Weight Conversion Reference
Body weight is the most frequently converted clinical measurement, it underlies drug dosing calculations, IV fluid rates, and weight-based risk assessments such as BMI. Because the US, UK, and metric-only countries all use different default units, unit errors during conversion are a recognised source of documentation mistakes, always double-check which unit a chart or prescription is actually using before entering a value.
| Unit | Equivalent in kg | Clinical Use |
|---|---|---|
| 1 kg | 1.000 kg | Standard metric body weight, drug dosing |
| 1 pound (lb) | 0.4536 kg | Body weight in US, UK (alongside stone) |
| 1 stone (st) | 6.3503 kg | Body weight in UK/Ireland |
| 1 ounce (oz) | 0.02835 kg | Small ingredient weights, neonatal weight |
| 1 gram (g) | 0.001 kg | Drug mass, IV infusion amounts |
| 1 milligram (mg) | 0.000001 kg | Standard oral drug dose unit |
| 1 microgram (mcg) | 10⁻⁹ kg | Potent drugs: digoxin, fentanyl, levothyroxine |
Why the Unit You See Depends on Where You Are
The same weight can appear in kilograms, pounds, or stone depending on the country and even the specific form. The NHS's own health assessment tools accept weight in stone and pounds directly, reflecting how UK adults actually think about their weight day to day, even though the underlying clinical record is usually kept in kilograms.
Dosing Drugs Measured in Micrograms
Drugs dosed in micrograms are typically the most potent, and often calculated per kilogram of body weight rather than as a flat dose. For weight-based dosing calculations, see our Weight-Based Dose Calculator.
Stone + Pounds Display
In the UK and Ireland, body weight is often expressed as a combination, e.g. "11 stone 4 pounds" (11 st 4 lbs). To convert: total pounds = (stone × 14) + remaining pounds, then multiply by 0.4536 to get kg. Our stone display shows the decimal stone value; for st + lbs format use: integer part = stone, remainder × 14 = pounds.