How do you convert non-metric distance units?

[Bart_van_der_Wolf]

Hi folks,

Here's one for the weekend.

Units of length
"The system for measuring length in the United States customary system is based on the inch, foot, yard, and mile, which are the only four customary length measurements in everyday use", according to Wikipedia.

I have a question, which may seem odd at first glance, but there is a reason for asking. I'm writing, amongst others, a software routine that converts between units of length. I also know there is probably not a definitive answer, so I'm looking for feedback based on everyday normal use. This is not a trick question, so all answers will be considered in my final evaluation, and encoding.

Now, with that out of the way, here is the question.

When do you, in everyday use, switch from inches to feet, and when from feet to yards, and when from yards to miles?

I know that 12 inches equals 1 foot, and 3 feet equals 1 yard, but do you usually say e.g. something is 36 inches or 3 feet, or one yard, long or distant? Or are inches used to avoid fractional feet ('x' feet and 'y' inches)? Or is it context dependent, e.g. when talking about precise measurements you use the smaller unit of length? Or are you not an engineer and convert everything to the largest practical unit, 'x' feet and a bit (but then when does the bit become large enough to give it more meaning, like 'give or take an inch')?

The same for yards and miles, but maybe the same principles apply?.

Thanks in advance for some soul-searching (or maybe there is an official recommendation?) and any resulting useful feedback you may have to offer.

Cheers,
Bart

 

[Doug Kerr]

Hi, Bart,

Here's one for the weekend.

Units of length
"The system for measuring length in the United States customary system is based on the inch, foot, yard, and mile, which are the only four customary length measurements in everyday use", according to Wikipedia.

I have a question, which may seem odd at first glance, but there is a reason for asking. I'm writing, amongst others, a software routine that converts between units of length. I also know there is probably not a definitive answer, so I'm looking for feedback based on everyday normal use. This is not a trick question, so all answers will be considered in my final evaluation, and encoding.

Now, with that out of the way, here is the question.

When do you, in everyday use, switch from inches to feet, and when from feet to yards, and when from yards to miles?

I know that 12 inches equals 1 foot, and 3 feet equals 1 yard, but do you usually say e.g. something is 36 inches or 3 feet, or one yard, long or distant? Or are inches used to avoid fractional feet ('x' feet and 'y' inches)? Or is it context dependent, e.g. when talking about precise measurements you use the smaller unit of length? Or are you not an engineer and convert everything to the largest practical unit, 'x' feet and a bit (but then when does the bit become large enough to give it more meaning, like 'give or take an inch')?

The same for yards and miles, but maybe the same principles apply?.

Thanks in advance for some soul-searching (or maybe there is an official recommendation?) and any resulting useful feedback you may have to offer.

In the US, There is very little broad standardization of practice in the general case. Of course, in a certain aircraft plant, there may be norms de maison for use on certain types of drawings or in certain types of textual documents.

Actual practice in the US varies with the situation and within a given situation.

For example, in stating the stature (height) of a person, it is most common to state it in feet, inches, and "binary" fractions of an inch, as "6 feet 2-1/2 inches". Less common is inches and binary fractions: "74-1/2 inches".

Typically the length of boards of "dimension lumber"' lengths of pipe, and so forth, as bought from a lumber yard or such, are given in integral feet: "a length of 3/4 inch iron pipe 8 feet long." The same would be true of lengths of rope: "I'll have 100 feet of that yellow nylon rope, please." But when the plumber asks his assistant to cut a length of that pipe and thread it, almost always the dimension would be stated in inches and binary fractions.

Most engineering drawings for mechanical parts (when using US customary units) state dimensions in inches (with decimal fractions) up to perhaps 120 inches or so.

Dimensions on an auto, when stated in US customary units, are usually in inches, with decimal fractions as appropriate. ("He had the bigger Land Rover - the 108 inch wheelbase one.")

Distances along a roadway being constructed or modified are given in "stations" (100 feet) and feet (with decimal fractions). (You will see this in painted markings: 26 + 45.45; that is 2645.45 feet from the reference point.)

Architectural drawings, floorplans, and the like are typically in feet, inches, and binary fractions.

If I give the carpet contractor a layout of a room to be carpeted, it will likely be dimensioned in feet, inches, and binary fractions. But (if this is a modest-sized room), the worker are likely to measure and cut in terms of inches.

The dimensions of a room (as for example in a description of the house in a real estate listing) are generally given in feet and inches (perhaps with binary fractions of an inch). But the dimensions of the plot of land will probably be given in feet (with decimal factions).

The nominal dimensions of a mattress were once customarily stated in feet and inches, but today are more likely stated in inches.

The dimensions of a door, as sold by a building supply store, will usually be stated in inches, and that will usually be followed in casual discussion ("Well, the bathroom had only a 24 inch wide door, so we had some trouble getting the new cabinet in.")

Linear dimensions of land are usually given in feet, and for accurate work (as in land surveying) with decimal fractions to a precision of 0.01 foot.

Dimensions of furniture are usually stated in inches with binary fractions.

Precise dimensions are rarely given in yards except in connection with certain sports. However, it is very common to use yards to give estimated distances: "The witness estimated that the car was about 50 yards from the gate when the explosion was heard."

In general conversation, distances are most often stated in miles once they are over perhaps 1/4 mile. Thus I might say that the nearest fire hydrant is about 50 feet from my house, and a certain neighbor's house is 150 feet down the street, while the Lincoln National Forest starts about 1/4 mile down the street.

The "size" of railway rails and overhead crane rails, and the rails of the high speed test track at Holloman Air Force Base (of the crane rail style, as a matter of fact), are stated in pounds (avoirdupois) per yard of length.

Thus it will be very difficult to make a general purpose program for converting between SI units of length and US customary units of length that would "outguess" the practice of the user in whatever context obtained.

I hope this has been of some help.

Best regards,

Doug

 

[Cem_Usakligil]

Great answer Doug, thanks.
What about distances pertaining to photography such as the distance of the subject to camera or the length of the depth of focus?

 

[Bob Rogers]

I think it's mainly context. Doug has a lot of specifics for certain industries. I'll point out an oddity. He mentions door widths are always given in inches (24 inches, 30 inches, etc.) which is true, but door heights are always feet and inches, with 6'-8 being /the/ standard. That's for doors you walk through, not cabinet doors, which are always inches. Pretty much everything in a kitchen or bathroom is measured in inches (except the door ;-)

If I'm talking about how far away something is with my wife, then I use miles. A tenth of a mile, a quarter mile, two miles.

We don't use yards very often, outside of sports.

If I was telling my wife how big something was I would probably use inches if it was under a foot. Over three feet I would probably use feet. In between it would probably depend on how specific I wanted to be.

Funny thing -- when my wife measures for furniture and rugs she uses /her/ feet, which are about 9 inches, to measure. It makes discussions with shop keepers, um, interesting.

I think any really useful conversion tool for inches would need to take and give fractions, since we don't use decimals. So 10-5/8 inches. Outside of engineering, we generally go to the nearest 1/8, but sometimes 1/16.

 

[Bob Rogers]

Great answer Doug, thanks.
What about distances pertaining to photography such as the distance of the subject to camera or the length of the depth of focus?

For me, that's always feet, because that's what's marked on the lens.

 

[Doug Kerr]

Hi, Cem,

Great answer Doug, thanks.
What about distances pertaining to photography such as the distance of the subject to camera or the length of the depth of focus?

The US customary unit scale on lenses is generally in feet (often with decimal fractions).

I think most discussions of distances (in the context of US customary units) will be in feet.

All my depth of field and out-of-focus-blur calculators use SI units, in particular, meters.

Best regards,

Doug

 

[Bart_van_der_Wolf]

Thus it will be very difficult to make a general purpose program for converting between SI units of length and US customary units of length that would "outguess" the practice of the user in whatever context obtained.

I hope this has been of some help.

Hi Doug,

Absolutely! Oddly, yards seem pretty unpopular except in a few situations such as sports, it seems.

That's very helpful information, because it confirms what I already assumed, that there is little formal standardization, but I wanted to verify. I didn't go to school in the US, so I thought that maybe there is a preferred method to teach these things in elementary school, apparently not, or it is soon replaced with more practical use.

Thanks a lot.

Cheers,
Bart

 

[Bart_van_der_Wolf]

I think it's mainly context.

Hi Bob,

Thanks for your input.

If I'm talking about how far away something is with my wife, then I use miles. A tenth of a mile, a quarter mile, two miles.

We don't use yards very often, outside of sports.

Interesting, It seems like most (not all) indoor distances are in inches, outdoor mostly feet, rarely yards, unless large distances are involved, which are expressed in miles.

Funny thing -- when my wife measures for furniture and rugs she uses /her/ feet, which are about 9 inches, to measure. It makes discussions with shop keepers, um, interesting.

LOL. My research already uncovered a lot of historical variation of the actual (foot) measurements, so your wife just follows a good tradition.

Thanks for your contribution to coming closer to solving the puzzle.

Cheers,
Bart

 

[Bob Rogers]

Interesting, It seems like most (not all) indoor distances are in inches, outdoor mostly feet, rarely yards, unless large distances are involved, which are expressed in miles.

That's an interesting observation, and I think you're spot on. I can't think of any situation where yards are used indoors, excepting measuring carpet, which is typically priced in square yards. But that's really an area measurement, and not a distance measurement.

The exception on indoor distances are rugs and rooms which are nearly always measured in feet. So the bedroom in a home listing is 12x14 and the rug you buy to put in it might be 8x10.

Interestingly, the rug might really be metric, making it smaller than 8x10, but they sell it that way anyway.

 

[Andy brown]

I live in the first world where we have been using metric for many, many years.
O.K, facetiousness aside, I live in Australia and yes the U.S is one of the last places on Earth to still maintain the imperial measurement system as the norm.
We usually talk in metric measurements and definitely in celsius temperatures not farenheit.
Older generations (myself) grew up with both systems being used so we can interchange at will.
Speed limits for example are all in KMH but I know all of the speeds in imperial as well, i.e 100kmh is roughly 60 MPH.
We all know that a 300 metre drive in golf is the same as 330 yards (and yes it's metre not meter).
The last bastion of measurements which are still spoken as imperial are a person's height, 5 feet or six feet for example, and photography. Still using 6x4 inches or 8x12 inches.

Pretty much everything else is metric.

 

[Bob Rogers]

As an aside, I think the real reason the US has stuck with the imperial system is the construction industry. There doesn't seem to be a practical means of switching over to metric. Sure, we could rename all the construction parts with metric names, but there wouldn't be any real advantage to doing so. As long as we are using 4x8 sheets of plywood and drywall we're going to use 16 inch stud centers and 12 inch joist centers.

The problem is that in order to switch, all the lumber suppliers would need to carry twice as much inventory for long enough to finish all the imperial system projects in the pipeline. And why would they want to? It think the reason it's so much harder here than other places is because of the extent to which we use wood frame for construction.

 

[Michael Nagel]

Well - I am well within the SI system, but occasionally I have to work outside the SI system. Conversion is fairly easy for units often used, but sometimes unnerving when many conversions are involved (like heat release in kw versus air condition cooling capacity in BTU or similar things). There can be fun playing with strange units like the well-known attoparsec or furlongs per fortnight...

Best regards,
Michael

 

[James Lemon]

Metric is obviously easier to work with mathematically. When you buy a piece of wood at the lumber store the length is still the same regardless of how you measure it. Different in name only! I wonder why decametre isn't used as a reference. I can visualize distances and volumes easier using the imperial system as a reference as opposed to using metric. But then 65 years sounds like a long time compared to hours which works out to approximately five hundred and seventy thousand hours.

 

[Bart_van_der_Wolf]

Well - I am well within the SI system, but occasionally I have to work outside the SI system. Conversion is fairly easy for units often used, but sometimes unnerving when many conversions are involved (like heat release in kw versus air condition cooling capacity in BTU or similar things). There can be fun playing with strange units like the well-known attoparsec or furlongs per fortnight...

Hi Michael,

Yes, it's much easier for those accustomed to SI units. However, even then one could ask oneself why we use centimetres (1/100th of a metre) as much as we do, but rarely decimeters to indicate distance or size.

The answer is probably, and that very roughly also applies to 'imperial' unit users, that many common/everyday measurements/dimensions can be expressed in fewer digits, and with fewer zeroes before and immediately after the decimal fraction indicator (comma or period). That should help to reduce errors in quick judgment and it is more efficient to display.

That striving for simplification, is apparently also used in the 'imperial' measurements, when people seem to e.g. prefer feet and, for the fraction, inches to describe a single dimension. I am a tall person, 6 foot 4 inches, myself.

I have also learned that it helps that the foot produces exact 1/2nd and 1/4th (and 1/3rd, and 1/6th) fractions, when expressed in (fractional) inches.

It is surprising to me though, that yards are apparently rarely used, beside some sports related dimensions. Road signs may even indicate that the next highway exit is 1500 feet ahead, rather than using yards (e.g. 500 yards). That clearly conflicts with the attempt to simplify and shorten numbers ...

Cheers,
Bart

 

[Bob Rogers]

Metric is obviously easier to work with mathematically. When you buy a piece of wood at the lumber store the length is still the same regardless of how you measure it.

Sort of, but if you don't re-enginner it all to be based on metric units then it's harder to work with instead of easier.

As an example, studs are usually 16 inches, on center. In metric, that's 40.64mm. 16" on center is really easy to measure out, but 40.64 would be hard even for someone pretty good at doing math in his head.

A standard lumber length is 8 feet; 243.84mm. Suppose you want to cut it in half; even a high school dropout knows that you want a 4 foot length. Not so easy with the metric.

Now if everything was re-engineered and we used 50mm centers and 250mm lumber, things would become easier in metric. But stocking both sizes in the transition period would be very costly.

 

[Asher Kelman]

Well, how did the transition to metric units work in the U.K.? Did they changer their size of lumber. The standard plywood seems to be sold in mm measurements

18x1220x2240mm or 0.7086x 48.315 inches x 96.63 inches.

So that works out close to 3/4" x 4' x 8' except it just 0.3" and 0.63" extra.

So, I imagine, they just put the wall studs at approx 16" apart but accurately at 409.6 mm apart to go from center to center covering a wall.

For a remodel of an older home, the plywood would need to be cut down slightly every so often to allow for the extra 0.3 inch in width or .63" in height.

Asher

 

[Asher Kelman]

Screws and bolts are even more problematic than distance measurements.

The transition must have been a challenge for fixing cars in the U.K. as both metric and Whitworth threads might be used in the same car that has seen parts updated. I imagine some cars have both as light fixtures become obsolete and need to be replaced with modern versions.

Amazingly, British Morris and MG used metric bolts in their cars but tricked the British motorists by have them fit standard British Imperial Whitworth threads! The only time they found the mismatch was when they tried to replace a genuine bolt with a store bought bolt that matched the wrench size of the head!

Asher