Peptide Science
Peptide Science

Syringe Draw & Dosage Math: mg, mcg, mL, and Units

February 12, 2026β€’ Peptide Science Editorial
guidedosagemathinsulin-syringe

Core formula

Volume to draw (mL) = target dose Γ· concentration

If concentration is in mg/mL, target dose must be in mg. If concentration is in mcg/mL, target dose must be in mcg.

Unit conversions you must memorize

  • 1 mg = 1000 mcg
  • U-100 insulin syringe: 100 units = 1.0 mL
  • Therefore: 1 unit = 0.01 mL

Worked example 1 (mg-based)

Given concentration = 5 mg/mL, target dose = 0.25 mg:

  1. mL to draw = 0.25 Γ· 5 = 0.05 mL
  2. On a U-100 syringe: 0.05 mL = 5 units

Worked example 2 (mcg-based)

Given concentration = 2000 mcg/mL, target dose = 300 mcg:

  1. mL to draw = 300 Γ· 2000 = 0.15 mL
  2. On a U-100 syringe: 0.15 mL = 15 units

Worked example 3 (from vial amount)

Vial contains 10 mg total, reconstituted with 2 mL total volume.

  • Concentration = 10 Γ· 2 = 5 mg/mL
  • Target 1 mg dose β†’ 1 Γ· 5 = 0.2 mL β†’ 20 units on U-100

Error-prevention checklist

  • Write every step, including units, before drawing.
  • Never mix mg and mcg in the same step without explicit conversion.
  • Double-check concentration after any change in reconstitution volume.
  • When possible, do an independent second check.

Common pitfalls

  • Confusing syringe β€œunits” with drug β€œunits” (they are not universally interchangeable across medications).
  • Using U-100 assumptions on a non-U-100 device.
  • Rounding too aggressively for very small volumes.

Sources