Hello Viktor. For standard culinary portioning and meal prep, the standard conversions are straightforward:
One standard teaspoon is equal to 5 milliliters (mL).
One standard tablespoon is equal to 15 milliliters (mL), which is equal to 3 teaspoons.
To be completely precise with the underlying standards: in modern metric cooking and nutrition labeling across most of the world (including the US standard measuring spoons), these values are standardized to exactly 5 mL and 15 mL. If you are converting from strict US customary fluid measurements, 1 US teaspoon is technically 4.93 mL and 1 US tablespoon is 14.79 mL, but culinary tools and standard recipes always round these to 5 mL and 15 mL for practical use.
As a quick note, if you ever follow Australian recipes, be aware that an Australian tablespoon is standardized to 20 mL (4 teaspoons) rather than 15 mL. Otherwise, using 5 mL for a teaspoon and 15 mL for a tablespoon is the standard practice. I hope this helps with your meal prep!