Teaspoons vs Milliliters vs Milligrams

Teaspoons, milliliters, and milligrams often appear together in recipes, product labels, and measurement questions, but they are not interchangeable.

Teaspoons measure volume

A teaspoon describes how much three-dimensional space a material occupies. The US teaspoon is 4.92892159375 mL; the metric teaspoon is 5 mL.

Milliliters also measure volume

Because teaspoons and milliliters both measure volume, their relationship comes directly from the teaspoon definition. No material needs to be specified to convert a US teaspoon into milliliters.

Milligrams measure mass

A milligram describes mass. There are 1,000 milligrams in one gram. The same teaspoon volume can hold different milligram masses when materials have different densities.

Density connects volume and mass

Density in grams per milliliter tells us how many grams are present in each milliliter:

mass = volume x density

After calculating grams, multiply by 1,000 to express the mass in milligrams.

A water example

At an approximate density of 1.000 g/mL, 5 mL of water has a mass of 5 g, or 5,000 mg. That is a water-specific example for a metric teaspoon, not a universal teaspoon conversion.

Use the custom density calculator when your material is not water.

Primary references

• NIST Special Publication 811, Appendix B.9 — provides the US teaspoon-to-milliliter conversion factor in its volume table.
• BIPM SI Brochure — documents the SI system and the units and prefixes behind milliliters, grams, and milligrams.