs, the highest-scored neighbour is "PM vs PPA". Nearby pair

Confusion rank #525,016 of 530,003 scored English pairs, corpus vintage 2026-09-03, not spelling advice.