Gestational Diabetes Glucose Threshold Calculator
Oral glucose tolerance test results are read against time-point thresholds that differ by diagnostic protocol. This calculator compares one reading against the threshold you enter, in mg/dL, and flags whether the value meets or exceeds it. It also converts your reading exactly to mmol/L using the standard glucose factor of 18.0182. Because protocols and labs differ, the threshold is yours to enter from your report. It is a unit-conversion and comparison aid only, not a diagnosis: gestational diabetes is diagnosed by your clinician using the full protocol.
Comparison and conversion formula
mmol/L = mg/dL / 18.0182
Status = met or exceeded if reading >= threshold, otherwise below
Difference = reading - threshold
The 18.0182 factor is the exact molar conversion for glucose. The threshold you enter should match the time point and protocol used by your laboratory.
Glucose testing context
- Thresholds differ at fasting, one hour, two hours, and three hours.
- Different protocols use different cut-offs; enter the one your lab used.
- The mg/dL to mmol/L conversion factor for glucose is 18.0182.
- Some protocols diagnose on one abnormal value, others require two.
- This tool converts and compares only and is not medical advice.
Glucose threshold: frequently asked questions
What does this calculator do?
It compares one oral glucose tolerance test reading against the diagnostic threshold for that time point. It also converts between milligrams per deciliter (mg/dL) and millimoles per liter (mmol/L) exactly, and flags whether your value meets or exceeds the threshold. Because thresholds differ by protocol, you enter the threshold yourself.
Why are the thresholds user-entered?
Different diagnostic protocols use different cut-offs at fasting, one hour, two hours, and three hours, and laboratories report against their chosen protocol. Rather than assume one set, this calculator asks you to enter the exact threshold from your test report or clinician, so the comparison matches your lab.
How do you convert mg/dL to mmol/L for glucose?
For glucose, millimoles per liter equals milligrams per deciliter divided by 18.0182, the molar mass conversion factor for glucose. To go the other way, multiply mmol/L by 18.0182. This conversion is exact and is the standard factor used worldwide.
What does meeting or exceeding a threshold mean?
In most gestational diabetes protocols a value at or above the time-point threshold is considered abnormal for that point. Some protocols diagnose gestational diabetes on a single abnormal value and others require two. This tool flags one value against one threshold; diagnosis rests with your clinician using the full protocol.
Is this calculator medical advice?
No. It converts units and compares one number to a threshold you supply. It does not diagnose gestational diabetes or replace laboratory interpretation. Always rely on your obstetric provider and laboratory for diagnosis and management.
Official sources
- U.S. Centers for Disease Control and Prevention: Diabetes.
- U.S. National Library of Medicine, MedlinePlus: glucose tolerance test.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.