You can do that, yes. A measuring teaspoon is 5mls. Use a proper measuring spoon as normal teaspoons can differ greatly in volume.
Half a teaspoon will be 2.5mls.
I always make sure I get all the liquid in my measurer by pouring water or milk over the measurer into a cup. This stops any of the dose from sticking to the spoon and me missing out on up to half a mil.