Simplified Carb Ratio and Sensitivity Ratio

You would think after being on the pump for years I would have this figured out, no I do not.

I have too many lows and am not sure what to adjust. when I put in my carbs the amount of insulin suggested is more than I need on a regular basis.

My carb Ratio is 1:20
My correction factor is 1:17
My basal is 0.3, 0.2

I am hoping to get a simple explanation of these factors.

All help appreciated.

Thank you

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Below link is a good site to learn about pumping, with tips on tweaking your settings. If interested, they will set up appointment to give personalized advice for a fee.

The book “Think Like a Pancreas” is great, and the author runs the site above (Gary Schiener), so some of the same info is in that book.

“Pumping Insulin” is also good book, by
John Walsh.

Carb ratio says if you eat 20 carbs, you need 1 unit of insulin

Correction factor means 1 unit of insulin will decrease your BG by 17.

Basal of .3 .2 means the rate of insulin per hour that is delivered for the time block assigned to.

However, these numbers are approximations. A given time they vary, since many other factors influence your BGs, such as exercise, stress, etc. So if you just exercised, and then eat, your bg may drop if you do 1 unit for 20 carbs.
And during/after exercise, your basal rate may cause your bg to drop.

So having CGMS or frequent bg testing is best way to use pump and make corrections based on bg trend up, down or flat.
If you have CGMS, Sugar Surfing is a great book and website.

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A carb ratio is simply the number of grams of dietary carbohydrates that one unit of insulin can metabolize while holding your glucose within a desired range. Your ratio of 1:20 means that 1 unit of insulin covers 20 grams of dietary carbs. Also known as carb factor.

A correction factor shows how many mg/dL one unit of insulin can drop or correct an out-of-range high blood glucose. Your correction factor of 1:17 indicates that one unit of insulin will drop your high glucose level by 17 mg/dL. Also known as Insulin Sensitivity Factor or ISF.

A basal rate (usually attributed to insulin pump management) is the amount of insulin units per hour delivered. The basal rate is intended to metabolize the steady drip of glycogen (glucose) typically released by the liver – nothing more, nothing less.

An optimized basal rate will keep your glucose levels steady when not eating. Basal rate needs often fluctuate over the day and are customized for each person. Many of us need more basal insulin in the early morning hours and less basal insulin in the late afternoon hours. Everyone is different in their basal needs and these needs do change.

All three of these settings may need to change over time. Your job is to detect that changing need and adjust your settings to counteract that change and leave your glucose in a desired range. A good example of this is often reported related to a women’s monthly cycle.

Wearing a CGM (continuous glucose monitor) and paying attention to its data-stream can educate you about your custom needs.


Did you choose these settings or did someone else (who?) pick them for you? When did this happen? (How long have you been using these settings?)

Are you currently using a CGM or just a BG meter?

What support have you gotten from your medical team for using your pump?

I’ll throw it out there… Both your carb ratio and basal suggest you’re still pretty sensitive to insulin. Everyone’s needs are different, but both those values deliver less insulin than “average”.

Yet… Your correction factor is really low in comparison! Just for comparison, I’m on the opposite end of the spectrum. I’m fairly insulin resistant and need way more insulin than my petite size would indicate. My correction factor is 1:46. I need roughly 1 unit of insulin to drop me 46 points, even while battling all my insulin resistance. You’re taking a full unit of insulin to drop you just 17 points! That doesn’t correlate with your sensitive basal and I:c ratio settings.

Edit: After I typed this, I realized the “17” in question might indicate mmol rather than the mg/dl which dominates in the US. I guess the 17 might actually correlate after all if you use the mmol system. I’m going to let my comment stand, though, in case you are actually in the US.

Since there’s a factor of 18 between mg/dL and mmol/L a 17 mmol/L would equate to a 1:306 mg/dL correction factor, not likely.

@Nan – please confirm what units your correction factor uses. I know Canada, Australia, and most of Europe uses mmol/L.

Well what you are telling me is what I understand.
But, even when I change my basal rate, when I put in my Carbs; n my pump gives too much insulin. That is why I am questioning my correction and sensitivity factor.

Nan, you need to work with your diabetes team and do some work and testing to get the best basal Bolus levels. You’ll first use the calculation based on your weight to figure your total daily insulin required. Then from that you’ll use a percentage for basal and the rest as bolus. Mine is 60 percent bolus and 40 percent basal. This is for a confirmed T1D using only insulin for treatment. For T2D, it gets far more complicated. From you ratios I’d just guess your basals too high but you you absolutely need to work with your doctor.

Can you give an example?

You should test your basal rate while fasting. Changing basal rate should not affect the food bolus calculation. But it will impact total insulin in your system.

But pump should show IOB as just the food bolus amount (including any +/- adjustment based on the sensitivity factor and target bg).

But if basal setting is off, it can lead to incorrect assessment of your other settings.

Add on that many people have different basal patterns based on time of month (hormones), exercise, stress, etc.

Are you a new pumper, or have other things changed recently with impact of COVID?

Here is example instructions.for basal testing. Need to get this right first, in order to get other setting right.

Getting the books I mentioned before will provide details like this.

Or as mentioned by others, work with your medical team.

No I am not a new diabetic, nor am I new to the pump. I am a Type 1.

We moved from Texas to Louisiana right before Hurricane Laura and then Hurricane Delta hit. We were immediately evacuated. Then again for Delta. Weeks of stress, sitting in hotel rooms, and poor meals have taken a toll on my control.

I do not have a new ENDO and many of our facilities are not open. So for this period of time I am on my own.

I am just now able to get my diet back under control. In addition living in hotels and a poor diet have caused a significant weight gain. This is new to me and I am working to rectify it.

I have a tendency toward low blood sugar and feel I am on a roller coaster that I want off. I am not going to have access to the same type of care that I have always had. We are in a more rural area and until we can get to a better location I am on my own. I am 74 years old.

My basal rates are pretty low at 0.2 and 0.3 respectively. That is why I asked about adjusting the carb ratio or the correction factor. I can’t remember if you are running frequent lows; do you increased/decrease the carb factor, and the same question for the correction factor.

Prior to the move and hurricanes my control was excellent.

Thanks for the advice.

For what it’s worth, rather than answering directly, here is a link to another post where I attempted to answer this question. I hope it helps. If not someone else will no doubt also jump in.

I don’t recall if you told us which pump you are using. If you are using one of the newer pumps which automatically change your basil settings and/or deliver correction boluses that could be another reason why you are having problems.

So, which pump are you using?

Thank you John.

Tandem T-Slim

Frequent lows -Yes

Don’t know which way to adjust Carb Ratio or Correction to get LESS insulin.

Again, thanks


To simplify, your statement says you are going low after blousing for your calculated carb intake. If you make the carb ratio larger (e.g. 25 instead of 20) then you will take less insulin for the food you are eating, so that would be the first change to try. Same is true for correction ratio: if you are getting too much insulin for your correction boluses, then test with a larger ratio (e.g. 25 instead of 17) to bolus less correction insulin.

The problem is that simplifying is not usually the best approach. Your real issue could be something altogether different: your basal rate, your carb counting skills, prebolus delay, etc., etc. So make that adjustment then see what is next.

Does your pump support Tandem’s Control-IQ (CIQ)? If so, are you using it? If you are using CIQ then the pump is changing your basal rates and could also be delivering correction boluses. Are you using Dexcom CGM with your pump?

Will do. Thank you.

Short answers: the ratio is typically written as gms of carbs per or over 1 unit of insulin. If my carb ratio is 7/1 but I’m experiencing lows I’d try raising the carb number to 8 gms of carbs to one unit of insulin. Correction factor is written such that 1 unit of insulin brings your bg down 70 points. If you’re dropping low, raise it to 80 points. That means each unit of insulin brings bg down by 80 points so you will get less correction bolus. Those numbers are for example only.

Have you tried using the exercise function or sleep function on your TSlim?
Also, you can find proper carb counting for fast food since your diet and meals have been so disrupted. You could try finding Diabetes Certified Nurse for refills until you find an Endo. He/she can prescribe whatever you need for diabetes care.

you could try fasting for several hours (perhaps overnight). measure glucose before and afterwards. if it increased, then decrease the basal rate; if it decreased, then increase the basal rate. you could use your correction factor and the length of time to calculate how much to increase or decrease. : BG change / CF = amount of insulin to increase or decrease. basal rate change would be BG change / (CF * time).