SI vs USC Units in Engineering

[Dr.D]

It is well known that most of the world use the SI system of units while the USA and a couple of other countries continue to use US Customary units (ft-lb-s = FPS or in-lb-s = IPS). The question of which is better is very much a matter of personal preference, but I'd like to avoid that issue. Instead, I want to ask what is (1) being taught in colleges and universities, and (2) what is in use in engineering practice.

(1) If you are a college student or a faculty member, please tell us
- what units system you primarily use
- in what country are you located
- what is your area of study (machine design, thermo-fluids, materials, etc)
- what texts you use for introductory mechanics (statics, dynamics, mechanics of materials)

(2) If you are a practicing engineer, please tell us
- what units system you primarily use
- in what country are you located
- what is your principal area of practice (automotive, HVAC, machinery, etc)
- do you think that your experience is representative of your industry?

If you specify SI units, please tell us whether it is strict SI, or does it include bastard units such as millimeters for length, rather than meters, or bars for pressure or stress, rather than Pascals.

If you specify USC units, is is primarily FPS or IPS units?

Let me say again that I hope to avoid a discussion of the relative merits and demerits of each system. I only want to inquire what people are learning in college and using in practice. Thanks.

 

[PhanthomJay]

It is well known that most of the world use the SI system of units while the USA and a couple of other countries continue to use US Customary units (ft-lb-s = FPS or in-lb-s = IPS). The question of which is better is very much a matter of personal preference, but I'd like to avoid that issue. Instead, I want to ask what is (1) being taught in colleges and universities, and (2) what is in use in engineering practice.

(1) If you are a college student or a faculty member, please tell us
- what units system you primarily use
- in what country are you located
- what is your area of study (machine design, thermo-fluids, materials, etc)
- what texts you use for introductory mechanics (statics, dynamics, mechanics of materials)

(2) If you are a practicing engineer, please tell us
- what units system you primarily use
- in what country are you located
- what is your principal area of practice (automotive, HVAC, machinery, etc)
- do you think that your experience is representative of your industry?

If you specify SI units, please tell us whether it is strict SI, or does it include bastard units such as millimeters for length, rather than meters, or bars for pressure or stress, rather than Pascals.

If you specify USC units, is is primarily FPS or IPS units?

Let me say again that I hope to avoid a discussion of the relative merits and demerits of each system. I only want to inquire what people are learning in college and using in practice. Thanks.

Practicing structural engineer in USA, primarily use USC, FPS units. I think this is very representative of the civil/structural engineering industry across the US for projects within the US, and likely will remain so for years and years to come.

 

[Dr.D]

@PhanthomJay : Thanks for your comment.

 

[boneh3ad]

Engineering professor in aerospace and mechanical. I use almost entirely SI units in my work except when it comes to building hardware, where I use USC units in order to make procurement and manufacturing easier. The science is all SI. In class, I'd say it's about 75/25 SI/USC. I only ever teach the USC units because they are still so common in industry. Otherwise, I'd stick to SI because it seems to be easier for students to handle when it comes to dimensional analysis.

 

[Dr.D]

@boneh3ad Thank you for the comment. Would you tell us what country you are in, please?

 

[boneh3ad]

@boneh3ad Thank you for the comment. Would you tell us what country you are in, please?

U.S.

 

[Dr.D]

@boneh3ad Thanks.

 

[cosmik debris]

Here in NZ we use SI for almost everything. Exceptions are, babies weights are in pounds, millimetres are used in building and construction, pressure gauges are often in multiple units i.e. PSI, bar, pascals.

Cheers

 

[gmax137]

Practicing engineer in USA, nuclear power generating plants, mostly mechanical engineering (heat transfer & fluid flow). Primarily use USC, FPS units, but plenty of minutes (like liquid flow in gallons per minute "gpm") and hours (steam flows in pounds per hour "pph"). One outlier is the plant output, always in MW. Maybe that's because the electric generators were always in watts / kilowatts / megawatts.

I think this is very representative of the power gen engineering industry across the US for projects within the US.

For projects outside the US we usually do our calcs in USC and then report results in both USC and SI.

The real nuclear part of the work (core design, reactor kinetics, etc.) is rife with "bastard" units like barns (10^-24 cm^2) and worse (linear heat generation rate is always kw/foot).

Dimensioned drawings of components are usually in inches and decimals (e.g., 1.250 inch). Piping isometric drawings are in feet - inches & fractions (ecchhh I hate them). SI dimensioned drawings are in mm. I think that is to avoid 1/4 inch sized stuff showing as 0.00635 meters, too many leading zeros).

 

[russ_watters]

Practicing HVAC (mechanical) engineer in the USA. I use mostly USC except when dealing with foreign clients/products and then I switch to SI. It can be even more complicated than that though since there is overlap between electrical and mechanical when it comes to energy, and electrical is all SI.

In college (in the late '90s) it was probably 2/3 SI except for when I started off in aerospace, which was almost exclusively USC.

 

[Dr.D]

@cosmik debris, @gmax137, @russ_watters

Thanks to each of you. This is very interesting, and I hope that we hear from many more.

 

[mfb]

or does it include bastard units such as millimeters for length, rather than meters

Huh? Millimeters are just meters with an SI prefix.

(1) being taught in colleges and universities

Exclusively SI. Germany.

2) what is in use in engineering practice.

I'm not an engineer, but SI as well in Germany.

In particle physics everywhere, the SI is used for detectors and similar engineering-related measurements. For particle processes: Energies, masses, temperatures and momenta are given in eV, cross sections in barns, times and lengths in SI, always with suitable prefixes of course.

 

[Dr.D]

I thought I had made it clear in my question that I was asking practicing engineers and engineering students about this matter. The SI bias of physicists is well know to us all, and I never would ask such a question of them.

 

[mfb]

My main point were the millimeters, and I mentioned that engineering students in Germany learn SI.

 

[JBA]

I am in the USA and a design engineer for 40 years until retirement in 2005 and worked for a manufacturing company with international sales for the last 20 years and always used USC because the largest number of personnel both technical and others were, and still are, educated with the USC system; and, the manufacturing machines in our USA plants are USC as well. Our company product brochures and technical documents often include both USC and SI units to make them user friendly for both system users.

 

[Dr.D]

@JBA Thanks for the comment.

I wonder where the students are? Thus far, we have heard only from those already at work (or retired), I think. Students, please speak up!

 

[cosmik debris]

Here in NZ we use SI for almost everything. Exceptions are, babies weights are in pounds, millimetres are used in building and construction, pressure gauges are often in multiple units i.e. PSI, bar, pascals.

Cheers

Oh and I forgot, circuit boards

@cosmik debris, @gmax137, @russ_watters

Thanks to each of you. This is very interesting, and I hope that we hear from many more.

I did forget one unit which I imagine is common to many of us. The spacing between pins of integrated circuits when laying out circuit boards is 0.1 inches.

Cheers

 

[PhanthomJay]

@JBA Thanks for the comment.

I wonder where the students are? Thus far, we have heard only from those already at work (or retired), I think. Students, please speak up!

Where have all the students gone, long time passing? Hearing none, I asked a couple of my coworkers (structural engineers) who graduated from US schools about 5 years ago, as to what units they used in their engineering courses. It is exclusively US units in structural engineering . All latest US Codes (steel, concrete) do not even reference SI units. Statics and Dynamics, however, use both systems, and Mechanics of Materials touches on SI but the emphasis is on US units.

 

[Dr.D]

@PhanthomJay That's interesting; thank you for asking around. My own daughter is a structural engineer, and she to uses USC exclusively.

Your opening line, "Where have all the students gone, long time passing?" makes you sound like an old man, almost as old as I am. Surely not, but it really caught my eye!

 

[PhanthomJay]

@PhanthomJay That's interesting; thank you for asking around. My own daughter is a structural engineer, and she to uses USC exclusively.

Your opening line, "Where have all the students gone, long time passing?" makes you sound like an old man, almost as old as I am. Surely not, but it really caught my eye!

Don't be so sure! I'm older than dirt at age 71. Long time passing.

 

[Mark44]

I'm older than dirt at age 71.

Hmmmph! Young whippersnapper!

 

[PhanthomJay]

Hmmmph! Young whippersnapper!

You are looking pretty young there on that mountain, the streams of which please me more than the sea...! Guantanamera!

 

[Mark44]

You are looking pretty young there on that mountain

I try to stay fit so that I can go in the places like the one in my avatar.