G to mg: Convert Grams to Milligrams
Convert g to mg: one gram equals 1000 milligrams. Learn the exact metric factor, where each unit is used, and common gram-to-mg values.
Why Grams to mg Comes Up
Milligrams are the unit for small doses, supplement labels, and lab measurements, while grams are the everyday metric weight. Moving between them is constant in cooking, medicine, and science.
One gram equals 1000 milligrams. Our grams converter handles grams, and the mg step is a simple power-of-ten shift you can do in your head.
The G to mg Formula
The metric system is built on powers of ten, so converting grams to milligrams means multiplying by 1000, because "milli" means one thousandth.
The Exact Calculation
For 1 g: 1 × 1000 = 1000 mg. For 5 g: 5 × 1000 = 5000 mg. The factor is exact because metric prefixes are defined powers of ten.
To go the other way, divide by 1000: 250 mg = 0.25 g. The same 1000 relationship works for any value.
Why 1000 and Not a Rounder Number
The prefix "milli" is fixed at 1/1000 in the International System of Units. That is why every gram contains exactly 1000 milligrams, and the conversion never needs a decimal factor.
What the Numbers Look Like
A typical paracetamol tablet is 500 mg, or 0.5 g. A teaspoon of salt is about 5-6 g, or 5000-6000 mg. Supplement powders list amounts like 250 mg (0.25 g) or 1000 mg (1 g).
For a related small weight, our guide to 1 oz to grams covers the ounce side of the scale.
G to mg Compared With Nearby Weights
Reference points: 0.5 g = 500 mg, 2 g = 2000 mg, 10 g = 10000 mg. Each gram adds a steady 1000 mg.
The reverse, mg to g, divides by 1000, so 100 mg is 0.1 g and 50 mg is 0.05 g.
When You Need G in mg
The conversion matters for dosing and formulation. A recipe or prescription in grams maps to milligrams on a precise scale; a nutrition label in mg maps back to grams for daily totals.
It also helps compare product strengths, since supplements and medicines quote milligrams while bulk ingredients are weighed in grams.
Frequently Asked Questions
How many mg is 1 g?
1 gram equals exactly 1000 mg, because "milli" means one thousandth in the metric system.
How do I convert g to mg?
Multiply grams by 1000. For 5 g: 5 × 1000 = 5000 mg.
How many mg is 500 g?
500 g equals 500,000 mg (500 × 1000).
Is mg smaller than g?
Yes. A milligram is one thousandth of a gram, so it takes 1000 mg to make 1 g.
How do I convert mg to g?
Divide milligrams by 1000. For 250 mg: 250 / 1000 = 0.25 g.
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Quick Summary
1 gram equals 1000 milligrams. Multiply grams by 1000 (the exact metric "milli" factor): 1 × 1000 = 1000 mg. The reverse divides by 1000.
Related Guide
1 oz to Grams: What One Ounce Equals
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Read Full Guide →Reverse conversion
mg to g: Convert Milligrams to Grams
Convert mg to g: 1000 milligrams equals 1 gram. Learn the exact metric factor, where milligrams appear, and common mg-to-g values.
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Disclaimer
Unit conversions on this site use internationally recognized, fixed conversion factors (for example, 1 inch = 2.54 cm, 1 pound = 0.45359237 kg, 1 °F = (°C × 9/5) + 32). They are provided for general, informational, and educational use. For applications where accuracy is critical — such as medical dosing, engineering, scientific research, trade, or legal compliance — always verify results against authoritative sources such as the U.S. National Institute of Standards and Technology (NIST) and the official International System of Units (SI) brochure, and follow any applicable local standards.
Exact Constants & Authoritative Sources
Every conversion on this page uses the fixed, internationally agreed constants below — drawn from NIST and the SI Brochure. No values are estimated or rounded as if exact. See the full list on our Sources & Standards page.
- EXACT1 pound (lb, avoirdupois) = 0.45359237 kilograms (exact)
- EXACT1 ounce (oz, avoirdupois) = 28.349523125 grams (exact, 1/16 lb)
- EXACT1 stone (st) = 6.35029318 kilograms (exact, 14 lb)
- EXACT1 short ton (US) = 907.18474 kilograms (exact, 2000 lb)
Common Pitfalls & How to Avoid Them
Mass vs. weight
The pound and kilogram are units of MASS, not force. On Earth, mass and "weight" read the same number in practice, but a 70 kg mass weighs less on the Moon. UnitFig converts mass; for scientific force you need newtons (1 lbf = 4.4482216152605 N, exact).
Avoirdupois vs. troy ounce
Cooking and body weight use the avoirdupois ounce (28.349523125 g). Gold and precious metals use the troy ounce (31.1034768 g). Never mix them — the error is about 10%.
Rounding the factor
Using 2.2 instead of the exact 2.20462262 overstates small errors at large values. For medical dosing or competition weight classes, keep the full factor or use a converter.
A unit-conversion reference site has no manufacturer-specific or device calibration parameters, so "layered tuning" does not apply here. The only real error-handling is input validation: the converter rejects non-numeric, empty, or out-of-range entries and shows a clear message, then falls back to exact constants above. No estimated or rounded figures are ever presented as exact.
Authoritative sources for this page
- NIST (U.S. National Institute of Standards and Technology) — NIST SP 330 — The International System of Units (SI), 2019 edition
Last Updated 2026 | This article was reviewed for accuracy