Blood Sugar Units Explained: mg/dL, mmol/L, HbA1c and eAG

mg/dL and mmol/L are the same blood glucose written on two scales: divide mg/dL by 18.0182 to get mmol/L, or multiply mmol/L by 18.0182 to go back. HbA1c — a longer-term measure — has its own pair of scales (percent and mmol/mol) plus an “estimated average glucose” that maps it back onto the familiar meter reading. This guide connects all four so a number in one system stops being a mystery. Convert instantly with the Blood Sugar Converter and the HbA1c Converter — both run locally in your browser.

These tools and this article explain unit conversions only. They are not medical advice and can’t tell you whether a value is high, low or normal for you — that depends on your circumstances and is a question for a healthcare professional.

Glucose: mg/dL ↔ mmol/L

A glucose reading is a snapshot — your blood sugar right now, from a meter or lab. Two conventions report it:

• mg/dL (milligrams per decilitre) — a measure of mass per volume. Used in the US, Germany, France and Japan.
• mmol/L (millimoles per litre) — a measure of number of molecules per volume. Used in the UK, Canada, Australia and most of the world.

They differ by a single fixed factor:

mmol/L = mg/dL ÷ 18.0182 · mg/dL = mmol/L × 18.0182

That 18.0182 isn’t arbitrary. It comes from glucose’s molar mass — roughly 180 g/mol — combined with the decilitre-to-litre step (a factor of 10). Two unit differences collapse into one number, so the conversion is a clean, reversible constant with no rounding baked in. Some references round it to a flat 18, which shifts a reading by well under 1% — fine for a mental estimate, but the tools use the full 18.0182 so a round-trip lands back where it started.

Worked example. A UK lab reports a fasting glucose of 5.4 mmol/L. Multiply by 18.0182 → 97 mg/dL — squarely in the normal fasting range on the US scale. Going the other way, a US reading of 126 mg/dL ÷ 18.0182 = 7.0 mmol/L, the number most guidelines cite as the fasting threshold for diabetes. Same blood, two vocabularies.

mg/dL	mmol/L
70	3.9
100	5.6
126	7.0
140	7.8
180	10.0
200	11.1

SNAPSHOT · glucose right now mg/dL US, DE, FR, JP

mmol/L UK, CA, AU, world

↔ ÷ 18.0182 · × 18.0182

AVERAGE · last 2–3 months HbA1c % NGSP / DCCT

mmol/mol IFCC eAG avg glucose (mg/dL · mmol/L)

↔ → IFCC = 10.929 × (% − 2.15) eAG mg/dL = 28.7 × % − 46.7 (ADAG, 2008)

HbA1c: a different measurement entirely

HbA1c isn’t a snapshot. It measures the fraction of your haemoglobin that has become glycated — bonded with glucose — which builds up over the ~2–3 month lifespan of red blood cells. So it reflects your average glucose over months, not this morning’s reading. And like glucose, it’s reported on two scales:

• NGSP / DCCT (%) — the older percentage scale, aligned to the Diabetes Control and Complications Trial. A value like “7%”.
• IFCC (mmol/mol) — the newer international standard: millimoles of HbA1c per mole of total haemoglobin. A value like “53 mmol/mol”.

The two are linked by the IFCC–NGSP master equation:

IFCC (mmol/mol) = 10.929 × (NGSP% − 2.15)

So 7% → 53 mmol/mol, and 8% → 64 mmol/mol. Since around 2011 many labs report both side by side, which is exactly when people start needing to convert.

eAG: putting HbA1c back on the meter scale

An HbA1c percentage is hard to picture next to your daily readings. The estimated average glucose (eAG) fixes that. From the ADAG study (Nathan et al., Diabetes Care, 2008), which correlated HbA1c with continuous glucose monitoring:

eAG (mg/dL) = 28.7 × HbA1c% − 46.7

Then divide by 18.0182 for mmol/L. So an HbA1c of 7% ≈ 154 mg/dL (8.6 mmol/L) average glucose.

HbA1c %	IFCC mmol/mol	eAG mg/dL	eAG mmol/L
6.0	42	126	7.0
6.5	48	140	7.8
7.0	53	154	8.6
7.5	58	169	9.4
8.0	64	183	10.2

eAG is a population average: two people with the same HbA1c can have somewhat different true average glucose because red-cell turnover varies. Treat it as a helpful translation, not a personal guarantee.

Reference ranges for context

Conversions only tell you the number, not what it signifies. For orientation, the table below shows the broad categories the American Diabetes Association uses, on every scale at once. These are general diagnostic thresholds — a clinician interprets them alongside your history, symptoms and repeat testing, and some conditions (pregnancy, anaemia, certain haemoglobin variants) shift how the numbers behave.

Category	Fasting glucose (mg/dL)	Fasting glucose (mmol/L)	HbA1c (%)	HbA1c (mmol/mol)
Normal	below 100	below 5.6	below 5.7	below 39
Prediabetes	100–125	5.6–6.9	5.7–6.4	39–46
Diabetes range	126 or above	7.0 or above	6.5 or above	48 or above

The point of lining the scales up like this is that a single result — say 6.5% — is simultaneously 48 mmol/mol on the IFCC scale and an eAG of about 140 mg/dL (7.8 mmol/L). None of those are different findings; they’re the same fact in four dialects.

Where the conversions trip people up

A few recurring snags are worth naming:

• Mixing up the two “mmol” units. Glucose is reported in mmol/L; HbA1c on the IFCC scale is mmol/mol. They look similar but measure completely different things — never convert one into the other directly.
• Applying 18.0182 to HbA1c. The glucose factor only bridges mg/dL and mmol/L. To move an HbA1c percentage onto a glucose scale you must go through eAG first, then apply 18.0182 if you want mmol/L.
• Over-reading small differences. Because HbA1c reflects a months-long average, a change from 6.9% to 7.0% is within normal measurement noise, not a meaningful jump. eAG inherits that same fuzziness.
• Rounding drift. Rounding mg/dL to a whole number before converting, then rounding again, can shift the last digit. Converting from the raw value in one step — which the calculators do — avoids it.

Putting it together

• A glucose reading is now; convert mg/dL ↔ mmol/L with ÷ or × 18.0182.
• HbA1c is a 2–3 month average; convert % ↔ mmol/mol with IFCC = 10.929 × (% − 2.15).
• eAG bridges the two, turning an HbA1c into an average meter reading with 28.7 × % − 46.7.

Do the arithmetic instantly and privately with the Blood Sugar Converter and HbA1c Converter — and remember these convert units, they don’t interpret them. For what your numbers mean, talk to your clinician.