GKI & Dr. Boz ratio calculator

What the Glucose Ketone Index tells you

Looking at glucose or ketones alone can be misleading. Your glucose can sit in a normal range even when you're fully fat-adapted, and your ketones can be elevated while your glucose is still high — a mixed-fuel state. The GKI folds both sides into one number, so you see the actual metabolic environment your cells are in.

GKI = glucose (mmol/L) ÷ ketones (mmol/L)

If your meter reads glucose in mg/dL, divide by 18 to convert to mmol/L first — the calculator above does this for you automatically.

Where the GKI comes from

The index was introduced by Dr. Thomas Seyfried and colleagues at Boston College. In their 2015 paper in Nutrition & Metabolism, they proposed it as a way to track the effect of ketogenic metabolic therapy — originally in the context of managing brain cancer, where lowering glucose relative to ketones matters. The idea that carried over to everyday keto and fasting is simple: glucose and ketones aren't just two separate numbers — their ratio is what defines the metabolic environment your cells actually run in.

GKI zones

Zone	GKI	What it means
Therapeutic	Under 1	Deep ketosis — the level studied in Seyfried's clinical research on metabolic therapy.
Moderate ketosis	1 – 3	Strong ketosis with well-controlled glucose.
Mild ketosis	3 – 6	Light ketosis, common early in a fast or low-carb diet.
Out of ketosis	Over 6	Minimal ketosis — your body is running mainly on glucose.

The under-1 therapeutic threshold comes from Meidenbauer, Mukherjee & Seyfried (2015), Nutrition & Metabolism. The other zones are practical guidelines widely used in the keto community, not clinical cut-offs.

What the Dr. Boz ratio tells you

Dr. Boz built her ratio for people whose meters read glucose in mg/dL — most of the U.S. There's no unit conversion to trip over: you take the glucose number and divide it by the ketone number. She uses it especially around fasting, as a quick read on how deep a fast has taken you.

Dr. Boz ratio = glucose (mg/dL) ÷ ketones (mmol/L)

Dr. Boz ratio zones

Zone	Ratio	What Dr. Boz suggests it means
Deep ketosis	Under 40	Deeper ketosis that she associates with autophagy and cellular repair during fasting.
Moderate ketosis	40 – 80	A solid range for general health and weight management.
Glucose-burning	Over 80	Still running mostly on glucose — more fasting time or fewer carbs may help.

Zones per Dr. Boz (Annette Bosworth, MD), bozmd.com. These are her general guidelines, not medical advice.

Why people track a metabolic ratio

Whether you use the GKI or the Dr. Boz ratio, one blended number is more useful than glucose or ketones on their own. Here's what it actually unlocks.

It answers "is my fast actually working?"

Plenty of people hit 16, 24, even 48 hours fasted and still wonder whether they're truly in deep ketosis or just coasting. Glucose alone won't tell you — it can sit in a normal range even when you've fully switched to fat-burning. Ketones alone won't either, because high glucose next to high ketones is still a mixed-fuel state. The ratio captures both sides in a single number, so you're not guessing.

It reveals your personal carb threshold

Everyone's metabolism is different. Some people can eat 40g of carbs and hold a GKI under 6 (a Dr. Boz ratio under 80); others spike out of ketosis at 20g. Test before and after meals for a few days and you can map exactly where your line sits — no generic macro calculator required.

It tracks your metabolic flexibility over time

As you become more fat-adapted, you'll notice your ratio drops faster after meals and stays lower during fasts. Watching that trend over weeks and months is one of the clearest ways to see whether your metabolic flexibility is genuinely improving — not just how you feel on a given day.

It helps you time your refeed

For protocols like OMAD (one meal a day) or 5:2, checking your ratio before you break a fast lets you make a smarter first-meal choice. If your number is borderline, you might stretch the fast another hour or two rather than break it on something that spikes you straight out of ketosis.

What you need to calculate either ratio

Both ratios use the same two readings, taken at roughly the same time:

Blood glucose — from any standard glucose meter. A continuous glucose monitor works too, though it can lag a finger-prick reading by 10–15 minutes.

Blood ketones — from a meter that reads blood beta-hydroxybutyrate (BHB). Urine strips (which measure acetoacetate) and breath meters (which measure acetone) aren't accurate enough for these ratios — you want blood BHB.

For the most consistent numbers, test first thing in the morning before eating or drinking anything but water. That's your fasted baseline. New to testing? Here's how to test your ketones, step by step.

Glucose and ketone reference ranges

The calculator flags where each reading lands as you type. Here's the full picture for both inputs.

Blood glucose (mg/dL)

Zone	Range	What it means
Normal	Under 100	Typical fasting blood sugar.
Elevated	100 – 125	Above the usual fasting range — worth watching in context.
High	126 – 199	Well above a normal fasting reading.
Very high	200+	Substantially elevated.

General reference ranges for context only — not a diagnosis. If your glucose readings concern you, talk to your doctor.

Blood ketones — BHB (mmol/L)

Zone	Range	What it means
Trace	Under 0.5	Little to no ketosis — mostly glucose for fuel.
Light ketosis	0.5 – 0.9	The shift into fat-burning has started.
Nutritional ketosis	1.0 – 2.9	The zone most people aim for on keto.
Deep ketosis	3.0+	Often seen with extended fasting or strict carb limits.

Common questions

Which number should I track — GKI or Dr. Boz?

Whichever clicks for you. They describe the same thing on different scales. If you think in mg/dL, the Dr. Boz ratio is less math. If you follow the research or use mmol/L, GKI is the standard. Many people just pick one and stick with it so their trend stays consistent.

Why does my ratio look "high" even though my glucose is normal?

Both ratios are glucose divided by ketones. If your ketones are very low, the ratio climbs no matter how normal your glucose is — which simply means you're running mostly on glucose at that moment. Perfectly normal for someone eating a standard diet.

What's a good number to aim for?

It depends on your goal. For general wellness and steady fat-burning, a GKI of 3–6 or a Dr. Boz ratio of 40–80 is a common target. Deeper ketosis (GKI under 3, Dr. Boz under 40) is what some people chase for fasting and therapeutic goals. There's no universal "perfect" number — your optimal is personal.

How often should I test?

Once or twice a day is plenty for most people. If you're dialing in your carb tolerance or experimenting with fasting lengths, test more often for a week or two to build your personal data set, then ease back to maintenance testing.