How do the American and British measures of blood sugar compare?

My son has diabetes, and when I do investigations online, I find that American websites talk about blood sugar levels in the hundreds, while my son is encouraged to keep his levels between 5 and 8 mmol/l. Can anyone tell me how the two scales compare, so that I can interpret the info from sites both sides of the Atlantic?!

mmol/l is the unit in the UK, whereas the US use mg/dl.
The unit mmol/l stands for milli-moles per litre. (or liter in the US, I believe). milli means a thousandth, so what is a mole (other than a small rodent-like animal)? A mole is that quantity of a substance whose mass in grams is the same as its formula weight (atomic weight). Each molecule of glucose has 6 Carbon atoms, 12 Hydrogen atoms and 6 Oxygen atoms. A carbon atom weighs 12 units, a hydrogen atom weighs 1 unit and an oxygen atom weighs 16 units. These units are called relative atomic mass units (don't need to go into why). So the atomic weight of glucose is (6x12) + (12x1) + (6x16) = 180. Therefore one mole of glucose weighs 180g. So now we are in a position to look at mmol/l. 1 mmol of glucose is 0.18g. So 1 mmol/l is 0.18g in 1 litre of water.
So now you can see the relationship to mg/dl. A decilitre is a tenth of a litre or 100ml. A miligram is a 1000th of a gram. Therefore 0.18g is the same as 180mg. We are only dealing with a 10th of the amount of water (100ml or 1dl) so therefore can divide this number by 10 giving 18mg/dl. Thus 1 mol/l = 18 mg/dl.

To convert from the American system to the British system, divide by 18, thus:
144 mgl/L divided by18 (conversion factor) = 8 mmol/l
To convert from the British system to the American system, multiply by 18, thus:
8 mmol/l x 18 (conversion factor) = 144 mgl/L

Miz Lamb answered your question very well indeed. Yes, the conversion is 18 as a rule of thumb. So, if your son's reading is 8 mmol/l, to convert this into mgl/L, simply multiply 8 x 18 to get a 144 reading. So, if my reading in mgl/L is 250 my equivalent mmol/l would be (250/18) 13.88. Simply divide 250 by 18 to arrive at 13.88. It is really that simple. Good luck to you and God bless you.

here in America we measure in mg/dL and you do the mmol/L measures. The conversion number is 18. So if you divide my numbers by 18 you will come up with approximate mmol/L. I multiply your numbers by 18 and come up with what I am familiar with