What the glucose ketone index is
The glucose ketone index (GKI) is one number that puts your blood glucose and your blood ketones side by side. It is the ratio of glucose to beta-hydroxybutyrate (BHB), the main ketone in your blood, with both measured in mmol/L. When glucose falls and ketones rise, the GKI drops. When you eat more carbohydrate, glucose goes up, ketones fall, and the GKI climbs.
It comes from a 2015 paper by Meidenbauer, Mukherjee, and Seyfried at Boston College, who built a simple calculator to track ketogenic metabolic therapy in people and mice with brain tumors. Their point was practical: glucose and ketones both swing through the day, and following a single ratio is easier than juggling two numbers. That origin matters. The GKI was designed for supervised therapy research, and the targets in that work were never meant as goals for everyone on a keto diet.
How to calculate it by hand
GKI = glucose (mmol/L) ÷ BHB (mmol/L)
glucose mmol/L = glucose mg/dL ÷ 18.0
BHB mmol/L = BHB mg/dL ÷ 10.41
Glucose-to-ketone ratio = glucose (mg/dL) ÷ BHB (mmol/L) = GKI x 18
A worked example: a glucose of 90 mg/dL is 5.0 mmol/L. With ketones at 1.5 mmol/L, the GKI is 5.0 ÷ 1.5 = 3.33. The 18.0 factor comes from glucose's molar mass of about 180 g/mol (the original paper uses 180.16, a difference of less than 0.1%). The 10.41 factor comes from BHB's molar mass of 104.1 g/mol, and only matters if your ketone meter reports in mg/dL.
Reading your number
There is no clinical standard for GKI bands. The most widely shared chart comes from Keto-Mojo, a company that makes a combined glucose and ketone meter, which presents its ranges as educational material:
| GKI | Keto-Mojo's description |
|---|---|
| 9 or higher | Not in meaningful ketosis |
| 6 to 9 | Low level of ketosis |
| 3 to 6 | Moderate level of ketosis |
| Under 3 | High, therapeutic level (usually pursued for medical conditions, with supervision) |
Meidenbauer and colleagues described values approaching 1.0 as potentially most therapeutic in their brain-cancer context. Reaching that level usually takes a strict therapeutic diet, often with calorie restriction, and belongs under medical supervision. For someone using keto for weight or general health, the trend in your own readings, taken under the same conditions, is more useful than chasing the lowest possible number.
The glucose-to-ketone ratio (the "Dr. Boz ratio")
Some clinicians skip the glucose conversion and divide glucose in mg/dL straight by ketones in mmol/L. Dr. Annette Bosworth popularized this as the "Dr. Boz ratio". It carries exactly the same information as the GKI, multiplied by 18: a GKI of 3.33 is a ratio of 60, and a GKI of 1 is a ratio of 18. The calculator shows both so you can compare with whichever one you have seen quoted. Targets commonly circulated for the ratio, such as staying under 80, come from clinical practice and popular books rather than peer-reviewed studies, so this tool does not grade it.
Blood ketone ranges
The ketone reading on its own still matters, and the calculator bands it separately. Nutritional ketosis is usually described as 0.5 to 3 mmol/L of BHB. Below 0.5 is common in the first days of a keto diet or after a higher-carb meal. Above 3 is not a goal for weight loss or general health, though it can happen during a longer fast. Readings above 5 mmol/L, especially with high glucose or when you feel unwell, are a reason to seek medical care.
Nutritional ketosis is not ketoacidosis. In diabetic ketoacidosis, ketones climb far higher and the blood becomes acidic, usually because there is not enough insulin. It is a risk mainly for people with type 1 diabetes and people who take SGLT2 inhibitors (such as empagliflozin, dapagliflozin, or canagliflozin), where it can occur even with near-normal glucose. If either applies to you, follow the ketone plan your care team gave you, and talk to them before starting a ketogenic diet.
Blood, breath, and urine: why only blood works here
Blood meters (BHB)
A finger-prick blood ketone meter measures beta-hydroxybutyrate directly, in the same units the GKI uses. It is the only home method the GKI can be calculated from. Combined meters that read both glucose and ketones from separate strips make it easier to test the two together.
Breath meters (acetone)
Breath analyzers measure acetone, a ketone you exhale. Breath acetone tends to rise with fat burning, but it is affected by diet, exercise, and the device itself, and it is a different molecule from BHB. There is no valid formula to turn a breath reading into a blood BHB number, so it cannot go into a GKI.
Urine strips (acetoacetate)
Urine strips detect acetoacetate that your kidneys spill into urine. The color depends on how much you drink, the time of day, and how keto-adapted you are, and strips often fade after the first weeks even when you are still in ketosis. They are a cheap yes-or-no check. They cannot be converted into a blood value. Our guide on how to test for ketosis compares the three methods in more detail.
What the GKI cannot tell you
Home meters have a margin of error for both glucose and ketones, and because the GKI divides one by the other, small errors add up, especially when ketones are low. A single reading after a meal, a hard workout, or a bad night's sleep can look very different from your usual pattern. Exogenous ketone drinks and supplements raise blood BHB for a few hours, which lowers the GKI, but that reflects the supplement rather than your own ketone production.
Most of all, the GKI is a tracking number, not a diagnosis. It is not a tool for diagnosing or managing diabetes, and it does not show whether a diet is working for your health overall. For that, lab markers such as triglycerides, HDL, fasting insulin, and HbA1c say more; the Metabolic Health Calculator turns them into the ratios researchers use. If you are using ketosis as part of treatment for a medical condition, the targets and the testing schedule are decisions for you and your clinician.