I think most of us on the Forum are aware enough that the case size of a watch is not the only factor in determining how big a watch wears on the wrist, nor even the most important factor in some peoples' eyes. Lug-to-lug measurement, case depth, the metal used etc. can all have a big influence on the feel of how big a watch is.

But it got me thinking: Is there some way to calculate the size of a watch taking all of those factors into account? So to create some sort of index to provide a rough guide of the relative size, based on a weighting of the factors at hand. So I did some workings which I have oh-so-modestly called The T&B Index. "Maths" would be a generous way to describe it ("Math" would be an ever worse way to describe it )

The first thing I did was to use my CW watches as the sample. Across the watches I own and whether they are on a strap/bracelet (an important factor I'll come back to later), I tried 11 combinations and ranked them according to what my gut feel told me felt 'biggest' to 'smallest'.


Now of course there's a HUGE amount of judgement in this ranking - I might need to go back and revisit it - but it's a good starting point. Note that, for me, a watch will feel smaller because it's on a strap compared to a bracelet. Take the Sealander GMT, for example, where on a bracelet it feels like a bigger watch than the Atoll 300 on a strap, even though the case size is smaller.

The next job was to add three factors, well-known to us all, that help determine how big a watch wears (NB: Not the only three factors that exist, just three that I felt were quite important):

- Case size
- Lug-to-lug measurement
- Case depth


Now the question became, which of these factors is most important in determining the overall size of a watch? I did a bit of unscientific analysis which basically compared the rank of each of case size, lug-to-lug and depth against my ranking above. This yielded the following results:


My feeling is that if there is a lower variance between my rankings and the respective ranking measure (e.g., case size), then it's a more important factor in determining the relative size of a watch. So I used the total sum of the rank differences to guesstimate what the relative importance of each of those factors is.

My assumption was:

• 50% of the size is determined by case size

• 30% of the size is determined by lug-to-lug measurement

• 20% of the size is determined by case depth

Using this maths, I came up with a modified value for the relative size of the watches (the "Initial Indexed Value"). Re-ranking the watches according to this value and comparing against my initial ranking, I appear to get a bit closer on the ranking variances:


The largest variances in ranking were for the Bel Canto and Lumiere, and I reasoned this was because they're titanium rather than steel or bronze watches, and thus weight must be playing a factor. Of course I could add "watch weight" as a data point, but while it's data that are available for most/all CWs, it's not readily available for lots of other watches, and I didn't want to introduce a factor which might delay or prevent the inevitable worldwide popularity of this measurement index ( ). So instead I just added a Metal Weight Factor of High or Low, to be added at the user's judgement.

I also added a strap/bracelet factor because of my previous assertion that watches feel a little smaller if they're on a strap compared to bracelet. This resulted in some deductions to the Initial Indexed Value, as follows:

• If the watch is on a strap, deduct 3% of the Initial Indexed Value

• If the watch is a lighter metal, deduct 0.5% of the Initial Indexed Value if it's on a strap, or 2% of the Initial Indexed Value if it's on a bracelet

Now you can see I am a bit closer in terms of rank differences. And here I have stopped. My current formula for calculating the relative size of a watch is:

• 0.5 x Case Size PLUS 0.3 x Lug-to-lug PLUS 0.2 x Depth

• Minus 3% of that figure if the watch is on a strap

• Minus EITHER 0.5% or 2% of that same figure if the watch is a lighter metal and depending if it's on a strap or bracelet

In order to take it further I want to re-assess my initial rankings based on wearing the watches, and test this out a little on watches of other brands. But I have concluded, thus far, two things:

• Based on my CW watches, any watch above a 39.89 or below a 34.36 Revised Indexed Value is likely too big or small for me, since these are the CWs that are at the extremes of the range for me.

• It's probably easier just to go and try watches on to see how big they are.

An outstanding piece of watchie exploration!


I think @welshlad has a bigger spreadsheet than you though.
Just saying......

I will study your analysis in detail later, when time allows.

I thought conventional wisdom is that retired folk have more free time than busy workers. You have demonstrated this is not the case - a slow day at work?

A couple of other factors that I think influence my thoughts on this…

1. Dial size
2. Complications and other stuff visible on the dial

Neil

missF wrote: ↑Thu May 15, 2025 6:22 pm I think @welshlad has a bigger spreadsheet than you though.
Just saying......

I hope spreadsheet is not a euphemism.

nbg wrote: ↑Thu May 15, 2025 6:53 pm A couple of other factors that I think influence my thoughts on this…

1. Dial size…

Beat me to it!

For me, it’s not absolute dial size, as I’m quite happy wearing 33 mm vintage watches. It’s more the proportion: size of the dial as a percentage of the total diameter, or dial to bezel ratio. For me that ratio has to be high, which is why I prefer watches without calibrated bezels. They’re generally more elegant.

I’m fine with a watch like the Speedmaster or the Sealander GMT, because the bezel is relatively narrow, but I find a tiny dial surrounded by a very broad bezel off-putting. Especially when the tiny dial effect is compounded by thick hands, as in some dive watches. Most inelegant.

Maybe I should start thinking about the AEF table…AVO Elegance Factor?

nbg wrote: ↑Thu May 15, 2025 6:53 pm I thought conventional wisdom is that retired folk have more free time than busy workers. You have demonstrated this is not the case - a slow day at work?

Tried them on first thing this morning, did the analysis over lunch

There are of course countless other factors that could influence it such as dial size, proportions, domed crystal etc. Even dial color has an impact; I have two watches that are otherwise identical except that one is eggshell and the other dark blue, and the eggshell wears bigger. But I wanted to keep it simple(ish).

An interesting analysis, just the sort that interests me as well!

I've been doing a simpler sort of analysis but focusing on different metrics that are important to me:

1, I'm not particularly concerned about diameter, I'll happily wear anything from 37 to 44mm
2, the ratio of dial size to case size becomes more important as the case size decreases; a larger ratio makes for a more wearable watch
3, The ratio of height to case size again becomes more important as the case size decreases; a 14mm height on a 42-43mm watch is more wearable than on a 40mm one
4, I've found that a simplistic measurement of case volume, calculated as a cylinder using just case diameter and height, also gives me a good feel for how how chunky a watch feels.

I've been maintaining a similar spreadsheet of my watches (past and present, I no longer own many of these...). This is it with the watches sorted by descending case volume:



A Seiko Turtle really is a chunky boy, but so were the Trident MK2 and 3's! Basically I prefer slimish, lowish volume watches irrespective of their diameter. Hence my current love affair with Nomos and the smaller/slimmer CW models such as Sealanders and new Tidents; although I'll always make an exception for my Speedie.

Is there still a "Post/topic of the year" award? I think this OP would make the final for sure!

Thanks for doing this extensive piece of investigation Michael, I’m very supportive of scientific research and would like to assist you if possible. Therefore let me present my own work in this field that I have recently concluded.

Introduction

The way of determining the overall size of a watch is determined by many factors. In response to a scientific paper recently published on the CW forum on this subject, this author has taken the theories presented and cross referenced them to other sources of data in this area of research. The aim of this work is to determine if one method for determining watch size is more accurate than another.

References

Usually references are at the end of a document, however in order to assist the reader they are presented here so the flow of the post is not interrupted. Note when reference is made to these in the rest of this post, the number of the relevant reference will be placed in brackets.

(1) The T&B Index (a.k.a “How big is a watch?”) - @timepieces_and_bags, 2025
(2) What about dial size/I was just going to say that - @nbg & @Amor Vincit Omnia 2025
(3) Case volume - @timor54 2025
(4) CW forum member iain’s world renowned database of common sense - @iain 1974-present

The Watches

In order to make this work manageable, the full collection of the author is not going to be used. However unlike other researchers in this field that only focus on watches currently in their collection. The author has selected their oldest and newest watch to ensure they encompass the entirety of their watch ownership. As all watches they have owned are covered by this time frame this makes the conclusions from this research far more accurate (4)

Therefore the watches chosen for this research are the IWC MKXVIII (Mk) and the IWC vintage Aquatimer (AT).

Method

The method pioneered in (1) was first used to determine which watch was biggest.
Gut feeling AT biggest, Mk Smallest.
3 factor method Mk – 40mm diameter, 51mm lug to lug, 11 depth. AT – 44mm diameter, 51mm lug to lug, 14mm depth. AT Biggest, Mk smallest
Strap/material fudge factor - Mk bracelet/steel, AT strap/steel. AT Biggest, Mk smallest
Conclusion AT bigger than the Mk

Next the method in (2) was used
AT dial size is bigger than the Mk, conclusion AT bigger than the Mk

Method (3)
The volume of the case of the Mk is only around 70% of the volume of the AT. Conclusion AT bigger than the Mk

Method (4)
While this method does not require any measurements, it does rely on over 50 years of comprehensive data so can be considered the more accurate of all the methods selected (4). Using this technique to determine which was the biggest also took the least amount of time. Within milliseconds this technique was able to determine the AT was bigger than the Mk.

Conclusions

Irrespective of which method was selected the outcome was the same. Therefore the author has concluded that the reason the AT looks bigger than the Mk is because the AT is bigger than the Mk. If you want scientific proof then you can take time to carry out measurements and calculations, however if you have access to a similar level of data as (4) then you may also be able to conclude quickly whether one watch is bigger than another.

@iain
Brilliant!

RichM wrote: ↑Thu May 15, 2025 9:42 pm Is there still a "Post/topic of the year" award? I think this OP would make the final for sure!

After some discussion it was discontinued in 2018.

^^^^ We do of course have the thread reference thread which all forum members are encouraged to add their favourite threads to.

@timor54 - a thoroughly pleasing analysis which I will ponder on to see if I can incorporate it into my own workings.

@iain - thank you also for your detailed testing which does support my second conclusion of "It's probably easier just to go and try watches on to see how big they are."

However, sometimes due to time or distance constraints (or a largely online-only business model) we also sometimes don't have the luxury of trying on watches in advance. Of course this is a bit of tongue-in-cheek analysis, but in a semi-serious way I was pondering why I have owned some watches of a 39mm case size which have seemed too small, while others have seemed large enough. And the opposite being true at the larger end of case sizes. Now that obviously comes down to other factors such as thickness, weight etc., and I wondered whether it might be helpful to be able to guesstimate in advance whether a watch at those more extreme ends would still be within an acceptable size taking all those other factors into account.

Thus, dear student, unfortunately you've provided the right answer to the wrong question. The question you have answered is "Which watch is bigger than the other?" The question I'm trying to answer is "How can one determine the relative size of watches compared to one another?" C+.

@timepieces_and_bags C+ I’m happy with that, it’s higher than my usual academic efforts.

However I would argue that the question I answered was “Is a scientific method a better way to determine watch size?”

My conclusion could be interpreted as your scientific theory is certainly one method, but trying on a watch works just as well.

But then again it could a be equally interpreted as my database of common sense is only reliable when it comes to spotting the bl**dy obvious.

iain wrote: ↑Fri May 16, 2025 1:14 pm However I would argue that the question I answered was “Is a scientific method a better way to determine watch size?”

My conclusion could be interpreted as your scientific theory is certainly one method, but trying on a watch works just as well.

Undoubtedly we're in agreement that the answer to that question is "No" and trying on a watch is simply the only way of knowing the true size, all things (especially the incalculable AVO Elegance Factor) taken into account. But I live quite far from both Maidenhead and Texas!

timepieces_and_bags wrote: ↑Fri May 16, 2025 1:57 pm

iain wrote: ↑Fri May 16, 2025 1:14 pm However I would argue that the question I answered was “Is a scientific method a better way to determine watch size?”

My conclusion could be interpreted as your scientific theory is certainly one method, but trying on a watch works just as well.

Undoubtedly we're in agreement that the answer to that question is "No" and trying on a watch is simply the only way of knowing the true size, all things (especially the incalculable AVO Elegance Factor) taken into account. But I live quite far from both Maidenhead and Texas!

Not so fast, you have forgotten that perception trumps reality (whatever that may be) every time. The way you perceive a watch on your wrist is not a static thing, it develops over time. So the 44mm monstrosity yesterday could well be the 44mm favourite today!