15 July 2012

USA vs UK/European Ring Sizes

I'm often see people questioning the ring sizes of different Filofax personal organisers for sale on Filofax USA.  I sometimes end up 'throwing my toys out of my pram' in frustration that someone somewhere can't do the maths or math correctly to convert Metric millimetres in to old Imperial Inch fractions...

I've actually written to Filofax USA more than a few times pointing out the errors on their website.

So in a lazy afternoon moment I constructed a table to show how and why they get the measurements wrong:

Fraction Imp mm mm Filofax Ring Sizes
1 / 16 0.0625 1.5875 1.6
1 / 8 0.1250 3.1750 3.2
3 / 16 0.1875 4.7625 4.8
1 / 4 0.2500 6.3500 6.4
5 / 16 0.3125 7.9375 7.9
3 / 8 0.3750 9.5250 9.5
7 / 16 0.4375 11.1125 11.1 11 mm
1 / 2 0.5000 12.7000 12.7 13 mm
9 / 16 0.5625 14.2875 14.3
19 / 32 0.5938 15.0813 15.1 15 mm
5 / 8 0.6250 15.8750 15.9
11 / 16 0.6875 17.4625 17.5
3 / 4 0.7500 19.0500 19.1 19 mm
13 / 16 0.8125 20.6375 20.6
7 / 8 0.8750 22.2250 22.2
29 / 32 0.9063 23.0188 23.0 23 mm
15 / 16 0.9375 23.8125 23.8
63 / 64 0.9844 25.0031 25.0 25 mm
1 / 1 1.0000 25.4000 25.4
17 / 16 1.0625 26.9875 27.0
9 / 8 1.1250 28.5750 28.6
19 / 16 1.1875 30.1625 30.2 30 mm
10 / 8 1.2500 31.7500 31.8

So as you can see there is plenty of scope for who ever fills in the details in Imperial Factions of an Inch on which ever side of the Atlantic they happen to be to get it wrong...

Lets look at the standard size Personal ring size of 23 mm, you will often see this expressed as 7/8" or 15/16" neither of which is correct you have to go to 29/32nds of an inch to get reasonably close to 23 mm.  Similarly 25 mm rings are sometimes described as 15/16ths or 1 inch rather than 63/64ths... I think 1 inch is the accepted 'practice'

Because Filofax (generic) don't go below an 1/16th of an inch in their Imperial measurements you will see that they can easily over or under estimate a ring size.

I wonder when the USA will move to metric measurement.... Steve runs for cover!


  1. I don't think the US will ever convert to metric. We do have metric measurements on some highway signs but it's a rare sight.

    That said, I always consider 25mm to be essentially equal to one inch, as you pointed out, and consequently 23mm is a bit less than an inch and 30mm is roughly 1.25 inches.

    Being one who stuffs his binder to absurdity, I do not concern myself with rings smaller than 23mm.

    Most of us in the US have not the foggiest idea of how big 1mm is, nor do most of us care! Quite sad. I can manage temperatures and lengths, but have little familiarity with weights and volumes.

    Many times the FF usa site is just WRONG. They did not get their math wrong, they just can't be bothered to publish accurate information about the product.

    1. Thank goodness i can check Philofaxy or the FFUK site for correct measuments :)

    2. I can do imperial weights, volumes, and lengths, but trying to convert from Fahrenheit to Celsius in my head is too hard!

  2. What an interesting read!! Very strange how a company can work so differently over the pond :) xx

  3. Noooo I am too stubborn to switch! :-) good post though. Have you emailed this toFFUSA to let them know?

  4. What a great topic for discussion! I thought I was going crazy!! I recently purchased a compact filo. I am in the US. I went on the FFUS website to compare the various binders. The Temperly and Guinea are shown with 2/3" rings. The Regency listed as 9/16" rings. The Osterly shows 5/8" rings. And the Finsbury as 7/16" rings. On the FFUK site all of these binders are listed with 15mm rings. Are you kidding me?

    It is one thing to take liberties with the conversions, but this is beyond sloppy. How can any business show such complete lack of attention to details. I am convinced they think their customer base is just stupid.

    And here I thought my biggest complaint was the lack of pictures/illustrations of the interior of the binders. ESPECIALLY the expensive ones!

    *rant over* (for now)

  5. As an American, I would be very grateful if the US would adopt the measurement system of the rest of the world. I cannot understand why we are so insular on this system which makes more sense because it is more easily understand since it is based on a decimal numbering system.

    1. It was agreed in the USA Congress that the Metric System should be adopted. This was around 1860!

      Here in England many of the Metric measurements have been adopted. A couple of exceptions are miles on the road and pints for drinks.


    2. Pints are an interesting thing. I didn't know until recently that there is such a thing as an 'American pint'; it's roughly 473 mL, smaller than an imperial pint. Some local pubs got in a bit of hot water because their 'pints' weren't the 568-mL pints one would expect in a Commonwealth country and former British colony.

  6. This post and these comments gave me quite a chuckle this am. As being from 'across the pond' and equally frustrated with our US website I can appreciate this. As someone who is quite 'number' deficit (I don't get US measurements or metric) I often stare at the website in dismay wondering just what the heck is 7/16 and 9/16 anyway? In actuality I do know how to measure this out on a ruler but that isn't the point. I just stare at these figures and scratch my head. All I want to know it 1 inch, 3/4 of an inch or 1.25 inches so I can visual the ring size in my head. I do not want to guess, pull out a ruler or waste any more time on it. LOL When I was into Franklin Covey they had a diagram of the various ring sizes and I would look at it and go, 'oh yeah, small, medium and large.' Worked for me! :)

  7. I think the metric and imperial systems work equally well until you have to worry about small measurements. It takes thought to work out whether 11/16ths is bigger than 2/3rds, for instance, while 17.5mm is clearly larger than 17mm.

  8. I first stumbled upon this site about a week ago when I was considering downsizing from a Personal to a Pocket sized Filofax and have been lurking ever since. Thanks to the posts I read here, I decided against the Pocket and decided to purchase a Compact or Slimline instead. While browsing the US Filofax site, I ran into this very issue of trying to figure out exactly how much smaller the ring sizes were, so this post couldn't have come at a better time. Thanks so much!


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