Colour or color? Organise or organize? Neither is wrong. They are the British and American spelling of the same word, and both are correct English. What looks careless is a text that uses both: a favourite in the first paragraph and a favorite in the third tells the reader that nobody looked closely.
This guide covers the spelling patterns that differ most often, the words that trip people up, and a simple way to keep one variant from the first line to the last.
First, choose your spelling variant
The right choice usually depends on who reads the text, not where you live:
- Writing for a company or a publication? Use its house style. Many organizations name a variant, and some name a dictionary too.
- Writing for readers in one country? Use theirs: American spelling for the United States, British for the United Kingdom and Ireland.
- Writing for an international audience? Either works. Pick one and stay with it.
Australian, New Zealand and South African English mostly follow British spelling. Canadian English mixes the two: it writes colour and centre like British English, but often organize and realize like American English.
The main British vs American spelling differences
| Pattern | British | American |
|---|---|---|
| -our / -or | colour, favour, honour, labour | color, favor, honor, labor |
| -ise / -ize | organise, realise, recognise | organize, realize, recognize |
| -yse / -yze | analyse, paralyse | analyze, paralyze |
| -re / -er | centre, theatre, metre, fibre | center, theater, meter, fiber |
| -ll- / -l- | travelled, cancelling, modelling | traveled, canceling, modeling |
| -l / -ll | fulfil, enrol, skilful, instalment | fulfill, enroll, skillful, installment |
| -ence / -ense | defence, offence, licence (noun) | defense, offense, license |
| -ogue / -og | catalogue, analogue | catalog, analog |
| ae, oe / e | paediatric, manoeuvre, oestrogen | pediatric, maneuver, estrogen |
-our vs -or spellings
The best known difference, and it carries through to related words: colourful and colorful, favourite and favorite. Not every -our word changes, though. Glamour keeps its u in American English too, and glamorous drops it in both.
-ise vs -ize spellings
This is the one that confuses people most, because British English accepts both. Organise is the more common British form, but organize is not an Americanism: some British publishers and dictionaries prefer it. American English uses -ize.
A group of words ends in -ise in every variant, because the ending is part of the word rather than a suffix: advertise, advise, compromise, exercise, revise, supervise, surprise and televise. Writing advertize is wrong on both sides of the Atlantic.
-re vs -er spellings
Centre, theatre and litre in British English, center, theater and liter in American English. One trap: a measuring device is a meter everywhere, so a British text can rightly have a gas meter that is a few metres from the door.
Double L vs single L spelling
British English usually doubles a final l before an ending that starts with a vowel, whatever the stress: travel, travelled, traveller. American English usually doubles it only when the stress falls on the last syllable, so traveled but controlled. Oddly, a handful of words go the other way: British fulfil and enrol, American fulfill and enroll.
Practice vs practise, licence vs license
British English spells the noun with a c and the verb with an s: you practise the piano every day because practice pays off, and a licensed driver holds a licence. American English uses practice for both, and license for both. A spell checker set to British English can catch the noun and verb mix-up only where the sentence makes the role clear, so these deserve a look of your own.
Key single-word spelling differences
- grey (British) and gray (American)
- tyre and tire, kerb and curb, cheque and check
- programme and program, though British English writes program for software too
- aluminium and aluminum, sceptical and skeptical, plough and plow
It is not only spelling differences
A consistent text also keeps the conventions that go with its variant:
- Dates. 10/11/2026 is the 10th of November in Britain and October 11th in the United States. In a text for both, write the month as a word.
- Quotation marks. American style uses double quotation marks and puts a full stop or comma inside them. British style often uses single quotation marks and puts the punctuation inside only when it belongs to the quotation.
- Collective nouns. British writers often say the team are, American writers almost always the team is. Both are fine; switching within a text is not.
How to keep one spelling variant throughout
- Tell the checker which variant you mean. In the Online Spell Checker, choose English (US) or English (UK), or the Australian, Canadian, New Zealand or South African variant. Do not rely on detection for this: when the checker detects English by itself, it checks it as American English, so every British spelling would be marked.
- Let the marks find the strays. With the right variant chosen, a spelling from the other one is flagged as a mistake. That turns a slow hunt for stray spellings into a list.
- Decide on -ise or -ize yourself. Because British English accepts both, a British check may let both through. Choose one, then search the text for the other ending.
- Mind text you paste in. Quotations, emails and passages written by colleagues bring their own spelling. Quotations keep theirs; everything else should follow yours.
- Write it down. For a long project or a team, a short list of decisions (the variant, -ise or -ize, how dates and quotation marks look) saves the same discussion every time.
Spelling is one item on a longer list. For the rest, see A proofreading checklist before you hit send.