Do we sacrifice consistency and clarity for the sake of convention?

We are familiar with size numbers for shoes, hats, dresses and so on. Ronnie Cohen looks at the convention for screen sizes based on inches and asks if this really makes sense.

I recently came across an article with the title “The new lap of luxury” in the London Life section of the London Evening Standard. This article about laptops appeared on page 35 of the paper and was published on Thursday 13 July 2017. It is an article about Microsoft Surface laptops that aims to challenge Apple’s popular MacBook. The subtitle of the article, at the top of the article, says “Slimmed down, speedy and supercharged – the Microsoft Surface is here to challenge Apple’s computers”.

It followed the convention of giving width, height and depth in centimetres and screen sizes in inches. As the screen size of a folded laptop has a width and height that is almost the width and height of the laptop, one would think that it made more sense to express screen sizes in centimetres for consistency. However, screen sizes are expressed in the UK as so many inches from one corner of the screen to the opposite corner.

One feature of the printed version that does not appear in the online version is the specifications of “The Winning Laps” as the article describes them. Two laptops are shown with their specifications in that part of the printed article, one Microsoft Surface laptop and one MacBook Pro laptop.

The size of the Microsoft Surface laptop is given as 30.8 cm x 22.3 cm x 1.45 cm. The screen size of this laptop is given 13.5 inches.

The size of the MacBook Pro laptop is given as 30.4 cm x 21.2 cm x 1.49 cm. The screen size of this laptop is given as 13.3 inches.

The Evening Standard followed the accepted UK convention of giving laptop sizes in centimetres and screen sizes in inches. Apparently, since the appearance of monitors, laptops, tablets, mobile phones and digital cameras over the past 30 years, few have asked why two incompatible systems are often used for describing the dimensions of the device and its screen size. Size is one physical phenomenon. Using one system would make comparisons easier by letting us just compare the numbers rather than think about conversions from centimetres to inches or inches to centimetres.

Of course, globally there are many countries where inches mean nothing. The screen size in inches is merely a number, its derivation lost in the mists of time, as with sizes of clothing and shoes. But this system of screen sizes, whether inches or centimetres, is consistent around the world thanks to ISO, and for this we should be thankful, even if we have to check the product description or specification to find out how big it really is.

You can read the online version of this article at:

11 thoughts on “Do we sacrifice consistency and clarity for the sake of convention?”

  1. I think we need to introduce the topic of actual measurements versus trade descriptors. The dimensions they are giving you in centimetres are actual measurements, the dimensions in inches are trade descriptors. Trade descriptors don’t have to match the measured value and in most cases they don’t. More often than not, the size is inflated.

    Trade descriptors benefit the manufacturer in that they can change the size and not change the description. Consumer groups in the US a number of years ago found this practice to be deceptive when describing TV screens and monitors and filed a lawsuit in court. The television manufacturers argued that they were trade descriptors and not real measurements. The outcome of the lawsuit forced the manufacturers to make it clearer that the screen sizes were actually trade descriptors. All they did was add the word “class” to the description.

    Presently in the US there is another group of people suing a number DIY stores over the marketing of 2 x 4s. These are supposed to be 2 in x 4 in (50 mm x 100 mm) pieces of wood, but they are smaller, about 40 mm x 90 mm. Some consumers feel they are being deceived even though industry experts insist it is an old practice and everyone in the trade is aware of the short measure.

    Those living outside the US who use metric units daily would never be aware that these odd numbered trade descriptors are somehow connected to measuring units, thus no one in a metric country would ever notice anything odd or deceptive to initiate a complaint. Only in the US and among metric opposers in the UK would one expect someone to notice.

    If they want to use trade descriptors, that would be fine, but at least include the correct metric value for the whole world to compare.


  2. Once I read an ad about a ’24 inch’ screen, but in the accompanied text the screen size was given as 23.6 inches. 0.4 inch is equals 1 cm. This means that the real dimension of the screen is 60 cm. I think that this nonsense is the work of marketeers. So, my screen measures 60 cm. I have seen screen sizes described as 24′ in a shop where I live. Sure, 24 feet, I will need a lorry to get it home. They accept this non-metric size and they do not know the correct symbols for foot and inch. Two more howlers I found in ads or shops: ‘ 24″ inch ‘ and even ‘ 24’ inch ‘!


  3. Han,

    The true size of that 23.6 in screen is exactly 600 mm. 600/25.4 = 23.622 047….. When rounded it becomes 23.6. Another popular size is the 800 mm, hidden under the trade facade of 32 in class, but in fine print 31.5 in which is hidden metric for 800 mm.

    This is what is known as hidden metric.


  4. The problem with screen sizes is not whether they are expressed in inches or centimetres or millimetres, but that these sizes are based on the diagonal measurements of the screens.

    If all screens were the same shape, this would be no problem, but screen dimensions vary, from very nearly square to quite elongated rectangles. Therefore the size of screen does not bear a constant relationship to the area of the screen. Even worse, the area of the screen is the square of the diagonal measurement, and this masks the fact that the larger screen is more expensive to run. (Of course, this only applies if everything else is equal.)

    Here are some examples:

    Double the screen size and it won’t cost you double to run it. It will take four times the power to run the screen.

    An 11 inch screen will take 21% more power to run than a 10 inch screen (not 10% as some might be led to believe).

    A 70cm screen will take about half of the power to run compared with a 100cm screen.

    I think the best thing to do is to ditch the diagonal measurement and use the total area of the screen as the measure.


  5. @Michael Glass:

    At least the EPROM self-description of the screen is always metric in both dimensions, if included. But (a majority of?) computer software which reads this information then converts it into a single imperial DPI which is effectively meaningless to most of the world. To add insult to injury, it will often also round it to a cardinal number so that the value differs significantly from the quoted metric dot pitch which flat-panel displays really are manufactured to ☹.

    I hope never to discover what a muddle such software makes of screens with non-square pixels or unconventional aspect ratios…


  6. In some stores in China, screen sizes are compulsory labeled with diagonal centimetres, although most stores would label the inch value as well. For shoe sizes, the official way is the length of corresponding foot in millimetres, although most people are more familiar with size numbers.

    For us, the “inch” of screen (and pizza), and the “size numbers” of shoes are more like a relative “index” with direct relationships. For example, a 40-inch TV (usually just called 40th screen) is larger than 35-inch or 30-inch ones, but nobody will know by what amount. Similarly, if size 40 shoes are too small, we will try a 40.5 or 41 pair, while nobody care how much larger they are.

    I believe it will be better if screen is measured in L×W by mm or cm, and shoes completely in mm. Then we would not mistake European number by 20C Chinese number (European 30 is Chinese 27, while European 45 is Chinese 47), and have a direct sense for these measurements.


  7. The IT industry is flooded with US influence in it’s measures.

    Just look at the “3.5 inch floppy disk” which was neither 3.5 inch in size OR floppy.

    And to this day we’re still installing equipment in 19 inch racks and measurement of equipment made by the major manufacturers, despite being made in the far east, is still usually inches and product documentation often does not include metric sizes at all.


  8. The significance of this ‘convention vis reality’ came home to me today upon researching for ‘just the right camera’ for an upgrade.
    It all started well with sensor sizes in mm x mm in the title page. But oh my God what a mess it turned into with the ‘convention’ of using inches!!!
    It seems a 1 inch sensor is 12.8 mm x 9.6 mm, a 2/3 inch is 8.8 mm x 6.6 mm and a “tiny 1/3.2-inch image sensor. In real terms this measures just 4.54 x 3.42 mm” (sic). I agree with the sentiment “in real terms”, so why all the nonsense with inches then admitting the real terms are mm?
    I do not know if this is a UK site or USA, I guess UK using USA data? Anyway, the end result is basically I understand very little of a rather complex subject as I just get bogged down in stupid terminology and give up reading it.
    For the avid “lets go back to inches” brigade maybe you would like to post here what the real measurements are in fractions of an inch so “we can all understand it”. Or perhaps not.


  9. Further to my previous post 2017-09-14 at 11:35. The nonsensical descriptors become a little less confusing having learned that the image sensor size in a digital camera is based on the size of a TV video sensor tube. How stupid of me to think it would be based on the size of the ubiquitous camera and photographic film!
    Being conversant as I am with image orthicon and vidicon tubes of yesteryear I can see where they are coming from, (just).
    Far better though that the opportunity be taken to make the descriptors fit the product in question, and everyday life, not a product that 99% of the world population has probably never heard of.


  10. @BrianAC

    It appears from your experience that the information the marketing gurus are presenting to you is not designed to make things clear but to obfuscate. If the justification for this is that the population understands inches and in fractional form, this is obviously a falsehood as who is taught to work in thirds of an inch or fractions with decimal denominators. The average person can only relate to halves and quarters, if that. Few can comprehend eights, and even few yet sixteenths. 1/3.2 if expressed as 10/32 is understood by almost no one. This value is just a hidden approximation for 8 mm.

    8 mm home video system were quite common and most people who grew up with inches understand this size. Is it necessary to describe a sensor as being 4.54 mm x 3.42 mm, when a simple 4.5 mm x 3.4 mm would do? Does that extra precision really make that much of a difference?

    The only way to know for sure why this nonsense is propagated is to question someone in the industry but can we trust their answer?


  11. @Alex Bailey:

    I can’t express how joyful it makes me when I’m allowed to replace 19 imperial inch [computer & networking] ‘rack equipment’ in 2 imperial foots ‘cabinets’ with 500 mm ‘sub-racks’ in 600 mm ‘miscellaneous rack cabinets’ to EN 300‍ ‍119 (slightly different nomenclature) 😂. Those extra ≈60 mm of width suddenly makes USA customary-based PC-like computer parts fit in neatly without loads of wasted space or special power supplies, etc. The 25 mm module height is so much easier to work with and adaptable without silly non-optimal arrangements of components. An ATX motherboard and its front-projecting cables will [just] fit in a 300 mm deep rack or two in a 600 mm deep rack. The cabling channels are standardised. Even forced-air cooling, although less standardised, is typically done more thoughtfully. The rack screws are readily-available M6 metric threaded instead of weird rare USA archaic ‘unified’ (or WHY). The sub-rack dimensions lend themselves to local and in-house fabrication of chassis and thinner metal instead of buying in from afar. Adjacent 150 mm and 300 mm wide cabinets can be used for auxilliary purposes…

    The FaceBook/ Open Compute rack is clearly a more recent attempt to do something similar by a committee which still appears stuck in converted fractional inches, has difficulty with rounded metric and too much NIH exceptionalism to adopt an existing standard. The tool-less assembly and shared switchblade ELV power rails, etc., would be compatible with the ETS, AFAICT.


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