Grams to mg converter, for the small amounts.

To convert grams to milligrams, multiply by 1,000. One gram is 1,000 mg, 0.5 g is 500 mg and 2.5 g is 2,500 mg. The sum is exact. This page does maths only. It does not know what is safe to take, so for medicine or supplements follow the label and ask a pharmacist.

How to use the converter

1. Type the amount in the Grams (g) box. A decimal such as 2.5 or a fraction such as 3/4 works.
2. The big result shows Milligrams (mg). Use Decimals in the side column to fix the number of places.
3. The cards show the same weight in micrograms and kilograms.
4. Type milligrams in the second box, or press ⇄, to go from mg to g.
5. Click a row in Common values to load it. Copy result, Copy link, Copy table and Print chart keep the answer. Start again resets the box.

Why 1,000

The prefix milli means one thousandth. NIST Handbook 44 (2026), Appendix C shows "10 milligrams = 1 centigram", "10 centigrams = 1 decigram" and "10 decigrams = 1 gram = 1,000 milligrams". Checked 24 Oct 2026. Multiply by ten three times and you reach 1,000. The ladder is worth knowing in both directions: 1 mg is 0.001 g, and 1 g is 1,000,000 micrograms (µg or mcg), which is 1,000 times smaller again.

The mg and µg trap

The slip that matters most is mixing up milligrams (mg) and micrograms (µg, often written mcg). 1 mg is 1,000 µg. A value of 0.025 g is 25 mg, which is 25,000 µg. If a label gives µg and your scale reads mg, convert before comparing, and never assume the two are the same size. The tool shows the microgram card for exactly this reason.

Worked examples

• A 0.5 g tablet. 0.5 × 1,000 = 500 mg.
• A 0.06 g pinch of spice. 60 mg.
• 1.5 g of salt. 1,500 mg. Amounts like this are often quoted in mg in one place and weighed in g in another, so it is a common sum.
• A jewellery scale reading of 0.003 g. 3 mg.
• The other way. 750 mg ÷ 1,000 = 0.75 g. Type 750 in the milligrams box.
• Six 250 mg doses on a label. 6 × 250 = 1,500 mg, which is 1.5 g in total.

From a per-100 g amount to a portion

Amounts are often listed per 100 g. To find what a portion holds, scale the amount by the portion's weight. If something holds 40 mg per 100 g, a 250 g portion holds 40 × 2.5 = 100 mg. If the figure is given in grams, such as 0.04 g per 100 g, convert it first: 40 mg. Doing the unit change before the scaling keeps the digits in the right place.

A handy ratio

Milligrams per gram and grams per kilogram are the same number, because both are one part in a thousand. A product with 5 g in each kilogram holds 5,000 mg in each gram. The tool does not need that shortcut, but it is a good way to check an answer.

How many decimals to keep

The finest step on a scale sets how many digits mean anything. A scale that reads to 0.01 g steps in 10 mg, so 0.37 g is 370 mg, and a reading of 0.375 g cannot exist on it. A scale that reads to 0.001 g steps in 1 mg. Keep as many digits as the scale has, and no more: converting 0.37 g to 370 mg adds no precision, it only changes the unit.

Small numbers on a scale

Many kitchen scales only show whole grams, so a reading of 0 or 1 g hides a lot of milligrams. A scale that reads to 0.01 g, which is 10 mg, can be needed for spices, yeast or supplements in a recipe. When your answer is under 1 mg, use the Decimals setting so you see enough digits. Auto adds places for small numbers, so 0.4 mg for 0.0004 g shows in full.

Related pages: Mg to grams, Grams to kg, Kg to grams, and mL to grams for liquids.