British and American spelling differences are best understood as two overlapping standards, not as a list in which one side is correct and the other mistaken. The systems share most spellings, differ predictably in some families and contain exceptions shaped by individual word histories.
British and American academic English are largely the same language, but their spelling conventions differ in visible and sometimes inconsistent ways. Neither system is inherently more correct. The practical aim is to use the variety required by your institution, publisher or audience and apply it consistently.
-our and -or
Many British spellings retain -our where American spelling uses -or:
- colour / color
- behaviour / behavior
- labour / labor
- favour / favor
- neighbour / neighbor
Not every word follows the pattern. Author, doctor and error are spelled the same in both varieties.
-re and -er
Some British words end in -re where American English uses -er:
- centre / center
- metre / meter
- theatre / theater
- litre / liter
In British English, meter remains the spelling for a measuring instrument, such as a parking meter, while metre is the unit of length.
-ise and -ize
American English usually prefers -ize: organize, recognize, standardize. British English commonly uses -ise: organise, recognise, standardise.
However, -ize is also an established British convention, notably in Oxford style. It is therefore inaccurate to treat every British -ize spelling as an Americanism.
Some verbs must use -ise in both systems because the ending is not the same suffix. Examples include advertise, advise, comprise, revise and surprise.
-yse and -yze
Here the division is clearer. British English normally uses -yse, while American English uses -yze:
- analyse / analyze
- paralyse / paralyze
- catalyse / catalyze
Oxford’s preference for -ize does not normally extend to these -yse verbs.
Doubled consonants
British English often doubles a final l before a suffix even when the last syllable is unstressed:
- travelling / traveling
- labelled / labeled
- modelling / modeling
- counsellor / counselor
Both varieties double the consonant in words where stress and spelling rules require it, such as beginning.
Licence and license
In British English, licence is normally the noun and license the verb:
- She holds a driving licence.
- The authority will license the operator.
American English generally uses license for both noun and verb.
Practice and practise
British English usually distinguishes the noun practice from the verb practise:
- Regular practice improves performance.
- Students should practise the method.
American English normally uses practice for both.
Defence, offence and pretence
British English uses -ce in defence, offence and pretence; American English uses defense, offense and pretense. Related adjectives use s in both varieties: defensive, offensive.
Programme and program
British English normally uses programme for a planned series of activities, a television programme or a programme of study. Program is standard for computer code. American English generally uses program in all these senses.
Other frequent differences
- catalogue / catalog
- dialogue / dialog, although dialog is common in computing
- grey / gray
- jewellery / jewelry
- cheque / check, for the banking noun
- fulfil / fulfill
- enrolment / enrollment
- paediatric / pediatric
- haematology / hematology
Do not alter quotations, titles or official names
When quoting a source, preserve its original spelling unless your style guide explicitly allows silent changes. Keep the official spelling of organisations, publications, software commands and proper names. A British paper may still discuss the World Health Organization because that is its official name.
Choose a style and run a consistency check
Set the document language in your word processor, but do not rely on automatic checking alone. Search for common pairs such as organisation/organization, analyse/analyze, behaviour/behavior and licence/license. Check references and quotations separately.
Consistency is more important than performing Britishness or Americanness word by word. Follow the required house style, preserve intentional exceptions, and make the spelling system invisible to the reader.
Consistency beats caricature
British English can legitimately use many -ize spellings, especially in Oxford style, while some words always require -ise. American English also preserves spellings that look “British” in particular words. Choose the required style guide, then check families of spellings consistently rather than converting mechanically.