Estradiol Unit Converter

The conversion is easy. The measurement is not.

An estradiol result is a mass of hormone in a volume of blood. The United States reports it in picograms per millilitre; the United Kingdom, Europe, Australia and Canada report the same blood in picomoles per litre, which counts molecules instead. Getting from one to the other means dividing by the mass of one mole of estradiol. Nothing else is involved, and the conversion does not depend on which laboratory ran the test. One quirk worth knowing first: 1 pg/mL and 1 ng/L are the same quantity written two ways, so a report in ng/L needs no conversion at all.

Estradiol is C18H24O2. PubChem (CID 5757) reports its molecular weight to four significant figures as 272.4 g/mol; the value used throughout the endocrine literature, and by this page, is 272.38 g/mol. One pg/mL is 1 × 10⁻⁹ g/L; divide by 272.38 g/mol and you get 3.6713415 pmol/L. Round to four significant figures and you have the 3.671 everybody prints.

We then did to estradiol what this site's testosterone converter does to testosterone: sourced the molar mass properly, from NIST's standard atomic weights, which are published as intervals rather than points because the isotopic composition of ordinary terrestrial material genuinely varies. Carbon is [12.0096, 12.0116], hydrogen [1.00784, 1.00811], oxygen [15.99903, 15.99977]. Run those through C18H24O2 and estradiol's molar mass is anywhere from 272.359 to 272.403 g/mol, so the factor is an interval too: 3.6710318 to 3.6716243.

And here the result is the opposite of the testosterone one, which is worth reporting because we expected otherwise. For testosterone the printed 0.0347 sits 0.075% ABOVE the top of its interval — outside it. For estradiol the printed 3.671 sits 0.00087% below the bottom of its interval, which is eighty-six times closer and, at the four significant figures it is quoted to, indistinguishable. The interval is itself only 0.016% wide. At 30 pg/mL every defensible factor lands between 110.130 and 110.149 pmol/L — a total disagreement of 0.019 pmol/L, or 0.0051 pg/mL. The printed factor is right. Use it.

That is the whole arithmetic, and it is not why this page is here. The number that does move is the measurement. Estradiol in men is low — low enough that it sits at or beneath the bottom of the range the automated immunoassay in most hospital laboratories was built for. The Endocrine Society's 2013 position statement puts it bluntly, listing among its recommendations "a wider recognition among physicians, laboratorians, and investigators of the fact that the low E2 values seen in men, children, and menopausal women, which are obtained from direct assays, eg, those done on whole serum without prior extraction, are not likely to be trustworthy". A CDC study of 11 immunoassays and 6 mass spectrometry methods found that "most assays are not able to measure E2 levels below 10 pg/mL" at all.

The size of the gap is the part that should change how you read your own report. In the European Male Ageing Study, 3,174 men had estradiol measured twice on the same blood, once by a standard platform immunoassay and once by gas chromatography–mass spectrometry. Above 120 pmol/L (32.7 pg/mL) the two agreed reasonably, at R = 0.74. Below 40.8 pmol/L (11.1 pg/mL) the correlation collapsed to R = 0.32, and the immunoassay identified low estradiol with 13.3% sensitivity. The authors' conclusion was that the immunoassay "may only be suitable for the detection of high E2 in men". A separate comparison in 6,195 men across three cohorts found the two methods correlated between 0.53 and 0.76. Set that beside the 0.0051 pg/mL the conversion arithmetic is worth.

Even a laboratory that has proved its accuracy is allowed a wide margin. The CDC runs a Hormone Standardization Programme (HoSt) for estradiol as well as testosterone, assigning reference values with an isotope-dilution HPLC–tandem mass spectrometry reference procedure. To be certified an assay must come within ±12.5% of that reference above 20 pg/mL, and within ±2.5 pg/mL at or below it. At 30 pg/mL that permits anything from 26.25 to 33.75 pg/mL — a band 7.50 pg/mL wide, about 2700 times the entire rounding argument above, from an assay that has passed. Uncertified assays are not bound by even that. This is why "sensitive estradiol" and "estradiol by LC-MS/MS" exist as separate orderable tests, and why a result from one is not interchangeable with a result from the other.

WHAT THIS PAGE WILL NOT TELL YOU. There is no established reference range for estradiol in men, and none whatsoever for men on testosterone therapy. The Endocrine Society's 2018 guideline sets out the monitoring plan for men on testosterone and estradiol is not in it: it says clinicians should monitor "evaluating symptoms, adverse effects, and compliance; measuring serum T and hematocrit concentrations; and evaluating prostate cancer risk during the first year". Its 2013 position statement lists "reference ranges for E2 that are age- and gender-specific" among the things still needed. A harmonized reference range for estradiol was finally published in 2026 — for postmenopausal women, in 7,206 of them, and the paper says nothing about men. The specific "optimal E2" numbers that circulate on forums, usually 20–30 pg/mL or a testosterone-to-estradiol ratio, trace to no primary source we could find. This converter will change the units on your number and will not tell you what it should be.

Estradiol conversion chart — pg/mL to pmol/L

Find the pg/mL figure on your US report on the left; the pmol/L column is what a UK, European, Australian or Canadian report would show for the same blood.

NO ROW HERE IS MARKED NORMAL OR LOW, and that is deliberate: no reference range for estradiol in men has been established, and none at all for men on testosterone therapy. The difference column is the entire cost of the printed 3.671: never as much as 0.051 pmol/L anywhere on this table. The ng/L note under each row is not a conversion — a picogram per millilitre and a nanogram per litre are the same quantity. Every figure computed by the same function the converter above calls.

Estradiol conversion chart — pmol/L to pg/mL

The other direction, for a report issued in SI units. Divide pmol/L by the printed factor, or multiply by the molar mass over a thousand — they give the same answer.

The 110 and 120 pmol/L rows are there because the European Male Ageing Study reported its estradiol thresholds for men in pmol/L, and a US reader needs them in pg/mL to use them. Unlike testosterone, estradiol has no separately printed reverse factor — journals say "divide by 3.671" — so converting out and back returns you to exactly where you started, with no drift. The difference column above is the gap between that division and the molar-mass multiplication, and it never reaches a hundredth of a pg/mL on this table.

Every route to the conversion factor, compared

The same conversion derived six ways. Four are defensible and agree to within 0.016%; one is the figure in common use, and it is among them; one is the wrong quantity entirely.

The first two rows are the bounds NIST's standard atomic weight intervals put on the molar mass of C18H24O2; everything between them is permitted by natural isotopic variation. The printed 3.671 sits 0.00087% below the bottom of that interval — for comparison, this site's testosterone converter found the printed 0.0347 sitting 0.075% above the top of the equivalent testosterone interval, eighty-six times further out. The last row is the trap: PubChem's ExactMass, 272.177630004, is the monoisotopic mass — the mass of a single molecule in which every carbon is ¹²C — not a molar mass. For testosterone that mistake hides, because it happens to round to the printed factor. For estradiol it shows: it gives 3.6741, not 3.671. It is still only 0.074% out, which tells you how little any of this matters.

What a CDC-certified estradiol assay is allowed to report

The bias the CDC Hormone Standardization Programme permits an assay to carry and still be certified: ±12.5% above 20 pg/mL, ±2.5 pg/mL at or below it. Read the row for a true concentration; the range is what a passing assay may return.

Source: Participant Protocol for CDC Hormone Standardization (CDC HoSt) Program, Estradiol (E2), which sets an "allowable bias of +12.5 % for the samples with estradiol reference value >20 pg/mL" and "allowable bias of +2.5 pg/mL for the samples with estradiol reference value ≤20 pg/mL", against reference values assigned by a procedure "which uses ID-HPLC/MS/MS and certified primary standards from the National Metrology Institute of Japan (NMIJ)". The last column is the point of the whole page: the tolerance a certified assay carries is thousands of times the entire conversion-factor argument, and it widens in relative terms as the concentration falls — which is exactly where men are measured. THIS IS NOT AN ERROR BAR ON YOUR OWN RESULT and it is not a reference range; it is what the standardisation programme permits. An assay that is not enrolled is not bound by it at all. One source disagreement worth naming: the CDC protocol puts 20 pg/mL itself in the absolute-bias group while Vesper 2014 puts it in the relative one. Both give ±2.5 pg/mL at exactly 20, so nothing here changes.

Estradiol figures published for men, in both units

The numbers the primary literature actually states, converted. Much of the research on estradiol in men is European and reports in pmol/L; a US reader needs them in pg/mL before they are any use.

THIS IS NOT A REFERENCE RANGE AND MUST NOT BE READ AS ONE. Each row is one number from one named paper, converted — a method-comparison breakpoint, a detection floor, a programme criterion, or a mean in a described group of men. Nothing here is a threshold for any individual, and the two postmenopausal-women rows are included precisely because that is the only harmonized estradiol reference range anyone has published: there is no male equivalent. The two Cui 2026 rows double as a check on our arithmetic — that paper printed 4.0 and 66.8 pmol/L beside its 1.1 and 18.2 pg/mL, and both the derived factor and the printed 3.671 reproduce those figures exactly.

Frequently asked questions

How do I convert estradiol from pg/mL to pmol/L?

Multiply pg/mL by 3.671. An estradiol of 20 pg/mL is 73.4 pmol/L; 30 pg/mL is 110.1 pmol/L; 50 pg/mL is 183.6 pmol/L. The factor is the molar mass of estradiol, 272.38 g/mol, rearranged as 1000 ÷ M, and nothing about it depends on your laboratory or your assay. To go back the other way, divide by 3.671.

Is the 3.671 estradiol conversion factor accurate?

Yes — and we checked it the hard way, expecting it not to be. Derived from the molar mass the factor is 3.6713415, and NIST's standard atomic weight intervals put it between 3.6710318 and 3.6716243, so 3.671 sits just 0.00087% below the bottom of that range. At 30 pg/mL the entire disagreement between every defensible factor is 0.019 pmol/L, which is 0.0051 pg/mL. By contrast, the same exercise on testosterone found the printed 0.0347 sitting 0.075% outside its interval — eighty-six times further out.

What is 30 pg/mL of estradiol in pmol/L?

110.14 pmol/L, or 110.13 pmol/L if you use the printed 3.671 — the two agree to three decimal places. In nmol/L the same result is 0.1101, and in ng/L it is simply 30, because a ng/L and a pg/mL are the same thing. What 30 pg/mL means for a man is a separate question this page does not answer, because no reference range for estradiol in men has been established.

Why is my estradiol different at two different labs?

Almost certainly the assay, not the arithmetic. In the European Male Ageing Study, 3,174 men had estradiol measured on the same blood by a platform immunoassay and by mass spectrometry: below 40.8 pmol/L (11.1 pg/mL) the two correlated at only R = 0.32, and the immunoassay detected low estradiol with 13.3% sensitivity. A CDC study of 17 methods found mean bias against the reference method ranging from −2.4% to 235%, with only three of the 17 meeting the ±12.5% criterion. A certified assay at a true 30 pg/mL may report anywhere from 26.25 to 33.75 pg/mL. The conversion factor accounts for 0.0051 pg/mL of that.

What is a sensitive estradiol test, and do men need one?

A "sensitive estradiol" or "estradiol by LC-MS/MS" test is a different measurement method, not a more careful version of the same one. It exists because male estradiol concentrations sit at the bottom of what a routine immunoassay can resolve — a CDC study of 11 immunoassays and 6 mass spectrometry methods concluded that "most assays are not able to measure E2 levels below 10 pg/mL". The Endocrine Society states that low estradiol values in men from direct assays "are not likely to be trustworthy". Whether you need one is a question for whoever ordered the test; what is certain is that a result from one method should not be compared with a result from the other.

What is the optimal estradiol level for a man on TRT?

This page will not give you a number, because no established one exists. The Endocrine Society's 2018 guideline sets out what to monitor in men on testosterone therapy — symptoms, adverse effects, compliance, serum testosterone, haematocrit and prostate cancer risk — and estradiol is not on that list. Its 2013 position statement lists age- and gender-specific estradiol reference ranges among the things still needed. The only harmonized estradiol reference range published to date, in 2026, covers 7,206 postmenopausal women and says nothing about men. The 20–30 pg/mL figures and testosterone-to-estradiol ratios circulated on forums trace to no primary source. Discuss your result with the clinician who ordered it.

Is estradiol reported in ng/L the same as pg/mL?

Yes, exactly the same — 1 pg/mL = 1 ng/L, with no factor involved. A decilitre is 100 millilitres and a litre is 1,000, so the picogram-per-millilitre and nanogram-per-litre figures coincide: 25 ng/L is 25 pg/mL is 91.8 pmol/L. This trips people up because every other hormone conversion on a lab report involves a factor, so readers assume this one must too and look for a number that is not there.

Why does the research state estradiol in pmol/L when my report says pg/mL?

Because most of the large studies of estradiol in men are European, and Europe reports in SI units. The European Male Ageing Study's method-comparison thresholds are 40.8 pmol/L and 120 pmol/L, which are 11.1 and 32.7 pg/mL. Without converting them, a US reader cannot tell whether a paper's finding applies to the number on their own report — which is the main practical use of this converter, and the reason the chart above prints the published figures in both units.

Sources

1. [1]PubChem Compound Summary CID 5757 (estradiol) — MolecularFormula "C18H24O2", MolecularWeight "272.4", ExactMass "272.177630004"
2. [2]NIST Atomic Weights and Isotopic Compositions — standard atomic weights of carbon [12.0096,12.0116], hydrogen [1.00784,1.00811] and oxygen [15.99903,15.99977]
3. [3]Nassan FL, Jensen TK, Priskorn L, et al. Association of Dietary Patterns With Testicular Function in Young Danish Men. JAMA Netw Open. 2020;3(2):e1921610 — SI footnote: "to picomoles per liter, multiply by 3.671"
4. [4]Rosner W, Hankinson SE, Sluss PM, Vesper HW, Wierman ME. Challenges to the Measurement of Estradiol: An Endocrine Society Position Statement. J Clin Endocrinol Metab. 2013;98(4):1376–1387 — low estradiol in men from direct assays is "not likely to be trustworthy"
5. [5]Huhtaniemi IT, Tajar A, Lee DM, et al. Comparison of serum testosterone and estradiol measurements in 3174 European men using platform immunoassay and mass spectrometry. Eur J Endocrinol. 2012;166(6):983–991 — R = 0.32 below 40.8 pmol/L, 13.3% sensitivity for low E2
6. [6]Ohlsson C, Nilsson ME, Tivesten A, et al. Comparisons of immunoassay and mass spectrometry measurements of serum estradiol levels and their influence on clinical association studies in men. J Clin Endocrinol Metab. 2013;98(6):E1097–E1102 — Spearman correlation 0.53–0.76 across three male cohorts
7. [7]Vesper HW, Botelho JC, Vidal ML, Rahmani Y, Thienpont LM, Caudill SP. High variability in serum estradiol measurements in men and women. Steroids. 2014;82:7–13 — "Most assays are not able to measure E2 levels below 10 pg/mL"
8. [8]Participant Protocol for CDC Hormone Standardization (CDC HoSt) Program, Estradiol (E2), updated 26 April 2023 — the ±12.5% and ±2.5 pg/mL certification criteria and the ID-HPLC/MS/MS reference measurement procedure
9. [9]Cui J, Hankinson SE, Matsumoto AM, et al. Establishment of harmonized international reference ranges for plasma estradiol concentrations in postmenopausal women. J Clin Endocrinol Metab. 2026;111(10):2745–2755 — the only harmonized estradiol reference range published, and it is not for men
10. [10]Bhasin S, Brito JP, Cunningham GR, et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2018;103(5):1715–1744 — the monitoring plan for men on testosterone, which does not include estradiol