Graduations and readability
Arithmetic has unlimited precision. A barrel marked every unit does not. The gap between them is worth knowing in numbers.
Educational arithmetic only. Not medical advice and not a dosing protocol.
| Volume drawn | Units on U-100 | Error from a half-unit misread |
|---|---|---|
| 0.01 mL | 1.0 | ±50.0% |
| 0.02 mL | 2.0 | ±25.0% |
| 0.03 mL | 3.0 | ±16.7% |
| 0.05 mL | 5.0 | ±10.0% |
| 0.1 mL | 10.0 | ±5.0% |
| 0.15 mL | 15.0 | ±3.3% |
| 0.2 mL | 20.0 | ±2.5% |
| 0.3 mL | 30.0 | ±1.7% |
| 0.5 mL | 50.0 | ±1.0% |
Read this with the answer
This is educational arithmetic on figures entered by the reader. It is not medical advice, not a dosing protocol, and not a recommendation that anything be prepared, obtained or administered.
Nothing here states what quantity is appropriate for anyone, and there is no function in it that produces an amount to administer. A question about anyone’s health belongs with a licensed clinician who can examine the person asking.
Most compounds named here are research chemicals that are not approved by the FDA for human use. An exact calculation is not an accurate measurement: what is actually in a syringe depends on the preparation and the device, neither of which this page can see.
The percentages above are arithmetic on the printed calibration. Real measurement error also includes the device’s own tolerance, dead space, air, technique and eyesight, none of which this page can quantify and all of which make the true figure larger.
No qualified clinical reviewer is recorded against this site, and no credential is claimed anywhere on it. Full disclaimer.
Reading the table
At 0.2 mL, twenty units on a U-100 barrel, misreading by half a unit costs 2.5% of the amount drawn. At 0.02 mL, two units, the same half-unit misread costs 25%. The arithmetic is identical in both cases and equally exact; what changes is how much of the answer survives contact with the barrel.
That is why this site reports the nearest printed mark alongside the exact figure, and warns when a draw sits within two graduations of zero. A tool that prints 1.37 units to two decimal places on a barrel marked in whole units has implied a precision the device cannot deliver.
Dilution moves the number in the right direction
The same amount in a weaker solution is a longer draw, and a longer draw spends a smaller share of itself on the reading error. Halving the concentration doubles the volume and halves the percentage in the right-hand column.
The cost is a larger total volume, a second preparation step, and one more figure that has to be right. The dilution calculator does that arithmetic, and the diluent-for-a-target calculator works backwards from a concentration chosen for readability.
Rounding here is half away from zero, and stated
When this site names a nearest printed mark, the rounding is half away from zero: 7.5 units rounds to 8, and 7.5 rounds to 8 rather than to the nearest even number. That convention is stated rather than left to be inferred, because two rounding conventions disagree exactly at the midpoint, which is where someone squinting at a barrel is most likely to be.