Estradiol (E2) Unit Converter

Q: How do I convert oestradiol from pg/mL to pmol/L?

Multiply by 3.67134, a factor derived from the molecular mass of 17-beta-oestradiol, 272.38 Da. An oestradiol of 120 pg/mL is 441 pmol/L. To go the other way, divide by 3.67134.

Q: Is ng/L the same as pg/mL for oestradiol?

Yes. One nanogram per litre is one picogram per millilitre, so the two are numerically identical and no conversion is needed.

Q: Why does the day of the cycle matter so much?

Oestradiol runs from around 20 pg/mL in the early follicular phase to several hundred at the pre-ovulatory peak. Without the cycle day there is no interval to compare the result against, so the same number can be normal or clearly abnormal.

Q: When should mass spectrometry be used instead of an immunoassay?

Whenever the expected concentration is low: postmenopausal women, women taking aromatase inhibitors, men, and children under assessment for precocious or delayed puberty. Direct immunoassays lose accuracy in that range.

Q: What oestradiol is expected during IVF stimulation?

Values run into the thousands of pg/mL and are followed as a trend alongside follicle counts, to judge response and the risk of ovarian hyperstimulation. No reference interval applies in that setting.

Convert oestradiol between pg/mL, pmol/L and ng/L, and see why a single value means nothing without the day of the cycle.

Last updated 4 Sep 2026

Estradiol (E2) converter

Mass ⇄ molar

Oestradiol

pg/mL × 3.67134 = pmol/L. pg/mL and ng/L are numerically identical.

Reference groupChoose the group that matches the sample. Oestradiol changes several-fold across the cycle, so the day of the cycle must be known before the number can be read.

441pmol/LExample

Oestradiol 120 pg/mL, follicular phase

Formula and conversion factors

pmol/L = pg/mL × 3.67134
pg/mL = pmol/L ÷ 3.67134
ng/L = pg/mL (numerically identical)

3.67134: derived from the molecular mass of 17-beta-oestradiol, 272.38 Da
ng/L: numerically identical to pg/mL; no conversion is needed between them
cycle day: the interval to apply depends on the phase — early follicular, pre-ovulatory peak, mid-luteal or postmenopausal — so the sample date relative to the cycle is part of the result
method: direct immunoassays lose accuracy at low concentrations; mass spectrometry is the reliable method in postmenopausal women, in men and in children

Worked example

Oestradiol 120 pg/mL, follicular phase
120 × 3.67134 = 441 pmol/L
= 120.0 ng/L
Within the follicular phase interval of 20–150 pg/mL

Typical oestradiol by phase, in both units

Figures are representative rather than universal and vary between assays. The pmol/L column is the pg/mL figure multiplied by 3.67134.
	pg/mL	pmol/L
Early follicular	20 – 80	73 – 294
Late follicular, pre-ovulatory peak	150 – 400	551 – 1,469
Mid-luteal	60 – 200	220 – 734
Postmenopausal	< 30	< 110
Adult male	10 – 40	37 – 147

When the assay method matters

Direct immunoassays were designed for the concentrations of the menstrual cycle and lose both accuracy and precision well below them.
Setting	Concentration	Preferred method
Cycle monitoring, ovarian stimulation	High	Immunoassay is adequate and fast enough for serial tracking
Postmenopausal women, including on aromatase inhibitors	Very low	Liquid chromatography–tandem mass spectrometry
Men, and disorders of sex development	Low	Liquid chromatography–tandem mass spectrometry
Children, suspected precocious or delayed puberty	Very low	Liquid chromatography–tandem mass spectrometry

Why the cycle day is part of the result

Oestradiol is reported in pg/mL in the United States and in pmol/L elsewhere, with a factor of 3.67134 between them taken from the molecular mass of 17-beta-oestradiol, 272.38 daltons. An oestradiol of 120 pg/mL is 441 pmol/L. The third unit, ng/L, is numerically identical to pg/mL and needs no conversion. The arithmetic is the least of the problems with this analyte.

Oestradiol changes more across the menstrual cycle than almost any other routine measurement. It sits around 20 to 80 pg/mL in the early follicular phase, climbs through the follicular phase as the dominant follicle matures, and peaks in the hundreds shortly before ovulation, before falling and rising again through the luteal phase. A value quoted without the day of the cycle is therefore uninterpretable: the same 200 pg/mL is unremarkable just before ovulation and clearly abnormal in a postmenopausal woman.

The second difficulty is analytical. Direct immunoassays were built for the concentrations seen in cycling women, and they lose accuracy and precision at the low levels that matter most elsewhere — in postmenopausal women, in women on aromatase inhibitors, in men, and in children being assessed for precocious or delayed puberty. In those settings liquid chromatography–tandem mass spectrometry is the reliable method, and an immunoassay result near the bottom of its range should not be over-read.

In assisted reproduction the number is used differently again. During ovarian stimulation oestradiol rises into the thousands of pg/mL, far outside any reference interval, and it is followed as a trend alongside ultrasound follicle counts to judge response and the risk of ovarian hyperstimulation syndrome. There is no normal range in that context, and comparing a stimulation value with a follicular phase interval is a category error rather than an abnormal result.

Frequently asked questions

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

Multiply by 3.67134, a factor derived from the molecular mass of 17-beta-oestradiol, 272.38 Da. An oestradiol of 120 pg/mL is 441 pmol/L. To go the other way, divide by 3.67134.

Is ng/L the same as pg/mL for oestradiol?

Yes. One nanogram per litre is one picogram per millilitre, so the two are numerically identical and no conversion is needed.

Why does the day of the cycle matter so much?

Oestradiol runs from around 20 pg/mL in the early follicular phase to several hundred at the pre-ovulatory peak. Without the cycle day there is no interval to compare the result against, so the same number can be normal or clearly abnormal.

When should mass spectrometry be used instead of an immunoassay?

Whenever the expected concentration is low: postmenopausal women, women taking aromatase inhibitors, men, and children under assessment for precocious or delayed puberty. Direct immunoassays lose accuracy in that range.

What oestradiol is expected during IVF stimulation?

Values run into the thousands of pg/mL and are followed as a trend alongside follicle counts, to judge response and the risk of ovarian hyperstimulation. No reference interval applies in that setting.

Related calculators

References

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.
National Institute for Health and Care Excellence. Fertility problems: assessment and treatment. NICE clinical guideline CG156. 2013, updated 2017.
Practice Committee of the American Society for Reproductive Medicine. Prevention and treatment of moderate and severe ovarian hyperstimulation syndrome: a guideline. Fertil Steril. 2016;106(7):1634–1647.