This is fairly mundane task that all of us should do once in a while – making sure that one of the most important site utilities are optimized for optimal user experience (usability) and thus in the end optimal site success; as in MORE money! And the search utility can easily be concluded being among the most important tools by running a basic “Revenue Participation Report” - should you be in doubt whether it is worth doing the task.

Looking at the above report outcome from a random British retailer we instantly see that the search utility participates in £51,416.62 of the overall £120,529.88 revenue for the given period – a whopping 43%. I think we can conclude that for this retailer, where almost half the revenue is involved with site search, it is of the utmost importance that one of the few important design parameters, such as the search query box width, is “calculated” and not just spinelessly handed over to the web-designer as a last minute one man decision.

I find it difficult to persuade myself that a reasonable A/B and or Multivariate testing can be applied with success to this task, given the restrains of different user behaviour when changing this parameter – as in the observable fact that users use longer queries when the search box is wider. And I think that we in general just have to accept that we can get other insights when using qualitative studies.

So; let us have a look at the immediate available data (the number of Searches per Search Query):

Looking at the distribution of this dataset, it looks like a standard long tail (this is a completely different dialogue, but beware of a drooping tail) – However; that is not why we are here today. What we need to do is conclude on: how many characters is needed to accommodate a certain percentage of all search queries in full. I know this is obvious, anyway – now you will at least know how I went about it in EXCEL:

1.
Do a volume export of the upper report (Search Phrase with the number of searches for that phrase)

2.
Import this dataset into EXCEL (in the upper example we have just about 24000 different Search Phrases in the given period)

3.
Add a third column called e.g. “Lenght” – which is the number of characters in that particular search phrase (EXCEL command: LEN() – See picture below, which of course resembles the one from IndexTools’s reporting system)

4.
Then group all those search phrases (rows) with similar length, so that we get a total SUM of searches per search length (Do a quick PivotTable with length being a row – See picture below, which should when summed up still have the same number of total searches, some 24000)

5a.
Then add a column which calculates a “Percent of all Search queries”, so we can start to see how many queries we can accommodate in a search box width of n length. (looking at the picture below - out of the row based data we can see that with as little as 16 Characters we will be able to accommodate full usability on 71% of all our internal search queries).

5b.
Sometimes it is a bit easier to look at this in a scatter chart - for a full view of this see the picture below:

At this time we have all the data needed to conclude on the character width of our internal search box and you might by now ask, why is it that we do not just deploy a search box of e.g. 55 characters width like Google? – But with well researched usability guidelines recommending the internal Search Box being on every page, one simply have to converse space. Therefore in the end, having to make a trade-off, we have to decide how many users we want to fully accommodate by providing them the space needed for their query. The research I have read and agree width concludes that a trade-off (based on the distribution) around 90% of all internal search queries should fit in your search box.

So with that said the conclusion for the site debated above is that:
Internal Search Query box WIDTH should be 23 characters.

Remember; there is no magic number for you to use as this is very much site specific and you simply have to do your own analysis - sorry! :-). I personally recommend redoing this every year.

N.B.
The site debatted have an internal search box width on 35 Characters today and could therefore “save” 12 characters and by that free up space for increased usability. (there is of course other problems with the setup of this one, but that is for another dialogue)