Mixing UK and US English in the same document is one of the most common reasons a piece of writing feels 'off' — even when there's no single obvious error. A reader can't always articulate what's wrong; they just feel that the text hasn't been proofread properly. Here's a quick reference, plus how to stay consistent without thinking about it.
This is what an unproofread mixed-locale paragraph looks like — a real problem for anyone writing for both audiences:
Our organization organisation has decided to prioritise customer behavior behaviour analysis this quarter.
The sentence isn't wrong — it's inconsistent. UK 'prioritise' next to US 'organization' and 'behavior' reads as if two people wrote it. Pick one locale and stick to it.
-our vs -or
- colour / color
- favour / favor
- honour / honor
- labour / labor
- neighbour / neighbor
- behaviour / behavior
-ise vs -ize
- organise / organize
- realise / realize
- recognise / recognize
- apologise / apologize
- prioritise / prioritize
Note: Oxford UK style actually accepts -ize; most UK publications use -ise. Pick one and stick with it. If you're writing for a specific publication, check their style guide first — some UK newspapers are strict about -ise, others don't care.
-re vs -er
- centre / center
- theatre / theater
- metre / meter (the unit — 'meter' is the device in both)
- litre / liter
- fibre / fiber
Doubled consonants
- travelling / traveling
- travelled / traveled
- cancelled / canceled
- modelling / modeling
- labelled / labeled
-ce vs -se
- defence / defense
- offence / offense
- licence (noun) / license (both noun and verb in US)
- practice (noun) / practise (verb) — US uses practice for both
Individual words
- grey / gray
- aeroplane / airplane
- aluminium / aluminum
- programme (TV) / program (both in US)
- cheque / check
Vocabulary that isn't just spelling
Spelling is only half of it. UK and US English disagree on entire words too — 'pavement' vs 'sidewalk', 'lorry' vs 'truck', 'holiday' vs 'vacation', 'flat' vs 'apartment'. A proofreader won't always flag these because they're both correct; it's your job to pick the audience and match.
On my holiday I took the lift to the ground floor, walked along the pavement to the car park, and posted a letter at the post office.
On my vacation I took the elevator to the first floor, walked along the sidewalk to the parking lot, and mailed a letter at the post office.
The dates and punctuation trap
- Dates: UK is 8 July 2026; US is July 8, 2026 (and often 7/8/26, which reads as 7 August in the UK).
- Quotes: UK often uses 'single' quotes for speech; US uses "double" throughout.
- Punctuation inside quotes: US puts commas and full stops inside the quotes; UK usually keeps them outside if they aren't part of the quoted material.
- Serial (Oxford) comma: standard in US academic writing; optional in UK writing.
How to stay consistent
Pick UK or US in your writing tool's settings before you start — not after. In Verbao, choose your locale in settings and the proofreader will flag any word that drifts to the other variant. Set it once at the top of a new document and you'll never mix locales by accident again.
The best test at the end of a piece: search your document for the six words most likely to give you away — 'colour', 'organise', 'centre', 'defence', 'travelling', 'grey' — and make sure they all match your chosen locale. Two minutes, and it makes the difference between 'clearly proofread' and 'clearly a first draft'.