US labs report most blood tests in conventional units, such as mg/dL. UK labs use SI (international) units, such as mmol/L. Your result is the same either way. Only the number changes. Each test has its own conversion factor, because the factor depends on how heavy that molecule is. Three worked examples:
- Glucose: 100 mg/dL × 0.05551 = 5.6 mmol/L
- Cholesterol: 200 mg/dL × 0.0259 = 5.18 mmol/L
- Vitamin D: 20 ng/mL × 2.496 = 50 nmol/L
To go the other way, divide by the same factor. Some tests need no conversion at all: TSH, ferritin and PSA give the same number in both systems. HbA1c uses an equation instead of a factor (6.5% is 48 mmol/mol).
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Blood test unit converter
Choose the test, type the number from your report and pick the unit printed next to it. You’ll see the same result in the other system. Everything is worked out on your device, and nothing is saved or sent anywhere.
Blood test conversion table: US and UK units
Multiply a US result by the first factor to get the UK (SI) unit. To go back, multiply by the second factor. The second factor is rounded to 4 significant figures, so for exact work divide by the first factor instead, as the converter does.
On a phone, swipe the table sideways to see every column.
| Test | US unit | UK / SI unit | US → UK: multiply by | UK → US: multiply by | Example |
|---|---|---|---|---|---|
| Blood sugar | |||||
| Glucose | mg/dL | mmol/L | × 0.05551 | × 18.01 | 100 mg/dL = 5.6 mmol/L |
| HbA1c | % | mmol/mol | Equation, not a factor: mmol/mol = (% − 2.152) ÷ 0.09148 | 6.5% = 48 mmol/mol | |
| Cholesterol and other fats | |||||
| Total cholesterol | mg/dL | mmol/L | × 0.0259 | × 38.61 | 200 mg/dL = 5.18 mmol/L |
| LDL cholesterol | mg/dL | mmol/L | × 0.0259 | × 38.61 | 100 mg/dL = 2.59 mmol/L |
| HDL cholesterol | mg/dL | mmol/L | × 0.0259 | × 38.61 | 40 mg/dL = 1.04 mmol/L |
| Non-HDL cholesterol | mg/dL | mmol/L | × 0.0259 | × 38.61 | 130 mg/dL = 3.37 mmol/L |
| Triglycerides | mg/dL | mmol/L | × 0.0113 | × 88.5 | 150 mg/dL = 1.70 mmol/L |
| Kidneys and gout | |||||
| Creatinine | mg/dL | µmol/L | × 88.4 | × 0.01131 | 1.0 mg/dL = 88 µmol/L |
| BUN (US) / urea (UK) | mg/dL | mmol/L (urea) | × 0.357 | × 2.801 | 14 mg/dL = 5.0 mmol/L |
| Uric acid (urate) | mg/dL | µmol/L | × 59.5 | × 0.01681 | 6.0 mg/dL = 357 µmol/L |
| Minerals and salts | |||||
| Calcium | mg/dL | mmol/L | × 0.25 | × 4 | 9.5 mg/dL = 2.38 mmol/L |
| Magnesium | mg/dL | mmol/L | × 0.4114 | × 2.431 | 2.0 mg/dL = 0.82 mmol/L |
| Phosphate (phosphorus) | mg/dL | mmol/L | × 0.323 | × 3.096 | 3.5 mg/dL = 1.13 mmol/L |
| Potassium | mEq/L | mmol/L | 1 (same number) | 1 (same number) | 4.2 mEq/L = 4.2 mmol/L |
| Sodium | mEq/L | mmol/L | 1 (same number) | 1 (same number) | 140 mEq/L = 140 mmol/L |
| Liver and proteins | |||||
| Bilirubin | mg/dL | µmol/L | × 17.1 | × 0.05848 | 1.0 mg/dL = 17 µmol/L |
| Albumin | g/dL | g/L | × 10 | × 0.1 | 4.0 g/dL = 40 g/L |
| Total protein | g/dL | g/L | × 10 | × 0.1 | 7.0 g/dL = 70 g/L |
| Blood count | |||||
| Hemoglobin (UK: haemoglobin) | g/dL | g/L | × 10 | × 0.1 | 13.5 g/dL = 135 g/L |
| Platelets | ×10³/µL (K/µL) | ×10⁹/L | 1 (same number) | 1 (same number) | 250 ×10³/µL = 250 ×10⁹/L |
| White blood cells | ×10³/µL (K/µL) | ×10⁹/L | 1 (same number) | 1 (same number) | 6.5 ×10³/µL = 6.5 ×10⁹/L |
| Iron and vitamins | |||||
| Ferritin | ng/mL | µg/L | 1 (same number) | 1 (same number) | 50 ng/mL = 50 µg/L |
| Iron (serum) | µg/dL | µmol/L | × 0.179 | × 5.587 | 100 µg/dL = 17.9 µmol/L |
| Vitamin D (25-hydroxy) | ng/mL | nmol/L | × 2.496 | × 0.4006 | 20 ng/mL = 50 nmol/L |
| Vitamin B12 | pg/mL | ng/L (same number) or pmol/L | × 0.738 | × 1.355 | 300 pg/mL = 221 pmol/L |
| Folate (serum) | ng/mL | µg/L (same number) or nmol/L | × 2.265 | × 0.4415 | 5.0 ng/mL = 11.3 nmol/L |
| Thyroid | |||||
| TSH | µIU/mL | mIU/L or mU/L | 1 (same number) | 1 (same number) | 2.5 µIU/mL = 2.5 mIU/L |
| Free T4 | ng/dL | pmol/L | × 12.87 | × 0.0777 | 1.2 ng/dL = 15.4 pmol/L |
| Free T3 | pg/mL | pmol/L | × 1.54 | × 0.6494 | 3.2 pg/mL = 4.9 pmol/L |
| Hormones | |||||
| Testosterone (total) | ng/dL | nmol/L | × 0.0347 | × 28.82 | 500 ng/dL = 17.4 nmol/L |
| Estradiol | pg/mL | pmol/L | × 3.671 | × 0.2724 | 50 pg/mL = 184 pmol/L |
| Cortisol (blood) | µg/dL | nmol/L | × 27.6 | × 0.03623 | 10 µg/dL = 276 nmol/L |
| Inflammation and prostate | |||||
| C-reactive protein (CRP) | mg/dL | mg/L | × 10 | × 0.1 | 0.5 mg/dL = 5.0 mg/L |
| PSA | ng/mL | µg/L | 1 (same number) | 1 (same number) | 4.0 ng/mL = 4.0 µg/L |
Factors come from the Mayo Clinic Laboratories, Labcorp and Quest Diagnostics conversion tables, cross-checked with the Merck Manuals SI calculator. HbA1c uses the NGSP equation. Full references are at the end of this page.
Why US and UK lab reports use different units
Most US labs report chemistry tests in conventional units. These weigh the substance in a set amount of blood, for example milligrams per decilitre (mg/dL). A decilitre is a tenth of a litre. Labcorp and Mayo Clinic Laboratories call these conventional units. Quest Diagnostics calls them gravimetric, which means by weight.
NHS labs in the UK use SI units, from the International System of Units. For many tests, SI units count molecules instead of weighing them, in millimoles per litre (mmol/L) or micromoles per litre (µmol/L). It’s the same blood and the same result, described another way.
To turn a weight into a count of molecules, you need to know how heavy one molecule is. That’s why every test has its own factor. Glucose and cholesterol are both reported in mmol/L in the UK, yet their factors are 0.05551 and 0.0259. No single mg/dL-to-mmol/L factor works for every test.
A few patterns make reports easier to read:
- Some SI units are still weights. Hemoglobin, albumin and total protein go from g/dL to g/L, which is simply × 10. CRP goes from mg/dL to mg/L, also × 10.
- Some units only look different. ng/mL and µg/L are the same number. So are pg/mL and ng/L. Each pair describes the same amount, once per millilitre and once per litre.
- Some hormones use international units (IU). TSH is reported this way in both countries, so there’s nothing to convert.
- HbA1c has its own scale. US labs report a percentage (NGSP units). UK labs report mmol/mol (IFCC units). They’re linked by an equation, NGSP % = 0.09148 × IFCC + 2.152. Because the two scales don’t meet at zero, multiplying by one number won’t work.
Tests that need no conversion
For these tests, US and UK reports give the same number, even when the unit is written differently.
| Test | US report | UK report | Why it’s the same |
|---|---|---|---|
| TSH | µIU/mL | mIU/L or mU/L | Labcorp and Quest list a factor of 1 |
| Ferritin | ng/mL | µg/L (mcg/L) | Labcorp lists a factor of 1 |
| PSA | ng/mL | µg/L | Mayo Clinic Laboratories (ng/mL) and North Bristol NHS Trust (µg/L) print the same age cut-offs: 2.5, 3.5, 4.5 and 6.5 |
| Sodium and potassium | mEq/L | mmol/L | Labcorp and Merck Manuals list a factor of 1 |
| Platelets and white cells | ×10³/µL (K/µL, K/mm³) | ×10⁹/L | A litre holds a million microlitres, so thousands per microlitre equals billions per litre |
| Vitamin B12 | pg/mL | ng/L | Both mean billionths of a gram per litre |
| Folate | ng/mL | µg/L | Both mean millionths of a gram per litre |
B12 and folate can also be reported in molar units, pmol/L and nmol/L, which do need converting. NICE quotes B12 both ways: 180 ng/L is 133 pmol/L. The converter handles all three units for both tests.
Tests you can’t convert reliably
For a few tests, there’s no single trustworthy factor. These appear in the converter’s list so you can find them, but it explains the problem instead of giving a number.
Lipoprotein(a), or Lp(a)
Lp(a) can be reported by weight (mg/dL) or by number of particles (nmol/L). The protein that defines Lp(a) comes in many sizes, and most people carry a mix of them, so the weight of one particle varies from person to person. The HEART UK consensus statement (2019) says converting between the two units “introduces inaccuracy and should be discouraged”, and it recommends reporting in nmol/L. The 2026 US dyslipidemia guideline (ACC/AHA) states its threshold in both units, 125 nmol/L or 50 mg/dL. Those are two cut-offs, one for each unit. They don’t give you a factor to apply to your own result. Compare your number with a cut-off written in the same unit. Our Lp(a) guide explains what the levels mean.
Insulin
Labcorp treats µIU/mL and mIU/L as the same number, so that step is easy. Converting insulin to pmol/L is another matter. Mayo Clinic Laboratories multiplies µIU/mL by 6.95, while Quest Diagnostics multiplies by 7.175. Because the answer depends on the lab, we don’t convert insulin to pmol/L. If you need it, ask the lab that ran your test. Read more about insulin resistance.
Prolactin
US labs report prolactin in ng/mL, which Mayo Clinic Laboratories and Labcorp treat as the same number as µg/L. UK labs, such as Oxford University Hospitals, report it in mU/L (also written mIU/L). None of the three US lab conversion tables we checked gives a factor between ng/mL and mU/L. Quest converts ng/mL to nmol/L instead (× 0.04348), which is a third unit again. So we don’t convert prolactin. Compare your result with the range on your own report, and see our prolactin levels guide.
Reading a US report in the UK, or a UK report in the US
Converting the number is only the first step. A good detective also checks which yardstick it’s being measured against.
- Check the unit next to every number. A hemoglobin of 13.5 g/dL and one of 135 g/L are the same result. Mix up the units and it looks ten times too high or too low.
- Use the range printed on your own report. A result is high or low only compared with the range from the lab that ran it, and ranges differ between labs even in the same unit. For vitamin B12, Labcorp uses 232–1245 pg/mL, while Mayo Clinic Laboratories uses 180–914 ng/L, which is the same unit.
- If you compare with another country’s range, convert both ends with the same factor. Labcorp’s vitamin D range of 20–100 ng/mL becomes about 50–250 nmol/L. An NHS lab such as University Hospitals of North Midlands uses 50.1–200 nmol/L.
- Guideline cut-offs can differ even after converting. For HbA1c, the American Diabetes Association counts 5.7% (39 mmol/mol) and above as prediabetes. NICE in the UK starts its high-risk range at 42 mmol/mol (6.0%). Each country’s doctors follow their own guideline. See our blood sugar and HbA1c guide.
- H and L flags belong to that lab. A flag only means the result is outside that lab’s range. It isn’t a diagnosis.
- Moving between countries? Keep copies of past reports with the units and ranges visible. Your new clinician can then compare like with like, and our health tools accept both unit systems.
Blood test unit questions people ask
How do I convert mg/dL to mmol/L?
It depends on the test, because each molecule has a different weight. For glucose, multiply by 0.05551, so 100 mg/dL is 5.6 mmol/L. For cholesterol, multiply by 0.0259. For triglycerides, multiply by 0.0113. For any other test, use the converter or the table on this page.
How do I convert blood sugar from mmol/L to mg/dL?
Divide by 0.05551, which is the same as multiplying by about 18.0. So 7.0 mmol/L is 126 mg/dL, and 5.6 mmol/L is 101 mg/dL.
How do I convert HbA1c from % to mmol/mol?
Use the NGSP/IFCC equation: mmol/mol = (% − 2.152) ÷ 0.09148. That makes 5.7% equal to 39 mmol/mol, 6.0% equal to 42 and 6.5% equal to 48.
Is ng/mL the same as µg/L?
Yes. 1 ng/mL equals 1 µg/L, so ferritin, PSA and folate give the same number in both. In the same way, pg/mL equals ng/L, so a US vitamin B12 result in pg/mL and a UK result in ng/L can be compared directly.
What’s the difference between BUN and urea?
US labs measure blood urea nitrogen (BUN), the nitrogen part of urea, in mg/dL. UK labs report the whole urea molecule in mmol/L. To convert, multiply BUN by 0.357 (Labcorp). A BUN of 14 mg/dL is about 5.0 mmol/L of urea.
How do I convert creatinine from µmol/L to mg/dL?
Divide by 88.4. So 88 µmol/L is 1.00 mg/dL, and 1.2 mg/dL is 106 µmol/L. Read more in our kidney function test guide.
Why do some websites use 2.5 for vitamin D?
It’s a rounded version of 2.496, the factor in Mayo Clinic Laboratories’ table. The NIH Office of Dietary Supplements uses 2.5. The two differ by less than 0.2%, so either is fine for everyday use.
Can I convert Lp(a) from mg/dL to nmol/L?
Not reliably. Lp(a) particles vary in size from person to person, and HEART UK advises against converting. Compare your result with a cut-off written in the same unit.
How we built this tool
Written and medically reviewed by Dr. Mustafa Sakr, MBBCh. Last reviewed: October 2026. Every factor comes from at least one US laboratory’s published conversion table (Mayo Clinic Laboratories, Labcorp or Quest Diagnostics) and agrees with a second source: another lab’s table, the Merck Manuals SI calculator, a guideline’s own paired values, or a plain unit identity such as 1 litre = 10 decilitres. Where tables differ slightly, the converter names the one it uses, and those differences are all under 1%. HbA1c uses the NGSP/IFCC master equation. We left out tests whose conversion depends on the lab’s method. We update this page when guidance changes.
How the converter works: it divides your number by the factor for your unit, then multiplies by the factor for the other unit. Each result is rounded to a fixed number of decimal places for its unit, with halves rounded up, and the converter shows the unrounded figure and the factor it used. Units that give the same number come back exactly as you typed them. The swap button converts the rounded result back, so a round trip can shift slightly (100 mg/dL becomes 5.6 mmol/L, which becomes 101 mg/dL). Everything runs on your device. Nothing is stored or sent, and the tool can’t tell you whether a result is normal for you.
References
- Mayo Clinic Laboratories. SI Unit Conversion (conventional unit × factor = SI unit). mayocliniclabs.com
- Labcorp. SI Unit Conversion Table. labcorp.com
- Quest Diagnostics. International System of Units (SI Units) (PDF). questdiagnostics.com
- Merck Manuals. SI unit to conventional unit conversions: chemistry and endocrine tests (calculator based on Young DS, Ann Intern Med 1987;106:114). merckmanuals.com
- NGSP. IFCC standardization of HbA1c (master equation) and HbA1c conversion table. Master equation · Conversion table
- Cegla J, et al. HEART UK consensus statement on Lipoprotein(a). Atherosclerosis 2019;291:62–70. doi:10.1016/j.atherosclerosis.2019.10.011
- Blumenthal RS, et al. 2026 ACC/AHA multisociety Guideline on the Management of Dyslipidemia. Circulation 2026. AHA: top things to know
- American Diabetes Association. 2. Diagnosis and Classification of Diabetes: Standards of Care in Diabetes 2026. Diabetes Care 2026;49(Suppl 1):S27–S49. doi:10.2337/dc26-S002
- NICE. Type 2 diabetes: prevention in people at high risk (PH38), 2012, updated 2017. nice.org.uk (PDF)
- NICE. Vitamin B12 deficiency in over 16s: diagnosis and management (NG239), 2024. nice.org.uk/guidance/ng239
- NIH Office of Dietary Supplements. Vitamin D: Fact Sheet for Health Professionals. ods.od.nih.gov
- US laboratory test pages: Mayo Clinic Laboratories PSA, vitamin B12 and BUN; Labcorp vitamin B12 and vitamin D; OHSU CBC; Michigan Medicine CRP.
- NHS laboratory test pages: North Bristol NHS Trust PSA; University Hospitals Birmingham urea; Gloucestershire Hospitals haematology ranges and B12 and folate; University Hospitals of North Midlands vitamin D; Oxford University Hospitals prolactin.
This page is for education only and isn’t medical advice, a diagnosis or a substitute for your own doctor, who knows your history. Conversion factors can differ slightly between laboratories, and reference ranges vary between laboratories. Always interpret results with a qualified clinician. See our medical disclaimer.