Black tie is the clearest dress code there is, and the one people most often talk themselves out of. Here is exactly what it asks for.
Of all the dress codes on a wedding invitation, black tie is the least ambiguous. It asks for a floor-length gown in an evening fabric, with proper jewelry and a heel.
And yet it is the code that produces the most hesitation, because it sounds like it belongs to somebody else's life. It does not. It is simply an instruction about length and fabric, and it is easier to answer than cocktail, which asks you to make judgements.
Here is the whole thing, including the two neighbouring codes that get confused with it.
Black Tie
Floor length. Evening fabric. That is the instruction.
Evening fabric means satin, velvet, chiffon, lace, crepe with a sheen, or anything with beading or a metallic thread. The surface is what makes a dress read as formal, far more than the shape does. A simple column in satin is properly black tie. An elaborate dress in cotton is not.
Add real jewelry rather than a lot of it. One statement piece, usually an earring, and either a fine chain or nothing at all. A small clutch with no strap, or a strap you can tuck inside.
A heel, though it does not need to be high. A block heel in a matching fabric is entirely correct and much easier to spend six hours in.
Color is open. Black is correct and always has been. Deep jewel colors photograph beautifully in candlelight. Metallics belong here more than anywhere else.
Black Tie Optional
This is the couple telling you a gown is welcome but not required, and it is a genuine choice rather than a polite fiction.
A floor-length gown is right. So is a formal midi in an evening fabric with good jewelry and a heel. Both will look correct in the same photograph, and roughly half the room will choose each.
If you are deciding, let the venue choose for you. A hotel ballroom or a country house at an evening start leans toward the gown. A restaurant or a city venue at six o'clock sits comfortably with a midi.
Formal, and Black Tie Creative
Formal on its own is slightly softer than black tie. Long or a dressy midi, evening fabric, and a little more room for color and print. The instruction is about the register rather than the exact hemline.
Black tie creative is the most enjoyable code on any invitation. It means black tie formality with permission to be interesting: a strong color, an unusual silhouette, a cape, a dramatic sleeve. It is the couple saying they would rather see you than see a room of safe choices.
The thing black tie creative does not mean is a costume, or a reason to dress down. It is a step sideways from black tie, not a step below it.
What Does Not Answer the Code
A cocktail dress at a black tie wedding. It is the commonest error and it is not a disaster, but you will feel it all evening.
A daytime fabric in an evening shape. A floor-length cotton or jersey dress reads as a sundress whatever its length, because the fabric is doing the talking.
White, ivory, cream or champagne, for the usual reason and just as firmly as at any other wedding.
And a shoe you cannot stand in, which is not a dress code error but ends more evenings early than any other choice on this page.
The surface is what makes a dress formal, far more than the shape does. A simple column in satin answers black tie completely.
Choosing a Shape
Once the length and the fabric are settled, the shape is genuinely yours to pick, and the useful question is how you will spend the evening rather than how the dress looks standing still.
A column or a slip falls straight and reads as calm and modern. It is lovely for standing and moving between groups, and it wants smooth underpinnings and a fabric with some weight.
An A-line gown is the most comfortable formal shape there is, particularly for a long seated dinner, and it suits almost every kind of venue.
A fit and flare, fitted to the hip and then released, is the most dramatic on a dance floor and the most forgiving at a table.
An empire line, seamed under the bust, is the easiest to wear for a long evening and the easiest to get right without alterations.
A dress with a sleeve is worth considering for a fall or winter wedding, and it solves the wrap question before it arises. Long sleeve dress styles covers the shapes that work.
Hems, and the One Alteration Worth Paying For
A floor-length dress is hemmed for a specific shoe height, which is the part most people discover too late.
Decide the shoe first. Then have the hem taken up to clear the floor by roughly half an inch in that shoe. It is an inexpensive alteration and it is the difference between a gown that looks made for you and one that catches under your heel every time you turn.
If you would rather not alter anything, an ankle-length or midi in an evening fabric removes the problem entirely, which is one more reason black tie optional is such a friendly code.
Jewelry, Wraps and the Evening Bag
One statement piece. A drop earring is the easiest, because it reads in photographs and never interferes with a neckline. If the dress has a high neck or a detailed shoulder, let the dress be the statement and wear something very fine or nothing.
For your shoulders, a proper wrap in a good fabric rather than a cardigan. Velvet, a heavy silk, or a fine wool in winter. It sits over the back of a chair for most of the evening and earns its place in the twenty minutes outside.
A clutch, small and structured. Phone, lipstick, a bandage, and nothing else.
Three Formal Evenings, Assembled
For the ballroom in winter: a velvet or satin column in a deep color, a block heel, a drop earring, a wrap. Hair off the face.
For the country house in summer: a chiffon or georgette A-line in a soft color, a low heel, a fine chain, and a pashmina for the garden after dinner.
For black tie creative: the color you actually love, in a shape with one bold element, and everything else quiet. If you would like the accessories thought through properly, what to wear with an evening gown covers gloves, wraps and earrings in detail.
Long Dresses for a Formal Evening
Common Questions
What Do You Wear to a Formal Wedding?
A floor-length gown in an evening fabric, with a heel and one good piece of jewelry. Evening fabric means satin, velvet, chiffon, lace or anything with beading, because the surface is what signals formality rather than the shape. If the invitation says black tie optional, a formal midi in the same fabrics is equally correct. Skip white in every shade, and skip a cocktail-length dress in a daytime cloth, which reads as under-dressed however good it is.
Where to Buy Formal Wedding Guest Dresses?
Shop long dress and gown collections rather than occasion dresses generally, since length is the part black tie is strict about. Filter by fabric where you can, because satin, velvet, chiffon and lace all read as evening while cotton and jersey do not, whatever the length. Check the shoulder-to-hem measurement against your height and your chosen shoe, and budget for a hem alteration, which is inexpensive and makes more difference to how a gown looks than almost anything else.
What to Wear to a Formal Wedding as a Guest?
Floor length, evening fabric, one statement piece of jewelry, a heel you can stand in for six hours, and a small clutch. Choose the shape around the evening: a column or slip if you will be standing and moving, an A-line or fit and flare if there is a long seated dinner. Bring a proper wrap rather than a cardigan. Avoid white and anything close to it, and have the hem taken up to clear the floor in the shoes you will actually wear.
The Short Version
Black tie means floor length in an evening fabric, and everything after that is choosing. Pick the shape for how you will spend the night, hem it for the shoe you will wear, add one good earring and a proper wrap, and skip white. Black tie optional gives you a formal midi as an equally right answer. The long-dresses edit is where to start.