Methodology and sources
Every number on this site comes from one small piece of code with a test for each formula. Here's what it uses and why.
Syringe units
mL = dose (mg) ÷ concentration (mg/mL) units = mL × 100 (U-100 syringe; × 40 for U-40)
A U-100 syringe is calibrated so 100 units fill 1 mL. Barrel sizes and markings: 0.3 mL (30 units, 1-unit lines; half-unit lines on some brands), 0.5 mL (50 units, 1-unit lines), 1 mL (100 units, 2-unit lines). Source: BD syringe specifications.
International Unit factors
| Substance | 1 IU = | 1,000 IU = | Source |
|---|---|---|---|
| Vitamin D (D3 or D2) | 0.025 mcg | 25 mcg | NIH ODS |
| Vitamin E, natural (d-alpha) | 0.67 mg | 670 mg | NIH ODS |
| Vitamin E, synthetic (dl-alpha) | 0.45 mg | 450 mg | NIH ODS |
| Vitamin A as retinol | 0.3 mcg RAE | 300 mcg RAE | NIH ODS |
| Beta-carotene, supplements | 0.3 mcg RAE | 300 mcg RAE | NIH ODS |
| Beta-carotene, food | 0.05 mcg RAE | 50 mcg RAE | NIH ODS |
| Insulin, human | 0.0347 mg | 34.7 mg | WHO standard |
| Heparin | no fixed factor | — | USP |
- Vitamin D: 1 mcg = 40 IU (NIH Office of Dietary Supplements).
- Vitamin E: 1 IU = 0.67 mg alpha-tocopherol (natural, d-alpha) or 0.45 mg (synthetic, dl-alpha) (NIH ODS).
- Vitamin A: 1 IU retinol = 0.3 mcg RAE; 1 IU beta-carotene from supplements = 0.3 mcg RAE; from food = 0.05 mcg RAE (NIH ODS).
- Insulin (human): 1 IU = 0.0347 mg (WHO International Standard). Insulin analogues have their own factors, so don't use this for them.
- Heparin: no fixed factor. Potency is assayed per batch (USP units), so it isn't converted.
Dosing schedules
Where a page shows a titration schedule (tirzepatide, semaglutide), it is taken from the FDA prescribing information for the brand-name product and cited on that page. We show it so you can find your dose in a table, not as advice to follow it.
Rounding
Calculations keep full precision. Results are shown rounded half up: syringe units to 1 decimal, mL to 3 decimals, mg to 3 or 4 decimals. When a dose falls between syringe lines, the calculator says so and shows the nearest line instead of rounding silently.
Tests
Before every release, automated tests check each formula against hand-worked reference values (for example 5 mg at 10 mg/mL = 50 units, 1,000 IU vitamin D = 25 mcg, 400 IU natural vitamin E = 268 mg), check edge cases (zero, negative and non-numeric input), and recompute every value in every table on the site. A single failure stops the release.