How we check the math

[01] The formulas

The formulas

1. Strength after mixing: mcg in the vial ÷ mL of water = mcg per mL. (1 mg = 1,000 mcg.)
2. Volume for a dose: dose in mcg ÷ strength = mL.
3. Units: on a U-100 insulin syringe, 1 mL = 100 units, so units = mL × 100.
4. Time in system: after each half-life, half of what's left remains. After 5 half-lives about 3% of one dose is left.

[02] Syringes we assume

Syringes we assume

All calculators assume U-100 insulin syringes. Most 1 mL syringes are marked every 2 units, though some brands mark every unit, and 0.3 mL and 0.5 mL syringes are marked every 1 unit. We check results against 2-unit lines on 1 mL syringes, the stricter case. If a result falls between two lines, we show the nearest line and how far off it is. U-40 and U-500 syringes are different and our calculators don't cover them.

[03] Rounding and number

Rounding and number format

We show up to two decimal places, never add trailing zeros (10 units, not 10.0), always use a leading zero (0.1 mL, not .1), write “mcg” rather than “µg” and write “units” in full. These follow medication-safety guidance on avoiding misread doses.

[04] Safety checks built

Safety checks built in

• A dose bigger than the whole vial.
• A dose that looks like mg typed as mcg, or mcg typed as mg.
• A draw bigger than the syringe holds.
• A draw between two lines, or too small to measure accurately.

[05] Testing

Testing

The math lives in one shared module that every calculator and every dose table uses, and it has automated tests with worked examples (for example, 5 mg + 2 mL with a 250 mcg dose must give 10 units). Tables on guide pages are generated by the same code, so they can't drift from the calculators. See our editorial policy for how facts are checked.