Convert Mass from Gram to Microgram (g to mcg)

Gram to Microgram Conversion Formula

To convert from Gram (g) to Microgram (mcg), use the following formula:

Example

Let's convert 5 Gram (g) to Microgram (mcg).

Using the formula:

Therefore, 5 Gram (g) is equal to $5000000$ Microgram (mcg).

What is a Gram (g)?

A gram (g) is a base unit of mass in the metric system. The plural form is grams.

Where Did the Gram Originally Come From?

The gram was initially defined in 1795 by the French National Convention.

Its first definition was based on the mass of one cubic centimeter of pure water at the temperature of its maximum density, which is approximately 4 degrees Celsius (4 °C).

This practical, water-based definition was a revolutionary step toward a standardized and universal system of measurement, moving away from the inconsistent and often confusing units of time.

Grams vs. Ounces: What's the Difference?

A gram is much smaller than an ounce, the standard unit of mass in the imperial and US customary systems.

One ounce equals approximately 28.35 grams, which is why grams are preferred for scientific work and for measuring small amounts, such as spices or medicine.

The metric system's decimal structure (for example, 1,000 grams in a kilogram) also makes calculations simpler than in the imperial system.

How Is the Gram Defined Today?

Although the gram was once tied to water, it's no longer linked to any physical object.

Since 2019, the kilogram — and therefore the gram — is defined by a fundamental constant, the Planck constant (h).

That shift makes the unit stable and reproducible in any properly equipped laboratory, without relying on the old International Prototype of the Kilogram.

What is a Microgram (mcg)?

A microgram (mcg) is a unit of mass equal to one-millionth of a gram.

Why Are There Two Symbols for a Microgram (mcg vs. μg)?

While the official symbol for the microgram in the International System of Units (SI) is μg (using the Greek letter Mu), you'll often see it written as mcg.

This is particularly common in the medical and pharmaceutical fields.

Using 'mcg' is a crucial safety measure to prevent dosage errors. A handwritten 'μg' could easily be mistaken for 'mg' (milligram), which would result in a 1,000-times overdose—a potentially fatal mistake.

Why Are Micrograms Important in Medicine?

The microgram is the go-to unit for measuring very potent substances, where tiny differences matter for both safety and effectiveness.

It's used for specific substances like:

• Vitamins (such as vitamin D, B12, and folic acid)
• Trace minerals (like iodine and selenium)
• Powerful medications (including certain thyroid hormones and chemotherapy drugs)

Measuring in micrograms makes it possible to give an effective dose without risking toxicity.

How Small Is a Microgram? A Visual Comparison

It's hard to picture how tiny a microgram is.

For perspective, a single grain of ordinary table salt weighs about 500–600 micrograms — meaning a single grain contains more than 500 micrograms.

That helps explain why we measure very potent substances in micrograms: their active doses are tiny.

What is the metric system?

Gram to Microgram Conversion Table

Here are some quick reference conversions from Gram (g) to Microgram (mcg):