I have digital scales and I measured KCl in teaspoons some time ago. All teaspoons are very different. I have 2 kinds of teaspoons - small and little bit bigger. Also you can weight it as "level" (powder is flat at the same level as teaspoon borders) and "rounded" (taking as much powder as you can, making a "hill" in a teaspoon).
So the weights are:
Small teaspoon (level): 4.3g
Bigger teaspoon (level): 5.7g
Small teaspoon (rounded): 7.9g
Bigger teaspoon (rounded): 11.0g