How Many mg in a mL?

When converting milligrams to milliliters, the ‘m’ in both units signifies one-thousandth (1/1000) of the original unit. Therefore, to determine how many milligrams are in a milliliter, consider that a milligram is a thousandth of a thousandth of a kilogram, and a milliliter is a thousandth of a liter. Since there’s an extra thousandth in the weight unit, the conversion ratio is 1,000 milligrams in a milliliter. This gives us the formula for mg to mL conversion:


Historical Relationship: Kilogram and Liter

Originally, in 1795, the kilogram was defined as equal to one liter of water at the temperature of melting ice (0 °C / 32 °F). Although definitions have evolved, the close relationship remains.

mL to mg Conversion — mL to mg Calculator

To perform the reverse conversion (mL to mg), use the formula:


This simple calculator works both ways, providing quick conversions.

How to Use the Calculator

  1. Select Substance: Choose the substance or select “Other” and input its density.
  2. Enter Value: For mg to mL, input the milligrams; for mL to mg, input milliliters.
  3. Conversion: The calculator displays the result in the desired unit.

Example Conversion

If you have 5 grams of water (5,000 mg), using the formula ��=��1000mL=1000mg​, you get 5 mL.

Liquid Concentrations — mg in mL

For medications with liquid concentrations, often expressed in mg/mL, use the calculator to find the volume for a given amount.


Q1: How to Convert mg to mL?

  • Find substance density (e.g., water is 1000 mg/mL).
  • Divide mg by density for mL.

Q2: How to Convert mL to mg?

  • Note substance density.
  • Multiply density by mL for mg.

Q3: What is 100 mg in mL?

  • 100 mg in mL is 0.1 mL for substances with a density of 1000 mg/mL.

Q4: How much is 25 mL of cooking oil in mg?

  • For cooking oil (density 916 mg/mL), 25 mL is 22,900 mg using the formula ����ℎ�=������×�������weight=volume×density.

By understanding these relationships and using the calculator, converting between mg and mL becomes a simple and efficient process.