Milli, micro and the decimal point
A milligram is a thousandth of a gram and a microgram (mcg or µg) is a thousandth of a milligram, so 1 g = 1,000 mg = 1,000,000 mcg. Medication strengths are almost always in milligrams — a 500 mg tablet is half a gram — while vitamins such as B12, D and folate are often in micrograms, a thousand times smaller. Reading mcg as mg is a thousand-fold error, which is why the microgram row is shown alongside.
grams = milligrams ÷ 1,000 | milligrams = grams × 1,000
Everyday reference points
A grain of rice is about 20–30 mg; a paperclip is roughly 1 g (1,000 mg); a standard paracetamol tablet is 500 mg; the daily sodium guideline of 2,300 mg is 2.3 g, about a level teaspoon of salt. Dosage decisions belong with a pharmacist or doctor — this page only does the unit arithmetic.