mg to mL Calculator (mass ↔ volume at a known concentration)

Understanding the mg to mL calculator — concept and principle

This calculator converts between the mass of a dissolved substance in milligrams and the volume of solution in millilitres, using the solution's concentration. It works both ways: the volume that holds a given mass, or the mass in a given volume. Lab students, technicians and anyone preparing or diluting a solution from a stock use it.

Dose ÷ concentration = volume — with the default inputs: 7.5 mL.

How it is calculated

Mass concentration ρ = mass of solute ÷ volume of solution
Volume (mL) = mass (mg) ÷ concentration (mg/mL)
Mass (mg) = concentration (mg/mL) × volume (mL)
Concentrations are first converted to mg/mL: 1 g/L = 1 mg/mL; 1 µg/mL = 0.001 mg/mL; 1 mg/L = 0.001 mg/mL
Masses: 1 g = 1,000 mg; 1 µg = 0.001 mg

The principle

Milligrams measure mass and millilitres measure volume, so they cannot be converted directly. The link is the mass concentration, which IUPAC defines as the mass of a constituent divided by the volume of the mixture. Once you know how many milligrams are in each millilitre, any mass corresponds to a definite volume. Only for pure water near room temperature does 1 mL weigh about 1 g; for a solution, that is the density, a different quantity from its concentration.

Worked example

Defaults: 150 mg of solute; stock concentration 20 mg/mL; mg → mL.

Concentration = 20 mg/mL.
Volume = 150 ÷ 20 = 7.5 mL.
In microlitres = 7.5 × 1,000 = 7,500 µL.
Mass = 150 mg = 0.15 g.

Each point is the calculator re-run with only “Concentration of the solution” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Concentration of the solution	Result
5	30 mL
10	15 mL
15	10 mL
20	7.5 mL
25	6 mL
30	5 mL
40	3.75 mL

How to read the result

Measure the volume with a tool suited to its size: a pipette or syringe for a few millilitres, a micropipette for microlitres. If the volume is tiny, consider diluting the stock first to measure more accurately. Always check that the concentration and the label refer to the same substance form, for example a salt versus the active ion.

Common mistakes

Treating mg and mL as equal for any liquid.
Mixing mg/L with mg/mL, a factor of 1,000.
Using the concentration of the solid instead of the solution.
Rounding a small volume too early.

Keep in mind: For medicines, follow the prescription and product label, and ask a pharmacist or doctor. This tool performs arithmetic only and is not medical advice.

Frequently asked questions

How many mL is 100 mg?

It depends on the concentration. At 20 mg/mL it is 5 mL; without a concentration there is no answer.

Is 1 mg/mL the same as 1 g/L?

Yes. Both equal 1,000 mg in 1,000 mL.

Does 1 mL of water weigh 1 g?

Approximately, at room temperature. That is water's density, not a general conversion.

Sources: IUPAC Compendium of Chemical Terminology (Gold Book), "mass concentration" · BIPM, SI Brochure, 9th ed. (2019), SI prefixes

Checked 9 Nov 2026. IUPAC Compendium of Chemical Terminology (Gold Book), “mass concentration” (doi:10.1351/goldbook.M03713): mass of a constituent divided by the volume of the mixture; SI prefixes from the SI Brochure (BIPM, 9th ed., 2019).

Your numbers