Calibrating g6

When they say not to calibrate the g6 unless it is 20% off what is the measurement in millimoles?

This might help you …

Since 20% is a relative amount, it would vary by the number itself, rather than absolutely. Examples, taking 20% as variance:

5 mmol/L = 1.0, 90 mg/dl = 18.0
6 mmol/L = 1.2, 106 mg/dl = 21.2
7 mmol/L = 1.4, 126 mg/dl = 25.2
8 mmol/L = 1.6, 145 mg/dl = 29.0

If you are converting between the two measurement systems, and this will be a long-term concern, you might need to create a table, or use some simple calculation.

20% will apply to whatever unit you are measurement unit you are using.

Here is dexcom documentation for 20/20 rule. 20 points under 80
20% over 80
(or mmol equivalent).
Most of the time you’ll probably using >80, so 20% applies.

From dexcom website.
If you’d like, you can calculate the 20 rule on your own. The Dexcom G6 reading must be within:

  • 20% of the meter value when the meter value is 80 mg/dL or higher
  • 20 mg/dL of the meter value when the meter value is under 80 mg/dL

Please note: the information listed here is applicable to Dexcom CGM users within the US only.

Full details


I honestly don’t care what numbers they say to calibrate at or how often. I want mine to be within 5 points ( .3 mmol) so I calibrate when it first starts or restarts, Then I try to wait a few hours to calibrate again. By the next morning I then fine tune it to be within 5 points.


That’s an amazing level of accuracy, Marie. I’m glad you mention that you are able to achieve this, otherwise I would never think that was possible. I think that even trying to do this would break the algorithm for me. Its so interesting. But, I had better accuracy on G4. I would not have thought changing models would make so much of a difference, either.

Personally I think Dexcom wants you to accept that 20% off is okay so you don’t want to try to replace a sensor that keeps being off. But I always calibrate at around 100. It will be off more when you at at " higher " numbers but I don’t care about that for my purposes.

I’ve calibrated mine when it’s been within 5 points, 7 points etc because I want mine to be within 5 points and I want it within 5 points over what I’m actually at, my preference is for it not to be under. Some take more work than others. But one thing I always do is consistently check it at about the same numbers and calibrate it around those numbers. That is around 100, if I check it at 150, I know it can be off by more. I am not afraid to screw it up as I can always restart them. But I haven’t had to once I learned to do the exact number 2 times, one right after the other and it takes that second number.

Be forewarned that if you calibrate a new sensor or a restarted sensor with my 2 numbers in a row, it doesn’t stop the adjustments of a new algorithm so you will still end up with a new sensor that in a couple of hours wants to raise your numbers and a restarted sensor that might lower your numbers as it thinks it needs to adjust.


So that suggests even if you calibrate it when its under 20% it is still ok! Thats good to know because when it gets over 10%, it really makes a difference in the values.

Also I’ve done a few calibrations. In the scenario where my sensor was higher than my meter, I find it overcompensates after I calibrate… so that it will end up with my sensor reading lower than my meter reading. Do you find yourself lying to the pump and punch in a number very slightly higher (so if i was 5.3 mmol, I would put in 5.4mmol) than your meter reading so that it doesn’t overshoot.

Hey Marie20, can I inquire with you about something that popped up in another post?
Wondering about your sensor placement and if sensor location might possibly be a contributing factor for some of us getting a lot of error.

Do you always put yours in the same place? Do you put it into your abdomen? Or, do you move it around?

@mohe0001 I always put them on my arm. I like the front the best but I rotate them and use the back of the arms too. I just try on the front of the arm to not put it right over a muscle. Plus I always restart as much as possible and I calibrate them as often as needed until I get the numbers I want. And I always calibrate it around 95-105 to make sure I consistently compare it around the same numbers. I expect it to be off more at 140 or 150.

I’m not afraid of messing them up as I can always restart one. But with double calibration that hasn’t been a problem.


Is there a way to tell where the muscle is?

@tedos…I can see my largest arm muscle, maybe not smaller ones, but I meant the larger one at the top of your arm if you crook your elbow with a fist pointed up you should be able to see and feel it?

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You can tell where the muscle is by flexing and feeling for the part that is jiggly. Go for that !

When you start a sensor with no code and it asks for calibration, the +/- 20% rule doesn’t apply here does it? Because my sensor seems to be pretty accurate with my meter reading when it asked me for a calibration. If I ignore it, it just keeps asking.