Lab Values Converter (US ↔ SI Units)

Lab unit conversion in brief

Blood test results are reported in two main unit systems. US conventional units express most results as a mass per volume – milligrams per decilitre (mg/dL), nanograms per millilitre (ng/mL) or micrograms per decilitre (µg/dL). SI units (from the French *Système international d'unités*), used in the UK, Europe, Australia, Canada and most of the world, express most results as an amount of substance per volume – millimoles per litre (mmol/L), nanomoles per litre (nmol/L) or picomoles per litre (pmol/L).

The converter above handles 29 common tests. Choose the test, enter a value in either unit, and the result appears instantly. Each test also has its own page with a conversion chart, typical reference ranges, an explanation of what the result means and sources.

The key point is that there is no single conversion factor. Converting mg/dL to mmol/L depends on the molar mass of the substance being measured. Glucose uses a factor of about 0.0555, cholesterol 0.0259, triglycerides 0.0113 and creatinine 88.4 (to µmol/L). Using the wrong factor is one of the most common sources of error when people compare results from different countries.

Why two systems exist

In 1977, the World Health Assembly recommended that medicine adopt SI units, and international bodies such as the International Federation of Clinical Chemistry (IFCC) endorsed them. Most countries switched during the 1970s and 1980s. The main argument was scientific: chemical reactions and physiology work in terms of numbers of molecules, not their weight, so molar units make relationships clearer. For example, in SI units, calculated osmolality is simply 2 × sodium + glucose + urea.

The United States began a transition in the 1980s – the *Journal of the American Medical Association* announced in 1986 that it would report SI units – but US laboratories and clinicians largely kept conventional units, partly because of concerns that changing familiar numbers could lead to dangerous errors. Today, US laboratories mostly report conventional units, while many US journals publish both. Canada converted fully to SI units. As a result, anyone moving between countries, reading international research or getting tests abroad needs to convert.

SI prefixes used in lab reports

Lab results span an enormous range of concentrations – from sodium at around 140 mmol/L to some hormones at a few picomoles per litre, a difference of roughly a hundred billion times. Prefixes keep the numbers manageable:

When converting, a mistake of one prefix step – for example, reading nmol/L as pmol/L – changes the result a thousand-fold. Always check the prefix as well as the base unit.

How conversion works

For substances measured in mass units, the conversion uses the molar mass (in g/mol):

• mmol/L = mg/dL × 10 ÷ molar mass
• mg/dL = mmol/L × molar mass ÷ 10

The factor of 10 converts decilitres to litres. For glucose (molar mass 180.16 g/mol), mmol/L = mg/dL × 10 ÷ 180.16 = mg/dL × 0.0555. That is why the often-quoted shortcut is "divide by 18".

For smaller units, the same principle applies with different powers of ten. Vitamin D (25-hydroxyvitamin D, molar mass 400.6 g/mol) converts from ng/mL to nmol/L by multiplying by 2.496. Testosterone (288.4 g/mol) converts from ng/dL to nmol/L by multiplying by 0.0347.

Worked examples

• Glucose 126 mg/dL × 0.0555 = 7.0 mmol/L – the fasting diagnostic threshold for diabetes.
• Total cholesterol 200 mg/dL × 0.0259 = 5.17 mmol/L.
• Triglycerides 150 mg/dL × 0.0113 = 1.69 mmol/L.
• Creatinine 1.0 mg/dL × 88.4 = 88 µmol/L.
• Vitamin D 30 ng/mL × 2.496 = 75 nmol/L.
• Testosterone 500 ng/dL × 0.0347 = 17.3 nmol/L.
• Ferritin 50 ng/mL – reported as µg/L in most SI labs, which is numerically identical (50 µg/L).

Units that do not change

Some results are numerically the same in both systems, or change only by a factor of ten:

• ng/mL = µg/L (ferritin, PSA, vitamin D in some labs)
• pg/mL = ng/L (vitamin B12 in some labs, BNP)
• g/dL × 10 = g/L (haemoglobin, albumin, total protein)
• mEq/L = mmol/L for monovalent ions such as sodium, potassium, chloride and bicarbonate
• U/L for enzymes such as ALT, AST, ALP and GGT is used in both systems in most countries

Conversion factors for common tests

All factors convert US conventional → SI. To go the other way, divide by the factor.

Ferritin is usually reported in µg/L in SI laboratories rather than pmol/L; the pmol/L factor is included for completeness.

Common pitfalls

Cholesterol and triglycerides use different factors

Both are measured in mg/dL in the US, but cholesterol has a molar mass of about 387 g/mol while triglycerides are converted using a nominal molar mass of about 885 g/mol (based on triolein). Using the cholesterol factor for triglycerides overestimates them by more than double.

BUN is not urea

US laboratories report blood urea nitrogen (BUN) – only the nitrogen part of the urea molecule. Most other countries report urea. A BUN of 14 mg/dL equals a urea of 5.0 mmol/L, or 30 mg/dL of urea. Mixing them up leads to large errors; see our BUN to urea converter.

Phosphate versus phosphorus

US reports often say "phosphorus" but measure inorganic phosphate, expressed as the mass of phosphorus. The factor 0.3229 uses the atomic mass of phosphorus (30.97). The result in mmol/L is the same whichever name is used.

Hormones measured in international units

Some hormones – insulin, prolactin, TSH, LH and FSH – are measured against international reference preparations and reported in international units (IU or mIU). Converting between IU and mass requires a factor specific to the reference standard, and different assays may use different standards. For insulin, the conventional factor of 6 (1 µIU/mL = 6 pmol/L) is standard, though some argue for a factor closer to 6.945. For prolactin, 1 ng/mL ≈ 21.2 mIU/L under the WHO third international standard.

HbA1c has its own units

HbA1c is reported as a percentage (NGSP/DCCT) in the US and as mmol/mol (IFCC) elsewhere. The relationship is not a simple multiplication; it follows a master equation. Use our A1C calculator and HbA1c mmol/mol to percent converter.

"mcg" and "µg"

Both mean micrograms. "mcg" is often used to avoid confusion of µ with m (milli). An error between them would be a thousand-fold.

Rounding

Converted values should be rounded sensibly. A glucose of 5.5 mmol/L converts to 99.1 mg/dL; reporting it as "99" is appropriate, but rounding intermediate steps in multi-step calculations can introduce errors. The converter keeps full precision internally and rounds only the displayed result.

Reading a foreign lab report: an example

Suppose you live in the US and receive results from a hospital in the UK showing glucose 6.4 mmol/L (fasting), total cholesterol 5.8 mmol/L, HDL 1.2 mmol/L, triglycerides 2.1 mmol/L, creatinine 95 µmol/L, urea 6.5 mmol/L and vitamin D 42 nmol/L. Converted to US units:

• Glucose: 6.4 ÷ 0.0555 = 115 mg/dL – in the prediabetes fasting range (100–125 mg/dL).
• Total cholesterol: 5.8 ÷ 0.0259 = 224 mg/dL – borderline high.
• HDL: 1.2 ÷ 0.0259 = 46 mg/dL.
• Triglycerides: 2.1 ÷ 0.0113 = 186 mg/dL – borderline high.
• Creatinine: 95 ÷ 88.4 = 1.07 mg/dL.
• Urea 6.5 mmol/L corresponds to a BUN of 6.5 ÷ 0.357 = 18 mg/dL.
• Vitamin D: 42 ÷ 2.496 = 17 ng/mL – below the 20 ng/mL level considered adequate by the US National Academy of Medicine.

Going the other way works the same: a US report with LDL 130 mg/dL becomes 3.4 mmol/L in UK terms.

Unit conversion by test group

Diabetes and lipids

Glucose, cholesterol and triglycerides are the most frequently converted results. Remember that cholesterol fractions (total, LDL, HDL and non-HDL) all use the same factor, while triglycerides use their own. Diabetes thresholds in both systems are worth memorising: fasting glucose 100 mg/dL = 5.6 mmol/L, 126 mg/dL = 7.0 mmol/L; two-hour OGTT 140 mg/dL = 7.8 mmol/L, 200 mg/dL = 11.1 mmol/L.

Kidney function

Creatinine is reported in mg/dL or µmol/L; eGFR equations in the US use mg/dL, so SI values are divided by 88.4 first. Urea and BUN need special care, as described above. Urine albumin-to-creatinine ratio is reported in mg/g or mg/mmol; 30 mg/g ≈ 3 mg/mmol.

Hormones

Sex hormones, thyroid hormones and cortisol each have their own factors, and the numbers in SI units can look very different – a cortisol of 15 µg/dL is about 414 nmol/L. Some hormones are reported only in international units, which do not need conversion between the US and SI systems.

Vitamins and minerals

Vitamin D is a frequent source of confusion: 30 ng/mL is 75 nmol/L, and 20 ng/mL is 50 nmol/L. Vitamin B12 is reported in pg/mL (US) or pmol/L (SI), and some labs use ng/L, which equals pg/mL. Iron, calcium, magnesium and phosphate each have their own factors.

Converting reference ranges

When you convert a result, also convert the reference range printed on your report, or use the range from the laboratory that tested you. Reference ranges vary between laboratories because of differences in methods and populations, so converting a value from one lab and comparing it with another lab's range can be misleading. Each test page on this site lists typical ranges in both units, but your own report is the authority.

Why unit errors matter for safety

Unit confusion is a recognised source of medical error. Typical problems include:

• Glucose meters set to the wrong unit. A reading of 7.0 interpreted as mg/dL instead of mmol/L would look dangerously low, and 126 interpreted as mmol/L would be impossible. Most meters lock the unit at manufacture, but travellers and people using imported devices should check.
• Medication thresholds. Doses of insulin, potassium or other treatments may be tied to lab values; applying a US threshold to an SI result, or vice versa, can lead to under- or over-treatment.
• Research and online information. Articles and calculators from different countries may quote thresholds in different units without making it obvious.
• Electronic records. When results from different laboratories are combined, unit mismatches can produce misleading trends on a graph.

A simple habit prevents most of these errors: always read the unit before the number, and when in doubt, ask the laboratory.

Which unit should you use?

Use the unit your clinician and laboratory use, so that results are comparable over time and with their reference ranges. If you move country or see a new clinician abroad, bring copies of previous results with units clearly shown. For research, many journals now request SI units, often with conventional units in brackets.

Tips for reading international lab reports

1. Find the unit next to each value, not just the number.
2. Check whether the test name matches – BUN versus urea, phosphorus versus phosphate, total versus free hormone.
3. Use the correct factor for that specific substance.
4. Compare with the reference range on the same report.
5. Be cautious with hormone units – IU-based results may not be directly comparable between assays.

When to see a doctor

Unit conversion helps you understand a result, but it does not replace interpretation by a clinician who knows your history. If a converted value falls outside the reference range on your report, or if you are unsure which unit was used, ask your clinician or the laboratory. Never change medicines – especially insulin or other diabetes treatment – based on a conversion you are unsure about.