Tools
Dosage calculator
Pick a compound to load its typical vial and dose, or enter your own numbers. The result is the mark to draw to on the syringe you actually own — which is why the syringe scale matters as much as the arithmetic.
Enter your own vial, dose, and water below.
Reconstitution
Enter the vial and the water. The result is the mark to draw to on your syringe.
Draw to10units
- 0.1 mL
- Volume per dose
- 2.5 mg/mL
- Concentration
- 20
- Doses per vial
How it’s calculated
Concentration 5 mg ÷ 2 mL = 2.5 mg/mL
Volume 0.25 mg ÷ 2.5 mg/mL = 0.1 mL
Units 0.1 mL × 100 (U-100: 1 mL = 100 units) = 10
U-100 and U-40 are two different rulers
Insulin syringes are marked in units, not millilitres, and the unit is defined by the insulin concentration the syringe was built for. A 1 mL barrel holds 1 mL either way. What changes is how that millilitre is divided.
U-100
1 mL = 100 units · 1 unit = 0.01 mL
The standard human insulin syringe and what almost every online dosing figure assumes. A 50-unit mark is half a millilitre.
U-40
1 mL = 40 units · 1 unit = 0.025 mL
Built for U-40 insulin, still common in veterinary supply. The same volume reads as a much smaller number of units, so a dose drawn to the U-100 figure delivers 2.5× too much.
Reading a U-40 mark on a U-100 syringe, or the reverse, misdoses by a factor of 2.5. Check the barrel print before every draw and set the toggle to match the syringe in your hand, not the one in the calculator’s memory.
Gauge, length, and what it feels like
Gauge measures the outer diameter of the needle and runs backwards: the higher the number, the thinner the needle. Thinner needles hurt less and bruise less; thicker ones draw viscous liquid faster and bend less. Most subcutaneous injection is done with a short, fine needle, and drawing from the vial is often done with a thicker one that is then swapped.
- 18G1.27 mm
Drawing bacteriostatic water or reconstituting, never for injecting.
Would be sharply painful in skin. Used only to move liquid quickly and to avoid coring the stopper.
- 21–23G0.82–0.64 mm
Drawing from the vial; intramuscular injection where volume is larger.
Clearly felt going in, with soreness afterwards. Most people swap to a finer needle before injecting.
- 27G0.41 mm
Subcutaneous injection where the liquid is thicker or the dose larger.
A distinct pinch on entry. Tolerable, but noticeable on every injection.
- 29–30G0.34–0.31 mm
The usual range for insulin syringes and routine subcutaneous dosing.
A brief scratch. Many injections are felt only as pressure, particularly in abdominal fat.
- 31–32G0.26–0.23 mm
Small subcutaneous volumes with thin, fully dissolved solution.
Often not felt at all. Fine enough to bend if the angle is wrong, and slow to push viscous liquid.
Length matters as much as gauge. Subcutaneous injection needs 4–8 mm; longer needles reach muscle, which changes absorption and stings more. Sensation also depends on site, injection speed, whether the liquid is cold, and how many times the needle has been used — a needle is blunted by its first pass through a vial stopper.
Getting the dose right
- Set the syringe toggle to match the barrel in your hand before reading the result.
- Choose the water volume so the dose lands on a whole mark rather than between two — round the water, not the dose.
- Keep the same concentration across a vial. Re-diluting mid-vial invalidates every figure you wrote down.
- Write the concentration and the mix date on the vial in permanent marker.
- Draw slowly and hold the syringe vertical to clear bubbles; air in the barrel means the mark is not the dose.
Where the arithmetic goes wrong
- Confusing mg and mcg. One milligram is one thousand micrograms, and most dosing figures are in mcg.
- Assuming units are volume. A unit is a mark on a scale, and the scale depends on the syringe.
- Reusing a figure from a different vial size. Concentration changes with both powder and water.
- Trusting the vial label. The number printed on it is a claim, not a measurement.
- Reading the plunger's leading edge on one draw and its rubber tip on the next.
This calculator does arithmetic on numbers you supply. It does not know whether the dose is appropriate, whether the vial contains what the label claims, or whether the compound should be used at all.