It is recommended that men over the age of 18 consume 90mg of Vitamin C per day while for women over the age of 18 should consume 75mg per day. While slightly larger amounts of Vitamin C may not be harmful, usually consuming more than the needed Vitamin C will simply pass through the body without adequate processing. If very large amounts are consumed (over 2000mg) then it can actually harm the body.
This is a very common question. However, knowing how much is in a teaspoon is not very useful for measuring a daily dosage since a teaspoon contains over a month worth of nutritional value. A teaspoon amount is only useful for cooking recipes or when dividing the ascorbic acid into the volume of something bigger to be consumed over time (a container of water that can be measured again into smaller quantities). For direct daily intake, a pocket scale should be utilized for measuring out the milligrams (1000mg = 1g). In case you need to know how much is in a teaspoon, see the "density" paragraph below.
The density of the 80 mesh ascorbic acid powder varies between 0.9-1.2 g/ml. There is about 5 ml in 1 US teaspoon. So there is a range of 4.5g-6g, or 4500-6000mg of ascorbic acid per teaspoon. If you are an adult male that needs 75mg of ascorbic acid, a teaspoon results in at least 6000% of your daily needed intake. To take the proper amount, you would need to consume no more than 1.67% of a teaspoon. This is impossible to measure and so we recommend to either mix this teaspoon into something else and divide that food up appropriately or to use a pocket scale with 0.01g reading accuracy to measure it out.