BTU vs but, What's the Difference?

Which to use

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

#45,246
“BTU” frequency rank: #25
“but” frequency rank: 45271
confusion score

Side-by-Side Comparison

Feature	BTU	but
Definition	Initialism of British thermal unit.	Apart from, except (for), excluding.

Where the eye mixes BTU and but

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

3 ch

BTU

3 ch

but

Look-alike desk: BTU vs but

These two trip readers on the page rather than in the ear: BTU is /biː.tiː.juː/ while but is /ˈbʌt/. Spoken aloud the problem disappears. In writing it persists, because they differ only by swapping two adjacent letters (tu ↔ ut) - a transposition the eye reads straight past, and the parts of speech differ too (noun vs preposition), which is usually the fastest check. Our composite confusion score for this pair is 45271, derived from the frequency rank of both members and their visual similarity.

BTU is recorded at frequency rank #45,246, classified as anoun, pronounced /biː.tiː.juː/. but is at rank #25, tagged as aprep, pronounced /ˈbʌt/.

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 45271, this pair ranks #222,807 of 530,003 scored English confusable pairs - roughly mid-pack for confusability.

Orthographic DNA of BTU vs but

Shared letters: btu. Private to "BTU": -. Private to "but": -.

"BTU" · 3 letters · shape CCV · "but" · 3 letters · shape CVC

Frequently Asked Questions

Is swapping "BTU" for "but" ever safe?

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

Frequency check: "BTU" vs "but" - which ranks higher?

"but" is the more common of the two: it sits at frequency rank #25 in our English list, against #45,246 for "BTU". That is a wide gap, so in ordinary text the rarer spelling is the one worth double-checking.

After this comparison

Eye-level mix-up between "BTU" and "but" is sorted above. Next: full entries or other pairs that share a letter shape.

Full dictionary entry for "BTU" with definition, IPA, and generated misspellings. Word entry
Full dictionary entry for "but" - compare definitions side by side with the headword page. Word entry
This pair ranks #222,807 of 530,003 scored English confusable pairs in this corpus vintage. Corpus statistics
"BTU" and "but" also get mixed up with nearby pairs, the highest-scored neighbour is "BFS vs BTU". Nearby pair

Confusion rank #222,807 of 530,003 scored English pairs, corpus vintage 2026-09-03, not spelling advice.