mcg/mL: Micrograms per mL and Per-Mark Math
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[Glossary · Mixing and measuring]

mcg/mL (micrograms per milliliter)

Also called mcg per mL, µg/mL, ug/mL, micrograms per milliliter · Reviewed

Definition: mcg/mL (micrograms per milliliter) is a strength written in micrograms, each a thousandth of a milligram. It equals mg/mL times 1,000, so 0.25 mg/mL is 250 mcg/mL. Writing a weak solution in mcg/mL keeps the numbers whole. The Forteo label, for example, gives its strength as 250 mcg/mL.

Converting, and the per-mark number

NIST defines milli as a thousandth and micro as a millionth, so 1 mg = 1,000 mcg and 1 mg/mL = 1,000 mcg/mL. One mark on a U-100 syringe is 0.01 mL (100 marks per mL), so the micrograms in one mark is the mcg/mL divided by 100.

mg/mL, mcg/mL and mcg in one U-100 mark (0.01 mL)
mg/mLmcg/mLmcg per mark
0.252502.5
0.55005
11,00010
22,00020
44,00040

Worked examples

Forteo pen: label strength to total

  1. The label gives 250 mcg/mL and a fill of 2.24 mL.
  2. 250 × 2.24 = 560 mcg, which matches the "560 mcg/2.24 mL" on the label.
  3. Per 0.01 mL: 250 ÷ 100 = 2.5 mcg.

A strength that does not divide evenly (made-up vial: 10 mg in 3 mL)

  1. 10 mg ÷ 3 mL = 3.333 mg/mL = 3,333 mcg/mL (rounded).
  2. Per mark: 3,333 ÷ 100 = 33.3 mcg.
  3. Rounding early adds up: 10 marks at 33 mcg is 330 mcg, while 10 marks at 33.33 mcg is 333 mcg.

Common mix-ups

mcg/mL and mg/mL differ by 1,000 times, so a misplaced unit is a large error. "µg/mL" and "ug/mL" mean the same as mcg/mL. For plain weight conversions, see mcg vs mg.

Read more on Dose Track: Peptide reconstitution calculator · The reconstitution helper in Dose Track

General education drawn from labels and published studies, not personal medical advice. Your prescriber, pharmacist and the label that came with your product are the final word.
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Frequently asked questions

How do I convert mg/mL to mcg/mL?+
Multiply by 1,000. 2.5 mg/mL is 2,500 mcg/mL. To go back, divide by 1,000.
How many mcg are in one mark of a U-100 syringe?+
One mark is 0.01 mL, so divide the mcg/mL by 100. At 2,000 mcg/mL, one mark holds 20 mcg.
Is µg/mL the same as mcg/mL?+
Yes. µg, ug and mcg all mean microgram.

Sources

  1. NIST: Metric (SI) prefixes
  2. Forteo (teriparatide injection) US prescribing information, DailyMed
  3. Humulin R U-100 (insulin human) US prescribing information, DailyMed

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