A packing list is a sum, not a wish list.

How many of each thing: the actual arithmetic

One set of clothes covers as many days as you go without washing. That is the whole rule, and everything else follows from it:

• Underwear and socks: the cycle plus one. The spare is for the day something gets soaked, not for good luck.
• Tops: half the cycle plus one — unless it is hot and muggy, and then it is one a day, because they will not dry overnight and you will not want to wear them twice.
• Trousers and skirts: a third of the cycle, or a quarter in cold months, when they are worn under layers and stay clean longer.
• Past twelve days, the amounts stop growing. Nobody packs thirty sets of underwear: at that length washing once on the way is not an option, it is the plan. Saying so is more useful than printing an absurd number.

What we measure, and what we will not tell you

The monthly figures come from a real weather station — named on every page, with its distance from the city and the years behind each average. Twenty years of daily records, from the NOAA Global Summary of the Day. Not a forecast: a forecast for your dates does not exist yet when you are packing three weeks out, and a normal month is what you can actually plan for.

Three destinations in the catalogue have no station close enough with a long enough record. Their pages say so and drop the table, rather than filling the gap with something plausible.

• We publish: monthly averages, the day-to-night gap, rainy days, the plug and voltage of the country, and dress codes where the site itself publishes one.
• We do not publish: forecasts, airline cabin sizes or baggage allowances, prices, or a dress code that is merely customary.

Cabin bag only

Cabin mode does not shrink the essentials — that is how people end up short of clean clothes. It drops the optional extras and suggests washing instead, because washing once is what actually makes a week fit into a small bag.

What it will not do is tell you the dimensions your airline allows or what its liquid rules are today. Those change, they differ by carrier, and a page that guesses them costs you a bag at the gate.

Set it once, then adjust it trip by trip

A page you read is not a list you carry. In the Joru app the same list lives on your phone: you set up your default packing list —what you always take, in the amounts you always take— and every trip after that starts from it instead of from a blank page.

Then each trip edits it, because four days in October and two weeks in July are not the same suitcase. Change the amounts, drop what you do not need, add what only this trip needs, and tick it off while you pack. The destination pages here are the starting point; the app is where it becomes yours.

• Your default list, set once. No more building a packing list from zero.
• Edited per trip. The changes belong to that trip and leave your default alone.
• On the device. The days, the places and the list in one app, and nothing about your trip leaves your phone.