$3 \mathrm{~g}=$ how many $\mathrm{mg}$ ?
\(\boxed{3 \text{ grams} = 3000 \text{ milligrams}}\)
Step 1 :Convert grams to milligrams: 1 gram (g) = 1000 milligrams (mg)
Step 2 :Multiply 3 grams by 1000 to convert to milligrams
Step 3 :3 g = 3 * 1000 mg = 3000 mg
Step 4 :\(\boxed{3 \text{ grams} = 3000 \text{ milligrams}}\)