What to wear to a funeral

Funeral dress is one of the few times people worry about clothes for reasons that have nothing to do with clothes. The aim is simple: look like you made an effort, and do not draw attention.
Dark, but not necessarily black
Black is the safe default in much of the UK, the US and Europe, and nobody will ever think it wrong. Charcoal, navy and dark grey are equally acceptable at most services. What matters more than the exact colour is that it is muted and plain.
Some families ask for something different. Requests to wear a colour the person loved, or to avoid black entirely, are increasingly common and are usually written on the notice. Follow what the family asked for. It is their day.
Religion and culture change the rules
This is where general advice runs out. Orthodox and traditional Jewish, Muslim, Hindu and Sikh services all have their own expectations, and white rather than black is the mourning colour in parts of Asia. Covered shoulders, covered legs, and a head covering may be required. If you are attending a service from a tradition you do not know, ask someone who does. Nobody minds being asked.
The practical part
Services often involve standing outside, a walk to a graveside, and several hours before anyone sits down for long. Shoes you can walk on grass in matter more than the sharpest pair you own. Take a coat you would be happy to be photographed in, because you may not take it off.
Autumn and winter funerals
From October onwards the coat is the outfit, because it stays on for the walk, the graveside and the wait outside afterwards. A dark wool coat over whatever is underneath answers most of the question. Gloves and a plain scarf are fine and expected; a hat is fine if it is plain. Boots that can take mud are better than the shoes you would choose for a church floor, and nobody at a winter burial has ever been judged for them.
If the only coat you own is a bright one, a dark scarf and dark trousers or tights under it soften it more than you would think. Borrowing a coat is also normal on this particular day.
Children at a funeral
Children are not expected to be in black. Plain, dark or muted clothes in something they can sit still in are enough, and the school uniform is often the right answer. Avoid anything with characters or slogans on it, and take a layer they can put on outside.
You almost certainly own this already
A dark suit or a plain dark dress, a plain shirt, dark shoes. If you are not sure what you have, this is exactly the sort of thing that is easier to answer by looking at your wardrobe in one place rather than opening three drawers the morning of.
Questions people ask
Do I have to wear black to a funeral?
Not usually. Black is the safe default, but charcoal, navy and dark grey are accepted at most services in the UK, the US and Europe. Follow any request on the notice first; families sometimes ask for colour or for no black at all.
What should I wear to a funeral in winter?
A dark wool coat over dark clothes, plain gloves and scarf, and boots you can stand in on wet grass. The coat will stay on for most of the day, so it matters more than what is underneath.
Can I wear jeans to a funeral?
Only if the family has said the service is informal. Otherwise dark trousers or a dark dress are expected. If jeans are all you have, choose the darkest plain pair, a plain shirt or knit, and proper shoes.