Precision in fractional inches


In metric units trailing zeros (after the decimal mark) are used to express precision. 100 mm can be anything between 99,5 mm to 100,5 mm while 100,0 mm is anything between 99,95 mm and 100,05 mm.

Can you similar to this write 6" 0/32 to denote you the value has a precision of 32nds of an inch, or does 0/32 just look weird?


0/32 looks weird. I think for fractional inches, if precision was of interest, you’d put a note on the plans indicating something like, “Dimensions to nearest 1/32 in.” or something like that.

The plans I create for furniture projects usually are done in fractional inches. The precision would be dependent apon what the builder uses for measuring. I model to 1/64 in. precision in SketchUp but rarely have dimensions smaller than 1/16 in. Wood changes dimension enough with changes in relative humidity and temperature that it doesn’t make sense to get too tight with the precision when actually cutting.


The idea was to subtly suggest a precision for user input in a text field. Seems like that can be ruled out for fractional inches then.

Do you have rulers in the US that does not have a metric scale on one side? I have seen rulers in Sweden with only metric units but the ones with both imperial and metric seem to by far be the most common.


There are rulers and tape measures that only have inches on them. I have a yard stick (36 inches long) that is only marked in inches. They aren’t as common as they once were, though.

I would expect to see more concern about precision in engineering drawings which if presented in inches would be decimal inches. You’d also be more likely to see tolerance indications, i.e. 3.625 ±0.002.

For construction, precision might be to the nearest quarter or eighth inch but the way construction materials are, that’s about the best you could do.


Most scales (rulers) in US are either imperial or metric. I’ve never seen a combination one. The metric one mostly resides in a drawer, as it’s seldom used by most people unless they do work overseas. There are also separate imperial scales called “architectural” and “engineering”. Architectural reads things like 1/4" = 1’-0" while Engineering ones read like 1"=20’. The engineering scale is mostly used for site plans, but the edge with multiple thirds of an inch could be used on architectural drawings for modular brick courses or for 16" O.C. spacing. (A brick course is 1/3 of 8" and 16" is 1/3 of 4’)


Really? I have two on my desk.




That could work.


I guess anyone using Häfele hardware or the like needs to switch back and forth at a moment’s notice.

I do have a combination English/Metric 25’ tape measure.

BTW, what’s magical about 32 mm that gets little diamonds along the tape?


Standard 32mm spacing is used for shelf pin holes.
For more, see:


Combination imperial/metric rules and tape measures (as illustrated above) are very common in the UK.

Most new stuff is dimensioned in metric, but there are a LOT of older buildings, woodwork, and other manufactured articles still around that were designed and built in imperial length units.

We ‘converted to metric units’ by Act of Parliament in 1968 - but far from completely. Road distances are still measured in miles, signs for the distance to the next motorway exit are in yards, and although timber is now sold in ‘metric’ sizes the old ‘imperial’ units are still used to describe it - wood called 2x1 was 2in x 1in sawn, and the planed all round (PAR) finished size is about 1 3/4in x 7/8in, or 44 x 22mm, often sold as 50x25mm nominal.

I do a lot of work on scenery at our local amateur theatre,, and because much of our scenery is very old (not even new when I joined in 1970) we still build most new scenery to fit the old flats and rostra which are typically dimensioned as a whole number of feet (or a multiple of 6inches) - hence almost all our tape measures in the theatre workshop are dual units - metric AND imperial on one tape.

You can buy ‘pure’ metric or (less commonly now) ‘pure’ imperial rulers and tape measures of course. Most builders and the whole construction industry now use metric dimensions for new buildings, but might need to match older imperial dimensions if doing restorations of old buildings.


We’re in a weird Hybrid world such that the now metric sheet wood sizes are the equivalent to the original imperial counterparts. I wonder if we had begun metrically, what an 8’ x 4’ would of been, probably not 2440 x 1220, maybe 2400 x 1200? When I worked at the BBC they even had a custom scale rule of 300mm which was known as a “metric foot”, a compromise of sorts. While I’m hardwired for Imperial units, it’s sure a lot easier to work in 10’s.


I wonder if it’s because of the sheer size of the US economy that wood products manufacturing equipment (for sheet materials like plywood and fibreboard products) were designed for that market first, and the cost of change is too high. I believe that high cost and low benefit was why the UK didn’t change road distances from miles to km - though Canada did decide the opposite. I wonder why?


There’s a nice book which relates to the Imperial/Metric side of this discussion, for those who might be interested in that stuff…

Whatever happened to the Metric System?: How America Kept Its Feet
by, John Bemelmans Marciano

Link goes to Audible’s Audiobook… where there’s a 4.5min sample to listen to…

In spite of it’s sub-title it’s not entirely focused on America’s experiments with the Metric System.

That story is told, but in laying out the historical framework so that it can be, the Author ultimately spends a majority of the time dealing with the many other international standards which have both been adopted, and rejected in much/most of Europe.


It must be a cultural preference? Road sign costs would be pricey if they all had to change at once, but as they get made and replaced with time, phasing them to metric wouldn’t be such a hit.

The currency conversion in the UK seemed to hold and makes life easier to now work in 10’s and not 12’s (12 pennies = shilling !) I’m not sure if people would want to go back to that.
Weight, still spoken of in “Stones”, x 14 pounds, We can trace back to the origins but maybe better to have it line with other more standardized weights?

Ultimately it doesn’t matter what the units are, they could be seen as arbitrary, but it’s what is familiar to people and as such the terms of how they understand the world around them, much like a language?


The real story is that the fractional units had been used for centuries but they had huge variations from region to region. When they were finally standardized the standard was based on metric units with the inch set to 25.4 mm.


The units might be arbitrary, but how they are defined is very important to science as more and more accuracy is needed. Today, the scientific community has standardized almost all units of measurement and based them on physical constants that are considered universal. When I was a kid the meter and kilogram were still based on pieces of metal stored in Paris, but some years ago when I had the chance to visit our local metrology lab all they used were weird collections of prisms and lasers.



The guy is probably destroying it by breathing on it!


… so the final corrosion factor might come down to what his preferences are for a mouth wash?

Peppermint, Spearmint, or Winterfresh?