For a vial labelled 10 mg with 3 mL of diluent added, the concentration is approximately 3.33 mg/mL. On a U-100 scale, 15 units represents 500 mcg (0.5 mg) and 30 units represents 1,000 mcg (1 mg).
Those numbers apply to this exact 10 mg and 3 mL mixture. Changing either number changes the result.
Quick Reference for 10 mg With 3 mL Diluent
The concentration comes from one calculation:
10 mg / 3 mL = 3.333... mg/mL
On a U-100 scale, 100 units equals 1 mL. The common markings for this mixture are:
| U-100 scale marking | Liquid volume | Amount represented |
|---|---|---|
| 5 units | 0.05 mL | About 167 mcg 0.167 mg |
| 10 units | 0.1 mL | About 333 mcg 0.333 mg |
| 15 units | 0.15 mL | 500 mcg 0.5 mg |
| 20 units | 0.2 mL | About 667 mcg 0.667 mg |
| 25 units | 0.25 mL | About 833 mcg 0.833 mg |
| 30 units | 0.3 mL | 1,000 mcg 1 mg |
| 50 units | 0.5 mL | About 1,667 mcg 1.667 mg |
A 20 mg Vial With 3 mL Diluent
With the same 3 mL of diluent added to a 20 mg vial, the concentration is approximately 6.67 mg/mL:
20 mg / 3 mL = 6.666... mg/mL
The vial contains twice as much compound in the same liquid volume as the 10 mg example. Each U-100 scale marking therefore represents twice the amount.
| U-100 scale marking | Liquid volume | Amount represented |
|---|---|---|
| 10 units | 0.1 mL | About 667 mcg 0.667 mg |
| 15 units | 0.15 mL | 1,000 mcg 1 mg |
| 30 units | 0.3 mL | 2,000 mcg 2 mg |
Compared with the 10 mg vial, every marking represents twice as much because the diluent volume stays at 3 mL. At 15 units the amount changes from 500 mcg (0.5 mg) to 1,000 mcg (1 mg); at 30 units it changes from 1,000 mcg (1 mg) to 2,000 mcg (2 mg).
Changing the Diluent Volume
The vial still contains 10 mg in each example below. The diluent volume changes the concentration and the scale marking that represents 1 mg.
| diluent added | Concentration | U-100 scale marking for 1 mg |
|---|---|---|
| 1 mL | 10 mg/mL | 10 units |
| 2 mL | 5 mg/mL | 20 units |
| 3 mL | About 3.33 mg/mL | 30 units |
More diluent spreads the same 10 mg through a larger volume, so the same milligram amount occupies more U-100 units.
Calculating Another U-100 Marking
First find the concentration:
Concentration = vial amount (mg) / diluent volume (mL)
Then convert the amount being calculated into U-100 units:
U-100 units = amount (mg) / concentration (mg/mL) x 100
For the 10 mg and 3 mL example, 500 mcg (0.5 mg) works out to 15 units:
0.5 / 3.333... x 100 = 15 units
For 1,000 mcg (1 mg), the result is 30 units:
1 / 3.333... x 100 = 30 units
The Peptide Reconstitution Calculator can check the same arithmetic after the vial amount, diluent volume and U-100 scale value are entered.
Check the U-100 Scale
These conversions apply to a U-100 scale, where 100 units equals 1 mL and 10 units equals 0.1 mL. Printed U-100 scales can use half-unit, 1-unit or 2-unit spacing, so read the numbers and line interval on the specific scale before counting markings.
This page explains the conversion between vial mg, liquid mL and U-100 scale markings. It does not select an amount or frequency.
Sources and context
NIST metric prefixes: Metric (SI) Prefixes. NIST records the relationship between milligrams and micrograms.
Research-use notice: Precision Synthetics Canada products and documentation are provided strictly for lawful, non-clinical laboratory research purposes only. COAs and testing records are not medical documents, safety guarantees, sterility guarantees, therapeutic endorsements, dosing guidance, or approval for human or veterinary use.