Converting fresh chilli pepper to ground?
Fresh pepper/chili and ground pepper/chili are not particularly interchangeable. 

For example: (sweet) paprika is essentially ground Bell pepper, but it is not a normal substitution to use replace Bell pepper with x teaspoons of paprika. 

Additionally, peppers range in size substantially. A Thai Birdseye chili would only yield a fraction of a teaspoon when dried and ground. A bell pepper is probably more likely to yield a tablespoon or more, depending on the drying process.