A teaspoon is 5 ml, therefore 1/10 of a teaspoon is 0.5ml

0.5mL. Our local Target Pharmacy has little syringes measured in mL that are perfect for measuring tiny amounts.

Classically, as a cooking measure, a teaspoon is 5ml (or 5cc if you're old like me!), so 1/10 teaspoon is 0.5ml.

I justed used 1/2 of a teaspoon