ZIP input or ZIP+4

Question

I see that some site forms use the ZIP+4 method of an input, while others just use ZIP. How often do people actually know their ZIP+4? Also, what companies really benefit from this or require it? Just debating the best route for a typical ZIP input.

Answer 1

The best route is to allow both. If someone knows it and wants to enter it, it doesn't hurt you at all.

Zip+4 makes it easier to have things sorted when shipped out. For some companies that are shipping lots of items, this can save on shipping costs if they agree to presort the things they are shipping. This typically only really happens with things like magazines or other bulk mailers (ads, catalogs, bills, etc.).

Answer 2

I did a quick search on how to find your Zip+4 code and there seems to be no definite way to find it (and the USPS page for it is broken). Most people seem to revert to looking at their mail to determine it (As per Yahoo answers). However with regards to if the Zip+4 code is really needed, I think this excerpt from Wikipedia explains it best :

In 1983, the U.S. Postal Service began using an expanded ZIP code system that it called ZIP+4, often called "plus-four codes", "add-on codes", or "add ons". A ZIP+4 code uses the basic five-digit code plus four additional digits to identify a geographic segment within the five-digit delivery area, such as a city block, a group of apartments, an individual high-volume receiver of mail or any other unit that could use an extra identifier to aid in efficient mail sorting and delivery. But initial attempts to promote universal use of the new format met with public resistance, and today the plus-four code is not required. In general, mail is read by a multiline optical character reader (MLOCR) that almost instantly determines the correct ZIP+4 code from the address

Quoting from this discussion on a forum (Note: the responses are not supported by solid facts)

The zip code gets it to the right post office. With the zip+4, it can be sorted to which letter carrier will deliver it. It can even be sorted into the right order.

If your handwriting is good, the zip+4 won't get your mail there any faster. They have software capable of reading the address instead. But if your handwriting sucks, it has to be shunted off into a pile for an actual human being to read, and they may take a while to get around to it.

When zip codes were first introduced, a lot more stuff was done by hand, and the zip code and zip+4 made a bigger difference. People can sort numbers very quickly, and looking up actual street addresses and figuring out the carrier route was a lot of work.

These days, it's unlikely to take more than a day or two longer without the zip+4. In fact, it's usually the same, with our without the zip+4; the software has gotten amazingly good at reading the addresses without human help.

So considering that most of the web based inputs would printed if used for shipping or delivery notifications, you would not need a Zip+4 code as a normal zip code would suffice