Blood Glucose Converter

What this tool does

A lab report says 5.5 mmol/L while the meter at home reads 99 mg/dL. They look nothing alike, yet they describe the same concentration. This tool handles exactly that conversion in both directions using the factor 18.0182, so filling one field produces the other immediately without digging out the formula.

It also maps HbA1c to estimated average glucose using eAG = 28.7 × HbA1c − 46.7 in mg/dL, then converts that estimate back into mmol/L. An HbA1c of 7.0 percent corresponds to roughly 154 mg/dL, or about 8.6 mmol/L. Low, usual and elevated ranges are marked so a number comes with context instead of standing alone.

Direction is chosen from a dropdown and neither input is pre-filled. Converting without picking a direction produces a prompt rather than treating an empty field as zero and printing 0.0. The example button fills both direction and value, so one click yields a complete result.

The factor 18.0182 comes from the molar mass of glucose and is the conventional bridge between millimoles per litre and milligrams per decilitre. Multiplying mmol/L by that factor gives mg/dL; dividing mg/dL by it goes the other way. Because a meter and a lab report usually round differently, a converted value can differ by a tenth from a number printed elsewhere, and that is a rounding artefact rather than a disagreement between instruments. The HbA1c field uses eAG = 28.7 × HbA1c − 46.7 in mg/dL, then converts that estimate into mmol/L so both figures sit side by side. Estimated average glucose describes a period of roughly three months and should never be compared directly with a single finger-prick reading taken after a meal. Range labels are reference bands for orientation only; a clinician reads a glucose number together with timing, whether the sample was fasting, and the rest of a person's history. The direction dropdown is intentionally empty on load, and converting without choosing it raises a prompt instead of treating the blank as zero. Invalid text in the numeric field is rejected and the previous warning clears once a valid value is converted successfully. No values are saved or transmitted, so the page is a conversion aid rather than a log; write down anything you need to bring to an appointment.

Key features

• Two-way conversion: Switch between mmol/L and mg/dL in either direction with the fixed factor 18.0182, rounded to one decimal place.
• HbA1c estimate: Enter glycated haemoglobin to get estimated average glucose in both units at once.
• Range guidance: Common low, usual and elevated bands are labelled with both colour and text.
• Direction required: The direction dropdown starts empty; converting without it prompts instead of returning zero or NaN.
• Working example: The example button fills direction and value together so the result appears immediately.
• Errors clear themselves: After correcting an input and reconverting, the previous red warning disappears.

How to use it

1. Choose direction: Select mmol/L to mg/dL or the reverse from the dropdown.
2. Enter a number: Type the glucose value, for example 5.5 or 99, without any unit text.
3. Press Convert: The result area shows the converted value and its range label.
4. Check HbA1c: For a longer-term view, enter a percentage in the HbA1c field to see estimated average glucose.
5. Clear: The clear button returns direction, inputs and results to an empty state together.

Things to keep in mind

• Not a diagnosis: Reference bands only help interpret a number; a clinician must judge it against fasting or post-meal timing.
• Numbers only: Unit text pasted into the field is rejected as invalid and must be retyped as a plain number.
• Conventional factor: 18.0182 is the standard molar-mass conversion; individual meters may round slightly differently.
• eAG is an estimate: Estimated average glucose is not the same thing as a single finger-prick reading.
• Nothing is stored: Inputs live on the current page and vanish on refresh, so write down anything you need to keep.