Imperial vs Metric

I am working on a medical oriented application that needs to service measurements in both Imperial(US) and Metric values

For height(distance) the US values would be Feet/Inches, and the Metric would be in cm
For weight the US would be pounds, and the Metric would be kg

But there is also a need to store the Systolic and Diastolic blood pressure values… and there in lies my question
In the US these are measures in mm/HG (millimeters of mercury), but my research shows a metric unit of kPa (

and for Blood Glucose, the US measure as “mg/dL” where the metric measurement is “mmol/L”

So I need to decide if for those users that would use Metric, if I should just use ALL US units, or ALL Metric units
or allow the user to select a unit type for each item being measured

ie. for Blood Pressure which is more common (outside the US)… “mm/Hg” or “kPa”?
and for Glucose which is used more “mg/dL” or “mmol/L”

Right now, I have it set to either
US values as “feet/inch” , “pounds”, “mg/dL” and “mm/Hg”
Metric values as “cm”, “kg”, “mmol/L”, and “kPa”

I think in German we have mmHg for blood pressure.
Something like 120/80 is common blood pressure.

And we use mg/dl for blood glucose here.

So you better make it selectable.

I live in a mostly metric country. height is cm, weight is kg, blood glucose is mmol/L (your usual 72 is 4.0 to me - blood glucose ( or more recently as with the Freestyle Libre and a few lesser know devices, interstitial fluid glucose) meters are most often configurable in either unit system). Blood Pressure however is still most often mm Hg. Newer electronic devices are configurable, but most often mm Hg. (not mm/Hg. You don’t “divide by mercury”.) Breathing apparatus such as CPAP will generally use cm H2O instead of mm Hg.

I would suggest that you let the user select the unit system for each type of measurement.

It’s been the metric system here in Oz since 1970. Although, if you asked me how tall someone was, I’d give the answer in feet!

As suggested by Christian and Lous, let the user select the unit system for each type of measurement.

Thanks… that is what I will do… each measurement type will be selectable to be expressed in either unit type

Science uses the metric system (SI, Systme International), all around the world. So, I would risk to say, accept as desired, convert it to SI if not standard, store as SI. To show: If display is not set as metric (SI), convert values as necessary, display as desired. USA is the most unusual place in the world in relation to the metric system, so check with the local medical community, but I’ll find weird if you have exceptions for medical data archiving.

The medical data is “personal data”, as in it is entered by the user for the benefit of the user… but my intent is (and had been) to store the data always in metric form, and the preference options would simply control how it was displayed, and if a conversion was necessary prior to writing to the database.

And really the only reason I even broached this subject, is for the benefit of users not in the United States, to give the app hopefully a wider user base.

Software and reality.

Softwre: to sold it, you have to do what you said.

Reality: the current (since…) measures are no more the Imperial Units.

Read: Imperial Units .

When will people stop using deprecated old units. I think the NASA had a crash lately (years ago) because someone used oldster deprecated Units instead of metric system.

Who remembers the measuring unit bent ?
(the old Egyptian measuring unit)

Actually, I believe that screw up was when using the Metric System. Being unfamiliar with the units, he put the decimal point in the incorrect position!!!

All great things can be said about the metric system, but it can all come undone (and I have done it) when the decimal point is in the wrong position. Easy enough mistake to make when doing mental calculations.

Australian doctor here. Almost all medical measurements in Australia (and other countries outside of the US that I have worked) are in metric.

Except blood pressure. The correct metric term for pressure is Pascals (Pa) or kiloPascals (kPa) but blood pressure measurement in mmHg is so ingrained around the world that I doubt it will ever change. This is because the most accurate way of measuring BP (externally) is with a sphygmomanometer, which has an actual column of mercury. I would not even bother to present Pa as an option.

For blood glucose levels (strictly speaking it is concentration) both mg/dL and mmol/L are metric but the correct SI (Systme Internationale d’Units) is mmol/L and that is what is used in Australia and much of Europe.

Thanks Rob…
I have decided on offering the following options

  • Blood Pressure readings - either mm/Hg or kPa , but as you mentioned I bet 99.9% will stay with mm/Hg
  • Glucose readings - either mg/dL or mmol/L , mg/dL is what is used in the US (and apparently Germany according to Christian)
  • Weight - either pounds (lbs) or Kilos (kg), at users discretion
  • Height - either feet or cm again, at users discretion

Each of these four items can have either unit selected, so its not an all US or all Metric situation

Thanks for all the input,

Rob… I “assume” that A1C is universal as expressed in percentage?

You might want to add m to your height option. In NZ we measure adults in m while children up to 90cm (strange that’s about 3ft) use cm.

I concur with Rob, although I should mention that the UK has its own idiosyncrasies - end tidal CO2 in kPa, but Australians generally like mmHG (I suspect you don’t need that one)

In Australia, we tend to use cm for adults as well as children

I thought about that, but numerous articles I read, said the most acceptable way was to express in “cm”, since the difference is the inclusion (or exclusion) of a decimal point. and most people will be under 2 meters since that is 6’6" which is rather tall

[quote=392534:@Dave S]
Rob… I “assume” that A1C is universal as expressed in percentage?[/quote]

Yes, HbA1c is a percentage of haemoglobin that is glycated, so always a percentage (of total haemoglobin). This is a ratio, so not metric or imperial.

In metric it doesn’t really matter which multiple you use - so height can be cm or m. My height is 1.83m = 183cm = 1830mm - metric is easy.

I’m not sure what your app does, but another useful measure is the Body Mass Index (BMI). Weight (in kg) divided by height (in m) squared. It is used as a measure of obesity as it adjusts for a person’s height. A BMI between 20-25 is considered healthy, 25-30 is considered overweight, 30-35 is considered obese, and above 35 is considered “morbidly obese”. The BMI is not a perfect measure as someone could be very muscular and have a high BMI, but the vast majority of people with a high BMI are not muscular, just obese. The units for BMI are technically kg/m2 (meter squared) but are usually not included.

Do you have a list of units that you haven’t mentioned that you wish to discuss?
I suspect you are just looking at BMI and diabetic management.
I can give you the formula for fat free mass if you think that would be useful. It is interesting how many people freak out when they realise just how much of their total body weight is fat!

Now that’s why my Dr tells me I’m not tall enough :slight_smile:

We all talk about miles-per-gallon but buy in litres in the UK
So it’s now difficult to quickly know how far the fuel you just bought will take you.
Horrified to find that the current £ per gallon figure is nearly £6 :frowning:
And UK gallons arent as big as US gallons!!

This app is designed to track personal medical information…

  • Glucose readings (I’m type 2 and send a report to my Dr. once a week), this will include real A1C, as well as an “estimated” A1C based on an analysis of readings (not as accurate of course, but provides a “trend”
  • Blood Pressure, Systolic/Diastolic and Pulse rate (including calculated MAP
  • Weight / Height which will allow for BMI
  • track all medications current and past (since each Dr always asks for a current list)
  • allergies
  • past medical conditions
  • immunizations
  • emergency contacts
  • healthcare provider contacts
  • reports, graphs, emails, etc. etc.

And before someone says it, yes I know there are dozens of similar apps, but I have yet to find ONE that does all of these things (usually its 3 or 4 apps with inconsistent overlaps), and/or they require InApp purchase, or have constant popup ads or you have to sign up to same cloud service.

So, these are (I believe) all the measurements I need, my main interest was in how there were express outside the US, and your responses have pointed me in the right direction… And I have all the equations for MAP, BMI, A1C as well as the various conversions from one unit type to another… Thanks

Hey Dave,

Good luck with this project. Can I suggest you also add blood type & donation history (in NZ I donate whole blood & plasma, but some people can donate whole + platelets or just platelets/plasma).

Are you going to distribute mobile + desktop?