Pick the words off your invitation and see what they mean for a woman — the length, the shoes, what not to wear, and where the code sits between its neighbours. Add the event, the hour, the venue and the season and the answer adjusts, saying which part is a source’s and which is ours.
Cocktail attire
Knee-length or midiWhere it sits on the scale.
What the guides say
What not to wear
For your event
Definitions quoted from Debrett’s, Wikipedia’s Western dress codes and semi-formal wear, Joy and Kennedy Blue. Checked 2026-09-20 and 2026-09-22. Anything marked “ours” is our own practical note, not a rule a guide prints.
Quick answer: the length is the code. White tie is floor-length, no exceptions. Black tie is a gown, or a rich knee-length or midi. Black tie optional and formal let you choose either. Cocktail is knee-length or midi and explicitly not floor-length. Dressy casual and below is a sundress or polished separates. And “semi-formal” is the one to be careful with: traditionally it means black tie, in modern American wedding use it sits below cocktail.
How to use it
Pick the words printed on your invitation — or tap a rung on the scale — and you get the length, the shoes, what the guides actually say, and what not to wear. Then add what you know: the event, the hour it starts, the venue and the season. Each line tells you whether it comes from a published guide or from us; nothing here pretends to be a rule that nobody wrote down.
The one that catches everybody: “semi-formal”
Traditionally semi-formal IS black tie: “black tie for evening wear and black lounge suit for day wear, corresponded by either a pant suit or an evening gown for women.” But “in more colloquial, modern formulations, semi-formal has been defined closer to what is traditionally considered ‘informal wear’” — which is where US wedding guides put it, a step below cocktail: “a midi or knee-length dress in a polished fabric”. If the invitation gives you nothing else to go on, look at the venue and the hour: a ballroom at 7pm is the old meaning, a restaurant at 4pm the new one. Sources: Wikipedia: Semi-formal wear and Joy.
The only thing the hour really decides
The oldest rule in the book, and the only one the hour really decides: “Whether one would choose to wear morning or evening semi-formal has traditionally been defined by whether the event will commence before or after 6:00 p.m.” (Wikipedia: Semi-formal wear) Before six, read your code its daytime way — lighter colours, lighter fabrics. After six, read it its evening way.
All thirteen codes, most formal first
| Code | Length | Shoes | What not to wear |
|---|---|---|---|
| 1. White tie | Floor-length, always | Heels you can stand in all evening; this code comes with a long dinner. | Anything short — this is the one code with no shorter option; Daytime fabrics: cotton, linen, jersey |
| 2. Black tie | Floor-length is traditional; a rich knee-length or midi is accepted | Evening heels or elegant flats; a small clutch, not a day bag. | A regular dark suit — “wearing a regular dark suit to a black tie event” is Joy’s one named mistake; Daytime prints and casual fabrics |
| 3. Black tie optional | Your choice: floor-length, or a dressy midi or knee-length | Heels, or dressy flats in a fabric that reads evening. | Treating “optional” as “casual” — it is one notch down from black tie, not three |
| 4. Formal | Floor-length or a polished midi | Heels or polished flats. | Underdressing: of all the codes, this is the one guides warn about most |
| 5. Semi-formal | Midi or knee-length in modern use; floor-length in the traditional sense | Heels or smart flats. | Assuming it means casual — in its original sense this code IS black tie |
| 6. Cocktail attire | Knee-length or midi — not floor-length | Heels; a clutch rather than a shoulder bag. | “Wearing a floor-length gown to a cocktail wedding” — Joy names this one outright |
| 7. Festive attire | Cocktail length, with more colour | Whatever you would wear to cocktail. | Costume: festive means colour and sparkle, not a theme |
| 8. Garden party | Midi or tea-length | Block heels, wedges or smart flats. | Stiletto heels on grass — they sink; a block heel or a wedge does not; Anything strapless if the day may turn cold |
| 9. Beach formal | Maxi or airy midi | Flat sandals, or heels you can take off. | “Wearing all white to a beach wedding”; Heels that sink into sand |
| 10. Lounge suit | Knee or midi; a suit is equally correct | Mid heels. | Reading “informal” as casual — on a British invitation it means a suit |
| 11. Dressy casual | Anything from knee to maxi, as long as it is polished | Flats, low heels or smart sandals. | Jeans, unless the invitation says so |
| 12. Smart casual | Your call | Flats or low heels by day, higher in the evening. | Denim — Debrett’s names it, “even designer denim” |
| 13. Casual | Anything comfortable that still looks considered | Flats, sandals or clean trainers if the invitation is truly casual. | “Distressed denim, flip-flops, athletic wear, and graphic tees” |
Cocktail versus semi-formal versus black tie optional
These three sit next to each other and get muddled constantly. Cocktail is the clearest: knee-length or midi, and Joy names the mistake outright — “wearing a floor-length gown to a cocktail wedding”. Black tie optional is a step dressier: “a floor-length gown, a dressy cocktail dress, or an elegant midi dress” — the gown is genuinely on the table. Semi-formal is the ambiguous one above. If you have nothing else to go on, a polished midi is correct at all three.
Three worked examples
“Cocktail attire”, a hotel ballroom, 7pm, December. Knee-length or midi, not a gown. After six, so the evening reading: a richer fabric, a darker colour, an evening bag. Winter adds velvet, satin or wool crepe — and plan the coat, because the photographs happen outside.
“Black tie optional”, a beach, 4pm, July. Your choice of a gown or a dressy midi, but the venue decides more than the code does: lightweight fabric, a hem that will not drag, and flat sandals or heels you can take off. Never all white at a beach wedding.
“Semi-formal”, a church, 2pm, spring. Before six and in a church: the modern reading — a midi or knee-length in a polished fabric — with the shoulders covered, and a layer, because spring evenings turn cold the moment the sun goes.
Common mistakes
- Reading “optional” as “not really”. Black tie optional is one notch below black tie, not three.
- Wearing a gown to a cocktail event. The one mistake the wedding guides name by itself.
- Assuming semi-formal is casual. In its original sense it is black tie.
- Reading a British “informal” as casual. On a UK invitation, informal means a lounge suit — a skirt or trouser suit, or a dress and jacket.
- White at a wedding. Never white, ivory or cream at a wedding unless the couple asked for it.
- Stilettos on grass. They sink. A block heel or a wedge does not — our note, not a rule anybody prints.
More on Needle Style
Cocktail dresses that work for weddings and work parties, black tie outfits that follow the rules, wedding guest dress ideas, what to wear to a formal gala, what to wear to an outdoor wedding and what to wear to a bridal shower.
Definitions quoted from Debrett’s and Wikipedia: Western dress codes (2026-09-20), Wikipedia: Semi-formal wear, Joy and Kennedy Blue (2026-09-22).
FAQ
What is cocktail attire for a woman?
A knee-length or midi dress that still feels upscale — or a dressy jumpsuit or chic separates — with elegant heels and a clutch. The one thing to avoid is a floor-length gown, which is a step too formal for the code.
What is the difference between cocktail and semi-formal?
In modern American wedding use, semi-formal sits just below cocktail: a midi or knee-length dress in a polished fabric, or dressy separates. Traditionally, though, semi-formal is black tie — so read the venue and the hour. A polished midi is safe at either reading.
What does black tie optional mean?
You may wear a floor-length gown, a dressy cocktail dress or an elegant midi. It is one notch below black tie — the host is saying a gown is welcome but not required, not that the evening is casual.
What is the difference between formal and semi-formal?
Formal expects a floor-length or polished midi dress and warns you not to underdress. Semi-formal, in its modern sense, allows a knee-length dress and dressy separates. In its traditional sense semi-formal is the dressier of the two, which is why the word causes so much trouble.
What should I wear to a black tie wedding?
A floor-length evening gown is the traditional answer, and an elegant knee-length or midi cocktail dress in a rich fabric is widely accepted — Debrett’s calls the knee-length cocktail dress “the most popular choice”. Evening heels, a clutch, and no daytime prints.
What does festive attire mean?
Cocktail length with permission to be bolder — colour, sparkle, a statement shoe. The wedding guides list it as a code but give almost no garment rules for it, which tells you it is about mood rather than hemline. It is not a costume.
What do I wear if the invitation says nothing?
Start at cocktail, the middle of the scale, and adjust by venue and hour: a ballroom at 7pm pulls you up a notch, someone’s garden at 3pm pulls you down one. Overdressing slightly is the error people forgive.
Can I wear black to a wedding?
Yes — black is standard for black tie and cocktail, and none of the guides here bars it. The colour to avoid is white, ivory or cream, unless the couple asked for it.