What's the difference between a 100u, 50u, and 30u insulin syringe?

All three are insulin syringes with the same gauge (typically 29G or 31G). They differ in maximum capacity: 100u = 1 mL, 50u = 0.5 mL, 30u = 0.3 mL. The 50u and 30u have finer tick marks per unit (better for very small doses, like 2.5 units of BPC), while the 100u holds more (necessary for higher doses like 50+ units of Tirzepatide). The math for converting volume to units is the same on all of them.

Why do peptide calculators say 'units' instead of 'mL'?

Insulin syringes are graduated in 'insulin units' (a legacy of dosing insulin, which is measured in IU). 1 mL = 100 units on a standard 100u syringe. Units are easier to read in the marked increments — you draw to the 25 line, not to 0.25 mL. Internally though, units and mL × 100 are identical.

Learn · How to

How to calculate peptide dosage.

Q: How many units of BPC-157 is 250 mcg?

It depends on how you reconstituted the vial. For a 10 mg vial in 1 mL of bacteriostatic water (the Goodtides standard recon), 250 mcg = 2.5 units on a 100-unit insulin syringe. For a 5 mg vial in 1 mL of water, 250 mcg = 5 units. The math: units = (target dose mg ÷ (vial mg ÷ water mL)) × 100.

Q: How many units of Tirzepatide is 2.5 mg?

For a 10 mg Tirzepatide vial in 1 mL of bacteriostatic water (10 mg/mL concentration), 2.5 mg = 0.25 mL = 25 units. As you titrate up: 5 mg = 50 units, 7.5 mg = 75 units, 10 mg = 100 units (the full syringe).

Q: How do you dose a peptide blend like KLOW?

Blends are dosed by volume (insulin units), not by individual peptide amount. A KLOW vial (80 mg total: BPC-157 10 mg + TB-500 10 mg + KPV 10 mg + GHK-Cu 50 mg) reconstituted in 3 mL of bacteriostatic water yields 26.7 mg/mL. Most users start at 15 units (= 0.15 mL = 4 mg blend = 0.5 mg BPC + 0.5 mg TB + 0.5 mg KPV + 2.5 mg GHK-Cu) and titrate to 30 units daily.

Q: What if my calculated dose is more than my syringe holds?

Two options: (1) reconstitute the vial with more bacteriostatic water (more dilute → smaller volume per dose), or (2) split into two injections at different sites. Example: 5 mg of Tirzepatide on a 50u syringe (0.5 mL max) requires 10 mg/mL concentration or higher. If your vial is 5 mg in 1 mL (5 mg/mL), 5 mg = 1 mL = doesn't fit. Re-recon with 0.5 mL of BAC water → 10 mg/mL → 5 mg = 0.5 mL = full 50u syringe. Or split the dose across two morning + night injections.

Three inputs — vial size, water you reconstituted with, and your target dose — get you the exact insulin-syringe units to draw. The math is simple once you see it once.

The formula

Every peptide dose calculation comes down to this:

concentration (mg/mL) = vial_mg ÷ water_mL
volume (mL) = target_dose_mg ÷ concentration
units = volume × 100
For a 100-unit (1 mL) insulin syringe. Units are 1:1 with mL × 100 across all insulin syringe sizes.

The 5 steps

Read your vial label for the mg amount. Standard Goodtides vials are 10 mg.
Check how much bacteriostatic water you used to reconstitute. Most peptides at Goodtides recon at 1 mL per 10 mg (1:1 ratio).
Convert your target dose to mg. Doses in mcg divide by 1000 (e.g. 250 mcg = 0.25 mg).
Compute concentration: vial mg ÷ water mL. For 10 mg / 1 mL = 10 mg/mL.
Compute units: (target dose mg ÷ concentration) × 100.

Worked examples

BPC-157 at 250 mcg

10 mg vial · 1 mL BAC water · 250 mcg target

concentration = 10 ÷ 1 = 10 mg/mL

volume = 0.25 ÷ 10 = 0.025 mL

units = 0.025 × 100 = 2.5 units

Draw to the 2.5 line on a 100u insulin syringe — or use a 50u syringe for finer resolution.

Tirzepatide titration ladder

10 mg vial · 1 mL BAC water · weekly

concentration = 10 mg/mL throughout the cycle

Starting 2.5 mg → 25 units · Week 5 (5 mg) → 50 units · Week 9 (7.5 mg) → 75 units · Week 13 (10 mg) → 100 units (the whole syringe).

For doses above 100 units you can either split into two injections or re-reconstitute with less water (e.g. 0.5 mL) to double the concentration.

KLOW blend (volume-anchored)

80 mg total (BPC 10 + TB 10 + KPV 10 + GHK-Cu 50) · 3 mL BAC water · daily

Blends are dosed by volume, not by individual component.

concentration = 80 ÷ 3 = 26.67 mg/mL of total blend

Most users start at 15 units (0.15 mL = 4 mg blend) daily and titrate up to 30 units (0.30 mL = 8 mg blend). At 30 units that's 1 mg of BPC + 1 mg of TB + 1 mg of KPV + 5 mg of GHK-Cu per injection.

Use the calculator instead

Don't memorize the math — let it do the work. We built two free tools that handle this automatically:

Free · No signup

Web dose calculator

Pick a peptide, enter your vial and water, get units. Includes blend breakdowns.

Free PWA · Installable

Goodtides Companion

Calculator + injection log + vial tracking + protocol scheduling. Add to home screen.

Common mistakes

Mixing up mcg and mg. 1 mg = 1000 mcg. A "250" target is most often 250 mcg (= 0.25 mg) — not 250 mg.
Forgetting concentration changes with recon volume. If you decide to use 2 mL of water instead of 1 mL, your concentration halves — and so do your units per dose.
Reading 100u syringe tick marks as mL. They're units. 25 on the syringe = 0.25 mL, not 25 mL.
Drawing too small a dose on a 100u syringe. Doses below ~3 units on a 100u syringe are hard to measure precisely. Use a 50u or 30u syringe, or re-reconstitute with more water.

Frequently asked

How many units of BPC-157 is 250 mcg?

For a 10 mg vial in 1 mL of BAC water (Goodtides standard), 250 mcg = 2.5 units on a 100-unit insulin syringe. The math: (0.25 mg ÷ 10 mg/mL) × 100 = 2.5 units.

How many units of Tirzepatide is 2.5 mg?

For a 10 mg Tirzepatide vial in 1 mL of BAC water (10 mg/mL), 2.5 mg = 25 units. Titrating up: 5 mg = 50 units, 7.5 mg = 75 units, 10 mg = 100 units (the full syringe).

How do you dose a peptide blend like KLOW?

Blends are dosed by volume (insulin units), not by component. A KLOW vial (80 mg blend: BPC 10 + TB 10 + KPV 10 + GHK-Cu 50) in 3 mL of water yields 26.7 mg/mL. Most users start at 15 units daily and titrate to 30 units. At 30 units each injection delivers 1 mg BPC + 1 mg TB + 1 mg KPV + 5 mg GHK-Cu.

What's the difference between 100u, 50u, and 30u insulin syringes?

All same gauge, different capacity: 100u = 1 mL, 50u = 0.5 mL, 30u = 0.3 mL. The 50u and 30u have finer per-unit resolution (better for small doses like 2.5u of BPC); the 100u holds more (necessary for 50+ unit doses like Tirzepatide).

Can I use a regular syringe instead of insulin?

Technically yes, but insulin syringes are strongly preferred: finer gauges (less painful), shorter needles (correct depth for subQ), graduated in units (easier to measure tiny volumes), and fixed needles (less dead-space waste). The Tide Kit ships with 29G insulin syringes by default.

What if my calculated dose is more than my syringe holds?

Two options: (1) re-reconstitute the vial with less BAC water (higher concentration = smaller volume per dose), or (2) split the dose across two injection sites. For example, 5 mg of Tirzepatide on a 50u syringe doesn't fit at 5 mg/mL — but recon with 0.5 mL water → 10 mg/mL → 5 mg = 50 units exactly.

For research peptide users tracking their own protocol. Not medical advice. Peptides referenced here are research chemicals, not FDA-approved drugs. Consult a qualified clinician for medical decisions.