To convert milliliters to teaspoons (mL to tsp), multiply by 0.202884136. 1 milliliter equals 0.202884136 tsp, about 20% of a teaspoon.
| milliliters | teaspoons |
|---|---|
| 1 milliliter | 0.20288 tsp |
| 2 milliliters | 0.40577 tsp |
| 5 milliliters | 1.0144207 tsp |
| 10 milliliters | 2.0288414 tsp |
| 25 milliliters | 5.0721034 tsp |
| 50 milliliters | 10.144207 tsp |
| 100 milliliters | 20.288414 tsp |
| 250 milliliters | 50.721034 tsp |
| 500 milliliters | 101.44207 tsp |
| 1000 milliliters | 202.88414 tsp |
The relationship is exact, 1 ÷ 4.92892159375, but no decimal can express it exactly. 0.202884136 is rounded, and so is every other decimal you will see for it.
For a quick estimate, multiply by 0.2. That is off by about 1.4%, which is fine for a rough figure and not fine for anything you are paying for or building to. When it matters, use the exact relationship: 1 ÷ 4.92892159375. Its decimal never terminates, so 0.202884136 is already rounded.
Going the other way, one teaspoon is 4.929 mL, which is usually the easier direction to work in. Because the forward factor is small, watch the decimal place rather than the digits: a factor-of-ten slip is the common error, not a rounding one.
To anchor the scale: 5 milliliters is about 1.01 tsp.