Insulin syringes measure volume in "units," not milliliters. On every standard U-100 insulin syringe, 100 units equals 1ml. This means each unit is 0.01ml. Once you know that conversion, every peptide dose calculation becomes straightforward.
Syringe Sizes
Insulin syringes come in three common sizes. The internal scale differs, but the unit-to-ml ratio is always the same.
100-Unit Syringe (1ml)
- Total capacity: 100 units (1.0ml)
- Markings: Every 2 units, with numbered lines at 10, 20, 30, etc.
- Best for: Larger doses, reconstituting (adding water to the vial)
This is the most common syringe. It holds the most volume, which makes it useful for reconstitution and for peptides that require larger injection volumes. The downside is that small doses (under 10 units) are harder to measure precisely because the markings are close together.
50-Unit Syringe (0.5ml)
- Total capacity: 50 units (0.5ml)
- Markings: Every 1 unit, with numbered lines at 5, 10, 15, etc.
- Best for: Medium doses, good balance of precision and capacity
The 50-unit syringe is a solid middle ground. Individual unit lines are spaced farther apart than on the 100-unit syringe, making small increments easier to read. Many users prefer this size for daily peptide dosing.
30-Unit Syringe (0.3ml)
- Total capacity: 30 units (0.3ml)
- Markings: Every 1 unit (sometimes every 0.5 units), numbered at 5, 10, 15, etc.
- Best for: Small, precise doses
The 30-unit syringe offers the highest precision. Each unit marking is wide and easy to read. If your calculated dose is under 30 units, this syringe gives you the most accurate measurement. Ideal for peptides like BPC-157 (typical doses of 5-10 units) or sermorelin.
How to Read the Markings
Hold the syringe at eye level with the needle pointing up. The plunger has a rubber gasket inside the barrel. Read the volume at the top edge of the gasket (the edge closest to the needle), not the bottom edge.
Example on a 100-unit syringe:
- The plunger's top rubber edge sits at the "10" line = 10 units = 0.1ml
- Halfway between "10" and "20" = 15 units = 0.15ml
- At the "5" line = 5 units = 0.05ml
Quick conversion table:
| Units | Milliliters | |---|---| | 5 | 0.05ml | | 10 | 0.10ml | | 15 | 0.15ml | | 20 | 0.20ml | | 25 | 0.25ml | | 50 | 0.50ml | | 100 | 1.00ml |
Use the peptide calculators on this site to convert your desired mcg dose into units. The calculator accounts for your vial size and water volume so you do not have to do the math yourself.
Gauge Sizes
The gauge number refers to the needle's outer diameter. Higher gauge means thinner needle.
29 Gauge (29g)
The thickest commonly used for insulin/peptide injections. Draws liquid faster. Slightly more noticeable on insertion. Good general-purpose choice.
30 Gauge (30g)
A step thinner. Very common for subcutaneous peptide injections. Good balance between comfort and draw speed. Most users cannot feel the difference between 29g and 30g.
31 Gauge (31g)
The thinnest standard option. Nearly painless insertion. Takes slightly longer to draw liquid. Best for small-volume injections where draw speed does not matter.
For most peptide users, 29g or 30g works well. The comfort difference between gauges is minimal for subcutaneous injection.
Needle Lengths
Insulin syringes typically come with fixed (non-removable) needles in two lengths.
1/2 Inch (12.7mm)
Standard length. Works for both subcutaneous and shallow intramuscular injections. Suitable for most body compositions. This is the most widely available option.
5/16 Inch (8mm)
Shorter needle. Designed for subcutaneous injection only. Preferred by leaner individuals or those injecting in areas with less subcutaneous fat (like the upper arm). Also more comfortable for daily injections.
Which Syringe for Which Purpose
| Task | Recommended Syringe | |---|---| | Reconstituting (adding water) | 100-unit (1ml) | | Doses above 30 units | 50-unit or 100-unit | | Doses 10-30 units | 30-unit or 50-unit | | Doses under 10 units | 30-unit | | Semaglutide weekly dose | 50-unit or 100-unit | | BPC-157 daily dose | 30-unit or 50-unit | | CJC-1295/Ipamorelin daily dose | 30-unit or 50-unit |
Use a separate syringe for reconstitution and for dosing. The needle dulls after puncturing the rubber stopper, making the injection less smooth. Many users keep a box of 100-unit syringes for reconstitution and a box of 30-unit syringes for daily injections.